WATER , SANITATION AND HEALTH – A REVIEW

 

Compiled from various sources by James J. Sharp

 

INTRODUCTION

Every day, about 10,000 people die unnecessarily from diarrhoeal diseases. Many, if not most of these are children. Their deaths are caused because they and their families, along with 70% of the people in the developing world, have no access to even the most basic sanitation services. Many gatherings of World leaders have agreed that a safe supply of drinking water and hygienic means of sanitation are basic human needs. How has this situation arisen, what causes it to happen and how are things changing ? For an answer we need to look at how water supplies developed and how people disposed of their wastes. Many of the problems experienced today were not significant in times when the world’s population was much smaller. In these days there was less pollution because there were fewer people and virtually no industry.

Water was an important factor in the location of the earliest settled communities, and the evolution of public water supply systems is tied directly to the growth of cities. In the development of water resources beyond their natural condition in rivers, lakes, and springs, the digging of shallow wells was probably the earliest innovation. As the need for water increased and tools were developed, wells were made deeper. Brick-lined wells were built by city dwellers in the Indus River Basin as early as 2500 BC, and wells more than 1,600 feet (almost 500 metres) deep are known to have been used in ancient China.

Construction of qanats, slightly sloping tunnels driven into hillsides that contained groundwater, probably originated in north-western Persia (now Armenia) about 700 BC. From the hillsides the water was conveyed by gravity in open channels to nearby towns or cities. The use of qanats became widespread throughout the region, and some are still in existence. Until 1933 the Iranian capital city, Tehran, drew its entire water supply from a system of qanats.

The need to channel water supplies from distant sources was an outcome of the growth of urban communities. Among the most notable of ancient water conveyance systems are the aqueducts built between 312 BC and AD 455 throughout the Roman Empire. Some of these impressive works are still in existence. The writings of Sextus Julius Frontinus (who was appointed superintendent of Roman aqueducts in AD 97) provide information about the design and construction of the 11 major aqueducts that supplied Rome itself. Extending from a distant spring-fed area, a lake, or a river, a typical Roman aqueduct included a series of underground and aboveground channels. The longest was the Aqua Marcia, built in 144 BC. Its source was about 37 km from Rome. The aqueduct itself was 92 km long, however, because it had to meander along land contours in order to maintain a steady flow of water. For about 80 km the aqueduct was underground in a covered trench, and only for the last 11 km was it carried above ground. In fact, most of the combined length of the aqueducts supplying Rome (420 km) was built as covered trenches or tunnels. When crossing a valley, aqueducts were supported by structures comprising one or more levels of massive granite piers and impressive arches.

The aqueducts ended in Rome at distribution reservoirs, from which the water was conveyed to public baths or fountains. A few very wealthy or privileged citizens had water piped directly into their homes, but most of the people carried water in containers from a public fountain. Water was running constantly, the excess being used to clean the streets and flush the sewers. Ancient aqueducts and pipelines were not capable of withstanding much pressure. Channels were constructed of cut stone, brick, rubble, or rough concrete. Pipes were typically made of drilled stone or of hollowed wooden logs, although clay and lead pipes were also used.

During the Middle Ages there was no notable progress in the methods or materials used to convey and distribute water. Cast-iron pipes with joints capable of withstanding high pressures were not used very much until the early l9th century. The steam engine was first applied to water pumping operations at about that time, making it possible for all but the smallest communities to have drinking water supplied directly to individual homes. Asbestos cement, ductile iron, reinforced concrete, and steel came into use as materials for water supply pipelines in the 20th century.

In addition to quantity of supply, water quality is also of concern. Even the ancients had an appreciation for the importance of water purity. Sanskrit writings from as early as 2000 BC tell how to purify foul water by boiling and filtering. Many ancient cities had drainage systems, but they were primarily intended to carry rainwater away from roofs and pavements. A notable example is the drainage system of ancient Rome. It included many surface conduits that were connected to a large vaulted channel, called the Cloaca Maxima (Great Sewer), which carried drainage water to the Tiber River. Built of stone and on a grand scale, the Cloaca Maxima is one of the oldest existing monuments of Roman engineering.

There was little progress in urban drainage or sewerage during the Middle Ages. Privy vaults and cesspools were used, but most wastes were simply dumped into gutters to be flushed through the drains by floods. Toilets were installed in houses in the early 19th century, but they were usually connected to cesspools, not to sewers. In densely populated areas, local conditions soon became intolerable because the cesspools were seldom emptied and frequently overflowed. The threat to public health became apparent. In England in the middle of the 19th century, outbreaks of cholera were traced directly to well-water supplies contaminated with human waste from privy vaults and cesspools. It soon became necessary for all water closets in the larger towns to be connected directly to the storm sewers. This transferred sewage from the ground near houses to nearby bodies of water. Thus, a new problem emerged: surface water pollution.

In the 20th century there has been spectacular improvement in the expectation of life in the affluent countries. This been due far more to public health measures than to curative medicine. These public health measures began operation largely in the 19th century. At the beginning of that century, drainage and water supply systems were all more or less primitive; nearly all the cities of that time had poorer water and drainage systems than Rome had possessed 1,800 years previously. Infected water supplies caused outbreaks of typhoid, cholera, and other waterborne infections. By the end of the century, at least in the larger cities, water supplies were usually safe. Insect-borne infections, such as malaria and yellow fever, which were common in tropical and semitropical climates, were eliminated by the destruction of the responsible insects. Fundamental to this improvement in health has been the diminution of poverty, for most public health measures are expensive. The peoples of the developing countries fall sick and sometimes die from infections that are virtually unknown in affluent countries.

To see how this situation developed we can look at the changes which occurred in London , England – for a variety of reasons. The situation in London as it developed through the 18th century to the modern era reflect many of the problems in developing parts of the world today. Because it is, and was, a capital city, it has well documented records so we can see what happened. Also it was in England that the connection between public health, sanitation and safe water supply first became apparent.

DEVELOPMENTS IN LONDON

In the 1200s, the City authorities did not have to worry about water supply. The water from Holywell, Clerkenwell and St Clement's Well, just north of the city walls, was, 'sweet, wholesome and clear', and in addition to other suburban springs there were, Stow tells us, wells in (every street and lane of the city). The Thames and its tributaries, the Walbrook and the Fleet were probably still fit to drink. By the thirteenth century these local supplies had become inadequate or polluted, and the citizens, following the example of monastic houses, 'Were forced to seek sweet waters abroad ... for the poor to drink, and for the rich to dress their meat'. After 1236 fresh water was carried in lead pipes from Tyburn Springs (roughly where Bond Street Station stands today) down to the hamlet of Charing, along Fleet Street and over the Fleet Bridge, climbing Ludgate hill (by gravitational pressure) to a public conduit in Cheapside. This conduit, administered by a local warden, supplied water free to all comers, and for a fee for those who wanted a private supply. Illegal 'tapping-in' inevitably took place, and a culprit caught in 1478 was paraded through the streets with a miniature conduit leaking on his head. In the fifteenth century the system was extended, partly from private bequests, with new conduits in Fleet Street, Cornhill, Gracechurch Street and elsewhere, and new supplies in Islington, and in the 1540s water was brought from springs in Hampstead, Muswell Hill, Hackney and Marylebone. Water supply provided further grounds for dispute between citizens and victuallers. In the 1330s and 1340s there were complaints to the Husting that brewers were using the Cheapside conduit for making ale, and fishmongers were washing their fish in it. The butchers were the worst offenders. They were allowed to take the entrails of animals slaughtered in the Newgate Shambles to Butchers' Bridge, a jetty overhanging the Fleet, and to clean or dump them in the river.

At that time the population of London was somewhere between 60,000 and 100,000. It increased over the next century, or so, but the onset of the Black Death in 1348 – 49 decimated the population so that by 1600 there were still only about 200,000 people living in London. Then there was then a significant rise – 575,000 by 1700 growing to 958,000 in 1801. During the nineteenth century the population exploded. By 1850 there were over 2.5 million people in the area. By 1880 this had risen to 4.3 million and by 1900 the population of London was about 6.5 million. The rapid rise in the eighteenth and nineteenth centuries resulted in gross overcrowding. Water supplies were poor and safe disposal of wastes became impossible using the systems which had served Londoners in earlier days. The result was a soaring death rate.

 

MORTALITY IN LONDON

To judge from the Bills of Mortality, nearly 40 per cent of deaths in London between 1700 and 1750, and about a third thereafter, were due to deaths among children under two years old. Of every 1,000 children born in early eighteenth-century London, over 350, perhaps 400, would be dead within two years, and fully half of all London burials throughout the century were of children. These heavy losses were not confined to the poor . In healthy Putney, Edward Gibbon lost all six of his brothers and sisters in infancy. More accurate records kept by the relatively prosperous and sober Quaker community suggest that infant mortality was even higher than the Bills of Mortality imply. Quakers lost a third of their children in their first year of life, nearly a half before they were two, and about two-thirds before their fifth birthday, between 1700 and 1775. Significant improvement came only between 1775 and 1800, when 23% of Quaker children died in their first year, and 47 per cent before they were five. In Canada today, for comparison, the infant mortality rate is less than 6 per thousand live births. In countries like Haiti the rate has fallen from 139 in 1978 to 68 in 1998.

The causes of this enormous infant death rate, and its late eighteenth-century decline, are uncertain. The ‘searchers', whose diagnoses are recorded in the Bills of Mortality, blamed about 12 per cent of infant deaths on 'teething', and around 75 per cent on 'convulsions'. This was a popular catch-all diagnosis which could cover the early stages of smallpox, and perhaps other childhood diseases, including measles, scarlet fever diphtheria and whooping cough, as well as the symptoms of gastritis, and infantile diarrhoea. Infants were especially vulnerable to gastric disorders and it is significant that the old description of these disorders, 'griping the guts', fell into disuse as the word 'convulsions' became more popular. Smallpox, one of the great eighteenth-century killers, was mainly a disease of infants and children, and most adult Londoners, unless they were migrants, had already had the disease. Well over 50 per cent of Quakers who died of smallpox between 1650 and 1800 were under five, and the disease did not often cause death among the over-thirties.

The plague was gone for good, but other infectious diseases seem to have increased in intensity in the early eighteenth century, particularly smallpox, typhus and tuberculosis ('consumption'), which probably accounted between them for about 60 per cent of non-infant death.. Typhus appears, as 'fever' or 'spotted fever', in every year's Bills of Mortality constituting about 15% of London's recorded deaths from 1700 to 1775, and 11.5% from 1775 to 1 800, and smallpox was ever-present causing about 8 per cent of recorded deaths. From time to time a particularly strong outbreak of one disease or another pushed mortality to unusual heights. There was also a seasonal pattern of tuberculosis, influenza and typhoid in the winter months when thick unwashed and louse ridden clothing was worn day after day with dysentry and diarrhoea in the summer, when flies transmitted bacteria from filth to food and water was at its most foul.

The death rate fell from 50 per 1,000 in the 1770s to 32 per 1,000 in the early 1830s, but accurate figures are only available from the 1840s, after the introduction of voluntary civil registration of births, marriages and deaths in 1837. Outbreaks of typhus, cholera, smallpox and influenza created fluctuations in mortality figures, but in general London's annual death rate was around 24 per 1,000 people between 1840 and 1870, one or two deaths per 1,000 above the national average, and below that of Manchester, Liverpool, Glasgow and most of the great European cities. Its birth rate was near the national average of 35 per 1,000, giving London a 'natural' growth rate of over 1 per cent a year. Between 1870 and 1901 London's mortality rate fell, in line with the national trend, to 17.1 per 1,000, only a fraction above the English average, but since its birth rate also fell to 29 per 1,000, its natural rate of growth remained almost unchanged. For comparison, the current gross death rate in North America is 8.6 per thousand.

The improvement in London's health was largely the result of the decline of seven infectious diseases: whooping cough and scarlet fever (specialist killers of young children), tuberculosis, typhoid, smallpox, typhus and cholera. However, between 1850 and 1900 the infant mortality average in the United Kingdom was still as high as 150 per thousand.

DRINKING WATER

Unlike today, the work of draining, policing, housing, sanitation, water supply and poor relief was left in the hands of business, local charities and other local, private or charitable agencies. Government did not generally get involved unless others had obviously failed. Water quality in London varied, depending on the source of the supply and, to some extent, the wealth of the recipient. The old system of free public conduits had fallen out of use by 1750, and Londoners who could afford the annual fee had their basement cisterns fed by one of several commercial companies. The majority, of course, relied on public standpipes carrying very intermittent commercial supplies, or water from a well or spring, and perhaps on rainwater, the Thames, or street water-sellers. A pumped supply from the Thames, powered by a great waterwheel at the northern end of London Bridge, driven by the rapid flow of the river as it squeezed through the narrow arches, had been provided by the London Bridge Waterworks since 1582, and this supply was gradually increased by the construction of extra wheels under more arches, including one on the Southwark side in 1767. By 1822, when the planned rebuilding of the bridge led to the transfer of the Company’s business to the New River Company, it was supplying 4 million gallons a day to 10,000 customers.

If the companies took an interest in new technology, it was in steam pumps to enable them to reach higher districts and the upstairs water closets of fashionable houses, and iron mains (first used by the Chelsea company in 1746) to reduce the leakage from elm pipes. There was no attempt to filter the water or protect it from pollution until the Chelsea company introduced slow sand filtration in 1829, after strong public criticism of the state of London's water. No doubt the foul supplies described in the 1820s were worse than those of the eighteenth century, because of the rapid growth of population and (after 1778) the installation of water closets (invented by Thomas Crapper) in richer houses. But even before this the Thames received all the discharges of the river Fleet, that 'nauccious and abominable sink of nastiness', and of the dumps for dung and refuse at the river's edge. London had a complex and unplanned network of sewers, which had grown piecemeal as new districts were inhabited, but these were meant to carry surface water rather than sewage, which accumulated in cesspools until the night soil men cleared it out. In practice, the inert and corrupt Commissioners of Sewers who had administered the drainage of the London area since the sixteenth century did little to protect or improve the system, and public complaints suggest that the drains carried sewage and the refuse of pigsties and slaughterhouses as well as rainwater. Perhaps it was a blessing that some of these sewers were so wide and undulating that their contents never reached the Thames.

OPINIONS ON LONDON’S WATER

Opinions differed on whether it was safe to drink London's water. Jonathan Swift (author of Gulliver’s travels) gives us this memorable picture of the liquid that flowed into the Thames, via the Fleet, after a City shower in 1710:

Now from all parts the swelling Kennels flow,

And bear their Trophies with them as they go:

Filth of all Hues and Odours seem to tell

What street they sail'd from, by their Sight and Smell.

They, as each Torrent drives, with rapid Force

From Smithfield or St Pulchre's shape their Course,

And in huge Confluent join at Snow-Hill Ridge,

Fall from the Conduit prone to Holborn-Bridge.

Sweepings from Butchers Stalls, Dung, Guts, and Blood,

Drown'd Puppies, stinking Sprats, all drench'd in Mud,

Dead Cats and Turnip-Tops come tumbling down the Flood."

Not surprisingly, Swift drank wine, because 'water is so dangerous' A visitor to London between 1725-30 noted however, that although,

"water is to be had in abundance in London, and of fairly good quality, absolutely none is drunk. The lower classes, even the paupers, do not know what it is to quench their thirst with water "

The novelist Tobias Smollett expressed his view in 1771.

"If I would drink water, I must quaff the mawkish contents of an open aqueduct, exposed to all manner of defilement, or swallow that which comes from the River Thames impregnated with all the filth of London and Westminster. Human excrement is the least offensive part … which is composed of all the drugs, minerals, and poisons used in mechanics and manufacture, enriched with the putrefying carcases of beasts and men, and mixed with the scourings of all the wash-tubs, kennels, and common sewers within the bills of mortality".

 

On the other hand a House of Commons committee in 1820, pronounced the water to be 'very superior to that enjoyed in every other city in Europe' – this only twelve years before London's first cholera outbreak

 

 

THE SANITARY QUESTION

From around 1830, national politicians and civil servants began to accept a more direct role in a wider range of urban social issues, particularly in matters of public health, poor relief and factory conditions. Although public attitudes towards government intervention were slowly becoming more favourable, it usually took a well-publicised crisis or disaster to awaken aristocratic politicians to an awareness of their new social responsibilities. The arrival of cholera, a dramatic bacterial infection of the gut previously unknown in Europe, whose westward progress had been watched with dread since it appeared in India in 1818, was such a crisis. Cholera reached Britain in October 1831 and London in February 1832, and killed over 31,000 in Great Britain (5,000 in London) by a process of rapid and painful dehydration. The devastating impact of this new disease, its dramatic impact on its victims, and fears that it might be the new plague, forced politicians to act.

Unfortunately, ignorance of the causes of cholera meant that the response to it was often ineffective and sometimes harmful. Cholera was transmitted by the ingestion of the faeces of infected people, sometimes from contaminated food or clothing, but most often from sewage-polluted water. It thus entered London households in buckets and pipes. Six of London's eight piped-water companies took their supplies from the Thames. Only two, the New River Company and the East London Company, got theirs wholly or mainly from the Lea. Piped water was dirty enough in the first place, but since supplies were intermittent and did not run on Sundays until 1872, most consumers stored water in cisterns or tubs, in which it became filthier still. Poorer families, who had to fetch water from street stand pipes, often preferred to fill their buckets from the pump of a local well, to dip them into the Thames, the Wandle, the Regent's Canal, or some other convenient and tasty source. The Thames, sadly for the millions of Londoners who drank from it, was as much liquid biology as it was liquid history. As Sydney Smith, canon of St Paul's, wrote to a friend 1834, 'he who drinks a tumbler of London water has literally in his stomach more animated beings than there are men, Women and Children on the face of the Globe'. At least 140 sewers discharged their contents (which contained an increasing proportion of household sewage) into the Thames in 1828, and the growing use of flush toilets in the 1830s and 1840s meant that the problem got much worse by the middle of the century.

The deterioration of the Thames water was clearly noticeable by the 1820s and two Government reports had suggested that London should find a new unpolluted source, or that the water companies that drew their water from the Thames should use sand filters to purify their supplies. But orthodox medical belief was that diseases were spread by contagion. The newer view, which became official dogma asserted the infectious agency of bad air, or 'miasma', arising from animal or vegetable putrefaction. Government policy in 1832, reacting in panic to the arrival of cholera, combined the advice of both schools of thought. It revived the old plague quarantine measures, and also ordered makeshift local Boards of Health to flush sewers, empty cesspools, cart away piles of rubbish and dung, and cleanse slaughterhouses and infect homes. Meanwhile the true source of infection, the reeking Thames, was made filthier still by the efforts of the Boards.

The 'sanitary' interpretation of disease, which emphasised foul urban conditions and putrefying matter as the main removable cause of ill health began to dominate public medical policy after 1832. However, as late as 1847 thousands of houses still relied on a few filthy privies, emptying into around 5,000 cesspools, many of them overflowing. Rubbish piles, foul slaughterhouses, noxious workshops, overflowing graveyards and standpipes running for only a few minutes a day were common throughout London – at a time when the Lord Mayor claimed that the City’s sanitation was "perfect".

The situation improved slowly. A City Sewers Act was passed in 1848 but water supply was still left in private hands. In 1849 cholera struck again and killed 854 people in the City of London (i.e. central London, not the Metropolitan area). In response another sewers act was passed in 1851 but another Cholera epidemic occurred in 1854 and 10,738 Londoners died.

In 1849 Drs William Budd and John Snow had suggested that cholera was spread by the swallowing of its living organism in drinking water. Comparison of death rates in 1848 in parts of South London served by two different water companies was used to support their argument. Most authorities, dismissed the idea, but in 1854 Snow proved his point by his study of the disastrous outbreak in Soho, between Regent Street, Wardour Street, Brewer Street and Great Marlborough Street. Snow was able to show that the bulk of the 500 people who died in this small district drew their water from a well in Broad Street, while users of local wells had escaped. Once the pump was sealed off, the outbreak subsided. Legend has it that Dr Snow, himself, removed the handle to the pump when the authorities refused to act. A later study, in 1856, showed that customers of the Lambeth Water Company, whose water came from a relatively unpolluted source, had a death rate in 1854 of only 37 per 10,000, compared with a rate of 130 per 10,000 for those who drank the Southwark and Vauxhall's filthy supplies from Battersea. In 1848-9, before the Lambeth Company moved its source upstream, there had been little disparity between the two rates. Despite this evidence it still took another ten years for the medical community to accept that cholera was water-borne.

In 1855, The metropolitan Board of Works was formed for "the better management of the metropolis in respect of sewerage and drainage and the paving, cleansing, lighting and improvements thereof". The urgent task of the Board was to construct "a system of sewerage which should prevent all or any part of the sewage within the metropolis from passing into the Thames in or near the metropolis". For three years little was done; then, on 30 June 1858, panic broke out in the House of Commons. The cause was 'the great stink', arising off the Thames (called by Disraeli 'a Stygian pool'). The windows of the Houses of Parliament had to be hung with sheets soaked in chloride of lime, and tons of lime were daily dumped into the river. The stench forced the House to adjourn. That settled matters. Laissez-faire dogmatists hardened to 10000 cholera cases in Whitechapel rushed a Bill through Parliament to confer the necessary powers upon the Metropolitan Board of Works. The Board's Chief Engineer, Sir Joseph Bazalgette, set about creating a grand scheme which, completed in 1875 at a cost of £6.5 million, still serves, in part, today. His task was helped by the fact that, though the scientific causes of epidemics were still hotly disputed, consensus had emerged that poor sanitation - above all, contamination of drinking-water by sewage - was a deadly threat. Today we know that threat extends far beyond only cholera and that many diseases – particularly in poor communities - are linked in some way to polluted water and poor sanitation. Many parts of the developing world suffer from the problems that London experienced in the 1800s

 

WATER AND DISEASE

Diseases involving water are known as "water related diseases". They fall into a number of different categories.

  1. Waterborne diseases occur when the pathogen is in water which is drunk by the person who may then become infected. Such diseases include Cholera, Typhoid and a wide range of others such as infectious hepatitis and various diarrhoeal diseases and dysentery.
  2. Water Washed Diseases occur because of poor hygiene and may be eliminated by an increase in the quantity of water available. There are three main types of water washed disease – intestinal tract infections (because of the faecal – oral route but not by drinking), and skin and eye diseases such as scabies or trachoma. These are related to poor hygiene and may be reduced by providing more water for personal cleanliness.
  3. Water based diseases are ones in which the pathogen spends part of its life cycle in water – e.g. in water snails. These are usually caused by parasitic worms or similar. Diseases include schistosomiasis, guinea worm etc
  4. Water Related Insect Vector diseases . In this type of disease the infection is spread by an infected insect which spends part of its life cycle in the water. If the insect can be eliminated the pathogens cannot access human beings. These diseases include – Malaria, Sleeping sickness, River blindness, Yellow Fever, Dengue fever and others.

 

The primary water related diseases are described below

Typhoid: (waterborne) acute infectious bacterial disease usually caused by ingestion of the bacterium through the mouth. After 10 – 14 days the patient experiences headache, lassitude, fever and diarrhoea. In the second week, bleeding from the bowel occurs with various complications. After four weeks there may be recovery but with no treatment there is about 25% mortality.

Cholera: (waterborne) acute bacterial infection of lower bowel leading to massive diarrhoea and loss of body fluids and salts. Fifteen to twenty litres of fluid may be lost in 24 hours. Mortality is high but can be greatly reduced by fluid and salt replenishment. The disease runs its course in about two to seven days.

Dysentery and other diarrhoeal diseases: (waterborne) are typically caused by protozoa or bacteria and result in large loss of fluids and salts. Outbreaks are almost always related to fecal contamination of water supplies.

Schistosomiasis: (water based) – also called bilharzia - is caused by small parasitic flatworms which live in the blood vessels and release eggs which cause tissue damage. The eggs get into the intestine or bladder and are then released in faeces or urine. On contact with fresh water the eggs hatch, releasing larvae which find their way into water snails. The larvae subsequently emerge from the snail and bore their way through the skin of any nearby mammal in the water. The worms cause great lassitude and may cause serious liver damage. The disease is probably, next to malaria, the worlds most serious parasitic infection.

Malaria: (insect vector) is one of the most ancient diseases known and occurs throughout the tropical and subtropical areas. It is generally uncommon in temperate regions. The disease is caused by various species of protozoa which are transmitted by the anopheline mosquito, known as the vector. The mosquito transmits the disease by feeding on infected people. The development of mosquitoes requires a larval stage in which the larvae grows in fresh, stagnant, water so many communities attempt to control the spread of the disease by eliminating or spraying any areas of standing water in urban areas. The disease is endemic in Africa where it is estimated that it causes the death of a child every 20 seconds.

Yellow Fever and Dengue Fever are, similarly, transmitted by (different) mosquito vectors. Dengue fever has increased from about 30,000 cases per year in 1960 to over 590,000 cases per year in 1995. The cause is not fully understood but is thought to relate to urbanisation and its many opportunities for mosquito breeding.

 

THE SITUATION TODAY

At the turn of the century, Typhoid was still a serious infectious disease in America with a death rate of about 31 per 100,000 in 1900. This would be equivalent to metropolitan St John’s experiencing over 60 deaths per year – each year. Today it is of minimal concern in North America but epidemic outbreaks can still occur.

In 1991, an epidemic of cholera started in Peru and spread to the rest of Latin America. This epidemic reached the U.S. in 1992 via an outbreak among 75 commercial airline passengers from Peru. The epidemic is reported to have caused as many as 1 million cases of cholera and as many as 10,000 deaths.

Although the epidemic was reportedly started by a ship which dumped its bilge water within reach of Peruvian waters, the epidemic's spread has been credited in part to the Peruvian government's decision to stop chlorinating drinking water supplies. This decision was based on EPA studies from the 1970s that associated drinking water chlorinated to 10 parts per billion with an increase in cancer risk for individuals on the order of 1 in 10,000. The problem with chlorination is the formation of THMs – Tri Halo Methanes - which form when chlorine is added to water as a disinfectant. The chlorine reacts with organic material in the water – eg material which causes colour, taste and smell – very prevalent in Newfoundland pond water. The basic solution to the problem of THMs is to take out the organic matter before adding chlorine – possibly by filtration or by flocculation and primary sedimentation – not to stop disinfecting supplies.

Conditions throughout the world are such that every year ( 1996 data) more than five million people die from illness related to unsafe drinking water, unclean domestic arrangements and poor sanitary practice. It is estimated that perhaps one half of the people in the developing world are suffering from one or more of the diseases associated with water supply and sanitation. Estimates of morbidity ( episodes per year) and mortality ( deaths per year) for some of the major diseases are given below.

In the 1970s the United Nations proclaimed the years 1981 to 1991 to be The International Drinking Water Decade . The intention was to significantly improve drinking water supplies throughout the world and especially in the poorest areas where the quality was the least. Action was urgently needed because about 100 million more third world people were drinking dirty water in 1981 than in 1975.

 

 

 

Disease

Morbidity

Mortality

Diarrhoeal Diseases

1,000 million

3.3 million

Helminth Infection

1,500 million

100,000

Schistosomiasis

200 million

200,000

Malaria

400 million

1.5 million

Dengue fever

1.75 million

20,000

 

 

During the International Drinking Water Supply and Sanitation Decade (1981-1990), some 1600 million people were served with safe water and about 750 million with adequate excreta disposal facilities. However, because of population growth of 800 million people in developing countries, by 1990 there remained a total of 1015 million people without safe water and 1764 million without adequate sanitation.. In 1992, WHO concluded its monitoring of the Decade with the estimate that a total of US$ 133.9 billion had been invested in water supply and sanitation during the period 1981- 1990, of which 55% was spent on water and 45% on sanitation. Urban areas received 74% of the total and rural areas only 26%. Contrary to widespread perceptions, almost two- thirds of all funds were provided by national sources and only a third by external sources.

Overall progress in reaching the unserved has been poor since 1990. Approximately one billion people around the world still lack safe water and more than two billion do not have adequate excreta disposal facilities. Rapid population growth and lagging rates of coverage expansion has left more people without access to basic sanitation today than in 1990.

Another problem with coverage goals is the magnitude of resources needed to achieve them. At the Global Consultation of Safe Water and Sanitation for the 1990s, held in New Delhi in 1990, it was stated that universal coverage by the year 2000 would require expenditure of US$ 50 billion per year. Despite the size of the amount, this is still much less than the $87.5 billion per year spent on cigarettes or $511 billion spent on arms (1980 data).

 

 

 

Water Availability

WHO states that population increases and deterioration of water quality – which is most marked in the developing world – is such that the per capita availability of clean water will decrease significantly. And yet there is plenty of water for all as shown below.

LOCATION

VOLUME

(103 km3)

PERCENT OF

TOTAL

RENEWAL

TIME (years)

Oceans

1,370,000

97.61

3,100

Polar Ice, glaciers

29,000

2.08

16,000

Ground Water

4,000

0.29

300

Fresh Water Lakes

125

0.009

1-100

Saline Lakes

104

0.008

10-1000

Soil moisture

67

0.005

0.76

Rivers

1.2

0.00009

0.04

Atmospheric Water

14

0.0009

0.02

 

The table above shows the water availability in the world. Unfortunately, some places get too much and some too little. Between 1990 and 1998, for example, floods resulted in 38,000 deaths and damage estimated at US $250 billion yet one third of the worlds population lives in countries which experience moderate to high water stress. On a global basis water consumption rose six-fold between 1900 and 1995. Canada, Norway and Sweden are currently the only countries in the world where there is no vulnerability to water scarcity. Low income nations are the most vulnerable.

The prevalence of disease is increasing world-wide and environmental degradation is definitely a cause. A recent study by the UN the World Bank and the World Resources Institute says that in the poorest areas of the world, one child in five will die because of environmental degradation. On a world wide basis researchers found that one quarter of disease is linked to poor water and sanitation, disease spread by rodents and insects, and indoor and outdoor air pollution. The results include

Almost four million children who die of acute respiratory infections due to air pollution

About 21/2 million children who die from diarrhoeal diseases linked to poor water and sanitation

As many as five million people who suffer from acute pesticide poisoning

Over the last twenty years there has been considerable effort to improve water supplies and sanitation in the developing world. Much of this has involved what is known as appropriate technology. There is little benefit of installing technology using capital grants if the community involved cannot maintain and repair the equipment. Most villages in the third world are small and poor. Per capita incomes may be as little as $300 per annum. People there need systems which are inexpensive to maintain and which can be repaired using local skills with no imported expertise or equipment.

Simple systems for collecting and storing water are being developed, and installed, the emphasis being on low capital cost and easy maintenance while ensuring a safe supply. Natural systems of filtration coupled with protection of the stored water from parasites and faecal contamination have been widely used. Rainwater harvesting is popular in some areas. Some of these systems are shown in the accompanying figures. At the same time considerable effort has been devoted to the development of safe rural sanitation, again using simple systems. Pour-flush latrines with a water trap have been built in many villages , composting toilets are available and, in more advanced places, there are septic tanks and biogas systems. In these the gas given off by decomposing wastes is used to fuel cooking stoves. Some of these are also shown in the attached diagrams.

Finally the changes which have been most recently documented are shown in the table attached describing health indicators and changes in safe water and access to sanitation over the years 1982 to 1996. The plots of these data show clearly the link between disease and water. They also show that the percentage of people with access to safe water and good sanitation is increasing. Unfortunately, the rapid population growth in the developing world means that, on an absolute basis, there are more people today without access than was the case in 1990. Then it was estimated that there were 1015 million people without safe water and 1764 million without adequate sanitation. The situation is worse today.

SOURCES

Agarwal et al, "Water Sanitation and Health for All", Earthscan, 1980.

Encyclopaedia Britannica (on the web

Inwood, S., "A History of London", Macmillan, London, 1998

Dangerfield, B.J., Ed., "Water Supply and Sanitation in Developing Countries" Inst. of Water Engineers and Scientists, London, England, 1983.

Ponter, R., "London – a Social History", Harvard Univ. Press, Cambridge, Ms, 1995

Sheppard, F., "London – a History", Oxford Univ Press, 1998, Oxford, England.

Welsh, Brian W.W. and P. Butorin, " Dictionary of development : Third world economy, environment, society", : Garland, New York 1990.

World Resources Inst., UNEP, UNDP and the World Bank, "World resources 1998-99", Oxford University Press, 1998

World Bank ,"World Development Indicators 2000", CD ROM, IBRD, World Bank, Washington, 2000

 

 

 

 

 

 

 

 

 

 

 

APPENDIX 1 DATA SHEETS

 

 

World Bank

 

Safe

Life exp.

Infant

Access to

 

Acces

 

data

 

Water

at birth

mortality

Safe water

 

To

 
   

% of

       

Sanitn.

 
 

population

population

 

per 1,000

% of

 

% of

 
 

thousands

with access

years

live births

population

 

population

 

country

1998

1990-96 /a

1998

1998

1982-85a

1990-96a

1982-85a

1990-96a

Finland

5,153

98

77

4

95

98

100

100

Japan

126,410

96

81

4

99

96

99

100

Norway

4,432

100

78

4

99

100

 

100

Singapore

3,164

100

77

4

100

100

85

100

Switzerland

7,106

100

79

4

100

100

 

100

Australia

18,751

99

79

5

99

99

99

86

Canada

30,301

99

79

5

100

99

85

95

France

58,847

100

78

5

98

100

 

96

Italy

57,589

78

5

99

   

100

Netherlands

15,698

100

78

5

100

100

 

100

Slovenia

1,982

98

75

5

 

98

80

98

Ireland

3,705

76

6

97

   

100

Israel

5,963

99

78

6

100

99

 

100

United Kingdom

59,055

100

77

6

100

100

 

100

Cuba

11,103

93

76

7

82

93

 

88

Croatia

4,501

63

73

8

 

63

67

61

Malaysia

22,180

89

72

8

71

89

75

94

Portugal

9,968

82

75

8

66

82

 

100

United Arab Emirates

2,724

98

75

8

100

98

86

95

Korea, Rep.

46,430

83

73

9

83

83

100

100

Chile

14,822

85

75

10

86

85

67

 

Puerto Rico

3,860

97

76

10

 

97

   

Kuwait

1,866

100

77

12

100

100

100

100

Costa Rica

3,526

92

77

13

 

92

95

97

Barbados

266

100

76

14

       

Ukraine

50,295

55

67

14

 

55

 

49

Sri Lanka

18,778

46

73

16

37

46

 

52

Trinidad and Tobago

1,285

82

73

16

98

82

 

96

Uruguay

3,289

89

74

16

83

89

59

61

Moldova

4,298

56

67

18

 

56

 

50

Oman

2,302

68

73

18

58

68

39

85

Argentina

36,125

65

73

19

55

65

69

75

Mauritius

1,160

98

71

19

99

98

97

100

Saudi Arabia

20,739

93

72

20

91

93

86

86

Jamaica

2,576

70

75

21

96

70

91

74

Panama

2,764

84

74

21

82

84

81

90

Romania

22,503

62

69

21

71

62

 

44

Venezuela, RB

23,242

79

73

21

84

79

45

58

Uzbekistan

24,051

57

69

22

 

57

 

18

Colombia

40,804

78

70

23

 

78

68

83

Libya

5,302

90

70

23

90

90

70

86

Tajikistan

6,115

69

69

23

 

69

 

62

Albania

3,339

76

72

25

92

76

 

58

Paraguay

5,219

39

70

24

23

39

49

32

Iran, Islamic Rep.

61,947

83

71

26

71

83

65

67

Kyrgyz Republic

4,699

81

67

26

 

81

   

Jordan

4,563

89

71

27

89

89

91

95

Lebanon

4,210

100

70

27

92

100

75

100

Syrian Arab Republic

15,277

85

69

28

71

85

45

56

Tunisia

9,335

99

72

28

89

99

52

96

Thailand

61,201

89

72

29

66

89

47

96

Mexico

95,846

83

72

30

82

83

57

66

China

1,238,599

90

70

31

 

90

 

21

El Salvador

6,058

55

69

31

51

55

62

68

Ecuador

12,175

70

70

32

58

70

57

64

Philippines

75,174

83

69

32

65

83

57

77

Brazil

165,874

72

67

33

75

72

24

67

Turkmenistan

4,718

60

66

33

 

60

 

60

Vietnam

76,520

36

68

34

 

36

 

21

Honduras

6,156

65

69

36

50

65

32

65

Nicaragua

4,794

81

68

36

50

81

27

31

Dominican Republic

8,254

71

71

40

49

71

66

78

Peru

24,801

80

69

40

53

80

48

44

Guatemala

10,799

67

64

42

58

67

54

67

Indonesia

203,678

62

65

43

39

62

30

51

Egypt, Arab Rep.

61,401

64

67

49

90

64

 

11

Morocco

27,775

52

67

49

32

52

50

40

South Africa

41,402

70

63

51

 

70

 

46

Guyana

849

81

64

57

       

Papua New Guinea

4,603

28

58

59

 

28

 

22

Bolivia

7,950

55

62

60

53

55

36

41

Eritrea

3,879

7

51

61

 

7

   

Botswana

1,562

70

46

62

 

70

36

55

Ghana

18,460

56

60

65

 

56

26

42

Namibia

1,662

57

54

67

 

57

 

34

Senegal

9,039

50

52

69

44

50

 

58

Sudan

28,347

50

55

69

 

50

5

22

India

979,673

81

63

70

54

81

8

16

Haiti

7,647

28

54

71

 

28

19

24

Bangladesh

125,629

84

59

73

40

84

4

35

Zimbabwe

11,689

77

51

73

52

77

26

66

Gambia, The

1,216

76

53

76

45

76

 

37

Kenya

29,295

53

51

76

27

53

44

77

Nigeria

120,817

39

53

76

36

39

 

36

Cameroon

14,303

41

54

77

36

41

36

40

Nepal

22,851

44

58

77

24

44

1

6

Myanmar

44,464

38

60

78

27

38

24

41

Togo

4,458

63

49

78

35

63

14

26

Yemen, Rep.

16,599

39

56

82

 

39

 

19

Tanzania

32,128

49

47

85

52

49

 

86

Gabon

1,180

67

53

86

 

67

50

76

Benin

5,948

50

53

87

14

50

10

20

Côte d'Ivoire

14,492

72

46

88

20

72

17

54

Congo, Dem. Rep.

48,216

27

51

90

 

27

 

9

Congo, Rep.

2,783

47

48

90

 

47

 

9

Mauritania

2,529

64

54

90

37

64

 

32

Pakistan

131,582

60

62

91

38

60

16

30

Madagascar

14,592

29

58

92

31

29

 

15

Lesotho

2,058

52

55

93

18

52

12

6

Lao PDR

4,974

39

54

96

 

39

 

24

Central African Republic

3,480

19

44

98

 

19

19

46

Chad

7,283

24

48

99

 

24

14

21

Uganda

20,897

34

42

101

16

34

13

57

Cambodia

11,498

13

54

102

 

13

   

Iraq

22,328

44

59

103

74

44

 

36

Ethiopia

61,266

27

43

107

 

27

 

8

Zambia

9,666

43

43

114

48

43

47

23

Mali

10,596

37

50

117

 

37

21

31

Burundi

6,548

52

42

118

23

52

 

51

Guinea

7,082

62

47

118

20

62

12

14

Niger

10,143

53

46

118

37

53

9

15

Angola

12,001

32

47

124

28

32

18

16

Guinea-Bissau

1,161

53

44

128

31

53

 

20

Malawi

10,534

45

42

134

32

45

60

53

Mozambique

16,947

32

45

134

9

32

10

21

Sierra Leone

4,855

34

37

169

24

34

13

11

 

 

 

APPENDIX 2 – THE STORY OF JOHN SNOW

John Snow (1813 - 1858), an anaesthesiologist, conducted a series of investigations in London that later earned him the title 'the father of field epidemiology." Twenty years before the discovery of the microscope, Snow conducted studies of cholera outbreaks to discover the cause of the disease and to prevent its recurrence. His work classically illustrates the sequence from descriptive epidemiology to hypothesis generation to hypothesis testing to public health application. Snow conducted his study in 1854 when an epidemic of cholera developed in the Golden Square of London. He began his investigation by determining where in this area persons with cholera lived and worked. He then used this information to map the distribution of cases on what epidemiologists call a spot map. His map is shown below. Because Snow believed that water was a source of infection for cholera, he marked the location of water pumps on his spot map, and then looked for a relationship between the distribution of cholera case households and the location of pumps. He noticed that more case households clustered around the Broad Street pump (Pump A) than around Pumps B or C, and he concluded that the Broad Street pump was the most likely source of infection. Questioning residents who lived near the other pumps, he found that they avoided Pump B because it was grossly contaminated, and that Pump C was located too inconveniently for most residents of the Golden Square area. From this information, it appeared to Snow that the Broad Street pump was probably the primary source of water for most persons with cholera in the Golden Square area. He realised, however, that it was too soon to draw that conclusion because the map showed no cholera cases in a two-block area to the east of the Broad Street pump. Perhaps no one lived in that area. Or perhaps the residents were somehow protected.

Upon investigating, Snow found that a brewery was located there and that it had a deep well on the premises where brewery workers, who also lived in the area, got their water. In addition, the brewery allotted workers a daily quota of malt liquor. Access to these uncontaminated rations could explain why none of the brewery's employees contracted cholera. To confirm that the Broad Street pump was the source of the epidemic, Snow gathered information on where persons with cholera had obtained their water. Consumption of water from the Broad Street pump was the one common factor among cholera patients. According to legend, Snow removed the handle of that pump and aborted the outbreak.

Snow's second major contribution involved another investigation of the same outbreak of cholera that occurred in London in 1854. In a London epidemic in 1849, Snow had noted that districts with the highest mortalities had water supplied by two companies: the Lambeth Company and the Southwark and Vauxhall Company. At that time, both companies obtained water from the Thames River at intake points that were below London. In 1852, the Lambeth Company moved their water works to above London, thus obtaining water that was free of London sewage. When cholera returned to London in 1853, Snow realised the Lambeth Company's relocation of its intake point would allow him to compare districts that were supplied with water from above London with districts that received water from below London.

The data Snow collected showed that the risk of death from cholera was more than 5 times higher in districts served only by the Southwark and Vauxhall Company. Interestingly, the mortality rate in districts supplied by both companies falls between the rates for districts served exclusively by either company. These data were consistent with the hypothesis that water obtained from the Thames below London was a source of cholera. Alternatively, the populations supplied by the two companies may have differed in a number of other factors which affected their risk of cholera.

To test his water supply hypothesis, Snow focused on the districts served by both companies because the households within a district were generally comparable except for their water supply company. In these districts, Snow identified the water supply company for every house in which a death from cholera had occurred during the 7-week period. He found the highest incidence of the disease in the households served by polluted water.

This additional study added support to Snow's hypothesis, and demonstrates the sequence of steps used today to investigate outbreaks of disease. Snow developed a testable hypothesis based on a characterisation of the cases and population at risk by time, place, and person. He then tested this hypothesis with a more rigorously designed study, ensuring that the groups to be compared were comparable. After this study, efforts to control the epidemic were directed at changing the location of the water intake of the Southwark and Vauxhall Company to avoid sources of contamination. Thus, with no knowledge of the existence of micro-organisms, Snow demonstrated through epidemiologic studies that water could serve as a vehicle for transmitting cholera and that epidemiologic information could he used to direct prompt and appropriate public health action.

 

Much of this appendix is adapted from Centres for Disease Control and

Prevention, Principles of epidemiology: An introduction to applied epidemiology and biostatistics,

2d ed. Atlanta, GA: Centres for Disease Control and Prevention, 1992.

APPENDIX 3. THE RECENT CHOLERA EPIDEMIC

 

In 1991, a cholera epidemic swept down the west coast of South America - the first such outbreak in nearly a century in the New World. Between 1991 and 1995, a disease long thought to have been vanquished in the Americas had infected more than 1 million people and killed 11,000. Africa experienced a similar cholera surge in 1991, with the number of cases rising fourfold in a single year (from 38,683 in 1990 to 153,367 in 1991) and deaths mounting to 14,000. Three years later, the cholera epidemic hit Russia and cholera cases jumped from just 23 the year before to 1,048.

Why has cholera re-emerged as a global health threat, after virtually disappearing from the Americas and most of Africa and Europe for more than a century? The answer may lie in how changing environmental conditions from both natural and human causes can affect the spread of an infectious disease.

Cholera is generally spread by contact with water or food contaminated with human waste containing cholera bacteria. That is why the disease has long been associated with the unsanitary conditions often found in urban slums, or in connection with war, natural disasters, and other dislocations. But cholera also has a traditional link with the sea. In nature, the cholera organism (Vi- brio cholerae) thrives best in moderately salty waters such as coastal estuaries, though it can also tolerate the open ocean. It generally only inhabits rivers and other freshwater sources if nutrient levels from organic pollution such as human faeces are quite high.

These two environmental links-with the sea and with unsanitary conditions-do much to explain the pattern of cholera epidemics throughout history. Global epidemics (pandemics) of cholera often hit first in coastal cities and have clearly been associated with unhygienic conditions. Originally restricted to the Indian subcontinent, cholera spread from India to Europe between 1817 and 1823, launching the first global cholera pandemic. Since then, six more pandemics have washed, wavelike, across the continents, receding for a time between each pulse.

By the end of the 19th Century, cholera appeared to retreat as a global health threat. After 1900, it disappeared from the Americas and most of Europe; and by 1950 it was largely confined to the Indian subcontinent, where it had originated, and the Asian countries west of India. But in 1961, a new pulse of the disease-the seventh pandemic-began to spread from Asia, eventually emerging with a vengeance in 1991 in Latin America and Africa. Though this latest pandemic has peaked, the disease remains endemic throughout these regions.

Part of the blame for the dramatic rise in cholera cases in Latin America and Africa rests with obvious causes: deteriorating water and sanitation systems, poor living conditions, malnutrition, crowding, and political and economic turmoil. For example, studies of the 1991 cholera epidemic in Peru suggest that the lack of effective water treatment measures contributed to the rapid spread of the disease. Engineers of the public water supply system in the coastal city of Trujillo believed that no water treatment would be necessary. The fear of the carcinogenic risk associated with chlorine disinfection by-products superceded the fear of cholera infection. And, testimony of health workers in Iquitos, a jungle city in Peru, suggests that even home- based chlorination could have been key in arresting further dissemination of the disease. Rapid population growth and lack of investment in public services had led to serious declines in Lima's sanitation coverage, and between 5 million and 6 million city residents had no access to acceptable latrines. In Africa, civil strife and drought in the 1980s had led to unusually large migrations and concentrations of people in urban slums and refugee camps. About 50,000 Rwandan refugees contracted cholera in such camps after the 1991 outbreak, and many thousands died. Other factors played a role as well in cholera resurgence. Some cholera cases in Latin America were traced to the growing use of wastewater to irrigate crops near urban areas. In addition, food-handling practices, especially by street vendors, may have added to the global outbreak. Street vendors are a central feature of poor urban communities throughout the developing world, but their lack of refrigeration and clean water often increases the risk of contamination. In Latin America, uncooked seafood was also an important route of cholera transmission because seafood is often caught or processed in unhygienic conditions .

But these factors don't fully explain how cholera re-emerged in Latin America so suddenly after more than a century's absence. Moreover, the 1991 pandemic struck nearly simultaneously over a wide area, appearing in ports from the Chilean to the Ecuadorean border within a few weeks. What event or series of events had so effectively reintroduced cholera over huge stretches of open coastline?

One possibility is that the cholera organism was carried by ship from Asian to Latin American ports in ballast water-a well known vehicle for transporting foreign organisms, ranging from microscopic bacteria and viruses to mollusks and small crabs. DNA testing of the Latin American cholera strain shows that it is genetically similar - although not identical - to a cholera strain common in Bangladesh, and this strain has been isolated in samples of ballast, bilge, and sewage from cargo ships active in the area. Still, the speed with which the epidemic spread to points so widely dispersed casts some doubt on whether shipping traffic alone can explain the disease's re-emergence

A second theory is that cholera never really disappeared from the Americas at all, but merely went into a dormant, non-infective state in coastal waters, from which it re-emerged when the right combination of favourable environmental conditions appeared. Evidence for this theory of ocean waters as a reservoir of cholera comes from the recent discovery that some species of plankton can act as hosts for the dormant cholera organism. This allows the organism to persist in coastal waters for long periods, and then to "reappear" after years of seeming absence. This theory also helps explain why cholera epidemics in Bangladesh occur seasonally, often coinciding with plankton blooms in the Bay of Bengal.

The cholera-plankton connection probably also offers the disease a means of long-distance travel, hitchhiking with the plankton on ocean currents across thousands of kilometres and over periods of months and years. This might explain how an Asian cholera strain could find its way to several points along the coast of South America without stowing away in ballast water.

El Nino, a periodic change in weather patterns that can profoundly affect local environmental conditions, may also have played a key role in cholera’s return. El Nino heats surface water currents that start in the eastern Pacific Ocean near the coast of Central and South America and then spread throughout the tropics and subtropics. The warm sea surface temperatures that El Nino brings can encourage large plankton blooms, especially in coastal waters with high levels of nutrients from sewage and storm water runoff. These blooms can awaken the cholera organism, bringing it back to its infectious state. The Latin American cholera epidemic occurred in tandem with the coming of the last El Nino, which began in 1991 and lasted until mid 1995 - the longest El Nino on record .

Cholera’s dependence on environmental factors such as sea surface temperatures, nutrient levels in coastal waters, and plankton blooms may have some important implications for the future of the disease. For one, the frequency of plankton blooms is increasing world wide and is likely to rise even more in the future due to a combination of factors. These include higher ocean temperatures from global warming, increased nutrient runoff from expanding urban populations, and an additional plankton fertilising effect from high carbon dioxide levels in the atmosphere. More frequent plankton blooms will very likely put more coastal areas at risk of cholera outbreaks. This means that tackling urban poverty and providing for adequate water and sanitation services - the front lines in the fight against cholera - will only become more important in the years ahead.

 

 

This appendix is copied from "World Resources 1998 – 99"