Microbiological Aspects of BIOFILMS and DRINKING WATER - Chapter 3 ppsx

39 3.1 WATERBORNE DISEASE AND ITS EPIDEMIOLOGY Since John Snow proved that drinking water could transmit cholera, many diseases have been shown to be spread by water.. The World Health O

Trang 1

0-8493-????-?/97/$0.00+$.50

CONTENTS

3.1 Waterborne Disease and its Epidemiology 29

3.2 Reported Outbreaks of Waterborne Disease 32

3.3 Epidemiological Studies of Waterborne Disease 37

3.4 References 39

3.1 WATERBORNE DISEASE AND ITS EPIDEMIOLOGY

Since John Snow proved that drinking water could transmit cholera, many diseases have been shown to be spread by water Estimates vary widely as to the actual morbidity and mortality owing to waterborne disease The World Health Organiza-tion (WHO) estimates that every 8 seconds a child dies from a water-related disease and each year more that 5 million people die from illnesses linked to unsafe drinking

disease associated with water-associated disease While the figures in this table seem alarming, the situation is likely to deteriorate substantially as the world population continues to increase The WHO also suggests that if sustainable safe drinking water and sanitation services were provided to all, each year there would be

200 million fewer diarrhoeal episodes

2.1 million fewer deaths caused by diarrhoea

76,000 fewer dracunculiasis cases

150 million fewer schistosomiasis cases

75 million fewer trachoma cases

There are four ways by which water, or the lack of it, may be associated with

by human or animal faeces or urine containing pathogenic bacteria or viruses It includes cholera, typhoid, amoebic and bacillary dysentery, and other diarrhoeal diseases

or eye contact with contaminated water It includes scabies, trachoma, and flea, lice, and tick-borne diseases

organisms living in water It includes dracunculiasis, schistosomiasis, and other helminths

water It includes dengue, filariasis, malaria, onchocerciasis, trypanosomi-asis, and yellow fever

0590/frame/ch03 Page 29 Tuesday, April 11, 2000 12:02 PM

Trang 2

30 Microbiological Aspects of Biofilms and Drinking Water

In this book, we are primarily concerned with waterborne disease transmitted

drinking water and describes some of the symptoms that they cause For a more

TABLE 3.1

Estimates of Morbidity and Mortality of Water-Related Diseases

Disease

Morbidity (Episodes/Year,

or as Stated)

Mortality (Deaths/Year)

Relationship of Disease

to Water Supply and Sanitation

Diarrhoeal

diseases

disposal, poor personal and domestic hygiene, unsafe drinking water Infection with

intestinal

helminths

disposal, poor personal and domestic hygiene

disposal and absence of nearby sources of safe water

often owing to absence of nearby sources

of safe water

storage, operation of water points, and drainage

water storage, operation of water points, and drainage

personal and domestic hygiene, and unsafe drinking water

safe water Bancroftian

filariasis

storage, operation of water points, and drainage

large-scale projects

1 People currently infected.

Trachoma occur annually.

Source: WHO data.

Trang 3

Waterborne Diseases 31

TABLE 3.2

Microbial and Parasitic Disease Linked to Drinking Water Consumption

Usual Incubation

medinensis

(Prev G lamblia)

bloating and flatulence; for more prolonged disease, weight loss and failure to thrive

parvum

weeks

cayetanensis

vomiting, and anorexia; weight loss

in prolonged cases

fulminating dysenteric illness

pregnant women, can cause damage

to foetus including abortion, hydrocephalus, cerebral calcification, and eye damage

severe cases can lead to dehydration, shock, and death

and fever; may progress to more severe systemic disease in a small proportion of cases

as disease progresses may develop delerium; untreated death rate is up

to 15%

diarrhoea to more severe diarrhoea with painful straining to empty bowels, blood loss leading to collapse and death

cramping abdominal pain Enterotoxigenic

E coli

E coli 12–72 hours Watery diarrhoea Enterohaemorrhagic

E coli

E coli 0157 and others 3–4 days Bloody diarrhoea which can be fatal

and progress to haemolytic uraemic syndrome in children

continued

Trang 4

For the rest of this chapter, we shall consider the question of how common is disease caused by potable water We shall restrict our discussion to those studies done in the Western world Essentially, evidence on the epidemiology of waterborne disease in the West comes from two sources, reports of waterborne disease and prospective studies of sporadic disease

3.2 REPORTED OUTBREAKS

OF WATERBORNE DISEASE

Very few countries have satisfactory surveillance systems for waterborne disease Only the U.S and U.K have established surveillance systems with regular publica-tion of details on waterborne outbreaks In the U.S., the Center for Disease Control (CDC) has been collating and reporting on waterborne disease since 1971 In the U.K., the Public Health Laboratory Service Communicable Disease Surveillance Centre (CDSC) has been publishing biannual reports since 1994 Although data from both countries has been collected since before these schemes were implemented, data collection was less systematic The two systems differ from each other, each having its own strengths and weakness The U.S system is probably more compre-hensive including chemical incidents and many outbreaks of unknown aetiology American citizens appear more likely to contact their health departments should they suffer from a gastrointestinal illness By contrast, in the U.K system, which is based on reporting of laboratory isolations, cases are usually only identified after

with suppurative skin lesions

gastric cancer

Hepatitis E virus

2–4 weeks 6–8 weeks

Mild flu-like symtoms to severe fulminating hepatitis and death; death is especially common with Hepatitis E in pregnant women

Rotavirus

progress to asceptic meningitis, encephalitis, and paralysis

Echoviruses Enteroviruses

pneumonitis, and myalgia

TABLE 3.2 (continued)

Microbial and Parasitic Disease Linked to Drinking Water Consumption

Usual Incubation

Trang 5

they have been attended by doctors and samples have been taken for analysis On the other hand, once a patient attends a medical practitioner, a sample is more likely

to be sent for examination and once positive, reported to the surveillance systems In any event, waterborne outbreaks are probably significantly underreported in both countries

Reports of waterborne outbreaks in England and Wales are presented in

to private supplies In the U.K data, it is clear that there has been a significant change in the identified causes of waterborne disease during this century Up until

1970, waterborne disease was dominated by typhoid or paratyphoid Dysentery was

TABLE 3.3

Waterborne Outbreaks Associated with Public Water Supplies in England and Wales 1911–1998, Number of Outbreaks

in 10-Year Periods

10-Year

Period

Number of Outbreaks

Number of Cases and Deaths

Disease: Number of Outbreaks, Cases, and Deaths Site of Contamination

Source Distribution

0

0 Cryptosporidiosis: 10, 857+, 0

0

Cryptosporidiosis: 22, 2550+, 0

Source: Adapted from Galbraith 11 with additional data from Stanwell-Smith, 12 Furtado et al., 13

Trang 6

the only other infection of note during this period Since the 1970s, reports of waterborne outbreaks have increased substantially, although this increase has been

Campylo-bacter being described in the late 1970s and Cryptosporidium in the early 1980s The decline in the reporting of typhoid, a disease with a high mortality without adequate treatment, reflects improved water treatment and the disappearance of the pathogen from the general population The increase in the new pathogens reflects

compared to private water supplies reflects this pathogen’s sensitivity to disinfection

In the U.K., virtually all public supplies have some form of disinfection, usually

prev-alence in public supplies Although there are much fewer outbreaks reported from private supplies, a very small proportion of the population of England and Wales have a private supply Also, given their smaller size, private supply outbreaks are probably more likely to be missed Consequently, the relative risk of being involved

in a waterborne outbreak is probably much higher in people drinking private water

same trend over the century, as does the U.K data Over the years, typhoid declines

in importance from its once preeminent position There are, however, some major

TABLE 3.4

Waterborne Disease from Private Supplies in England and Wales

from 1941–1998 and Various Communicable Disease Reports

10-Year

Period

Number of Outbreaks

Number of Cases and Deaths

Disease: Number of Outbreaks, Cases, and Deaths

0 Campylobacter: 3, 520, 0

0 Campylobacter: 6, 147, 0

Giardia: 1, 31, 0

Cryptosporidiosis: 2, 66, 0

E coli: 1, 14, 0

Source: Adapted from Galbraith et al., 11 Stanwell-Smith, 12 and Furtado et al 13

Trang 7

TABLE 3.5

Aetiology of Waterborne Outbreaks in the U.S., 1920–1996

continued

Trang 8

differences between the U.S and U.K data The first thing to note is the much larger number of outbreaks in the U.S., even accounting for the larger population In part this is owing to the American detection of outbreaks where no pathogen was isolated, but it also probably relates to the different nature of the water supply industry in the U.S There are many more isolated small communities with their own water supplies in the U.S than in the U.K Many of these smaller supplies get little or no

to the U.K., although we suspect part of the explanation relates to the reported

One advantage of the U.S presentation is a more detailed analysis of the treatment

majority of non-community waterborne outbreaks were owing to untreated or inad-equately chlorinated groundwater For the larger community outbreaks, the causes of failure were more diverse, including inadequate disinfection of surface water, distri-bution deficiencies, groundwater problems, and filtration deficiencies

E coli O157 1 243

E coli 0157 2 35

Source: Adapted from Craun 14 with additional data from Moore et al., 15 Kramer et al., 16

and Levy 17

TABLE 3.5 (continued)

Aetiology of Waterborne Outbreaks in the U.S., 1920–1996

Trang 9

Although outbreaks are useful in identifying the microbiological and engineering

causes of waterborne disease, they cannot give an accurate estimate of the burden

of waterborne disease in a community Many outbreaks will go undetected To gain

an insight into overall disease burden, we have to turn to other epidemiological

methods In the next section we will consider some of the epidemiological studies

which have investigated the relationship between disease and water consumption

3.3 EPIDEMIOLOGICAL STUDIES

OF WATERBORNE DISEASE

There is very comprehensive literature on the effects of drinking water quality on

health Unfortunately, for this review, the vast majority concerns studies undertaken

world There are essentially two approaches The first approach is to conduct

case-control studies on diagnosed sporadic infection Clearly, this approach reveals

infor-mation on just a small proportion of infections, those owing to the specific disease

under investigation Consequently, we have to rely on prospective studies of illness

rates, either in cohort studies or experimental studies

Of the prospective cohort studies of drinking water and ill health, in our view,

the work of a group of French researchers is preeminent Their first work was a

collected data on water quality for each village and recorded the number of patients

who were diagnosed with gastroenteritis each week by their physician All villages

were supplied with untreated surface water Those villages whose water did not meet

to 1.36, 95% CI 1.24 to 1.49) The most predictive marker of illness was faecal

streptococci, although faecal coliforms were also independently associated By contrast,

total coliforms and aerobic plate counts were not independently associated with risk

TABLE 3.6

Causes of Waterborne Outbreaks, U.S., 1981–1990

Source: Reprinted from Craun 14

Trang 10

In a subsequent study, the group looked at the effect on health of chlorination

study, they recorded the rate of diarrhoea in some 2033 school children living in

24 French villages In these 24 villages, 13 did not give their water any treatment

as it already met statutory standards The other villages chlorinated their water but

did no other treatment Those children living in the villages with initially substandard

water were 1.4 times more likely to suffer from a diarrhoeal illness (95% CI 1.30 to

1.50) Interestingly, this excess risk was associated with the occurrence of small

epidemics Thus faecally polluted water continued to pose an excess risk even after

chlorination

An interesting approach to the issue of trying to quantify risk to health from

water was developed by two groups who looked at the temporal correlation between

first group looked at historical data correlated over time from January 1992 to April

1993 from Milwaukee County, WI (better known as the place where the world’s

in turbidity of 0.5 NTU was associated with a 2.35 (95% CI 1.34 to 4.12) increase

risk of gastroenteritis in children and 1.17 (0.91 to 1.52) in adults The second group

looked at the relationship between emergency visits and admissions to the Children’s

Hospital in Philadelphia for gastrointestinal illness The authors reported that an

interquartile increase in drinking water turbidity was associated with a 9.9% (2.9 to

17.3%) increase in visits in children, aged 3 years and over, 4 days later, a 5.9%

(0.2 to 12%) increase 10 days later in children 2 years and younger Hospital

admis-sions followed the same trend

point-of-use reverse-osmosis filters to one half of a study population in Montreal

Volun-teers kept a health diary and the researchers were able to compare self-reported

episodes of gastroenteritis in the two groups Throughout the study period, rates of

gastroenteritis were significantly higher in the group drinking unfiltered tap water,

although laboratory investigations were unable to identify any pathogen responsible

for this excess The authors estimated that about 30% of all cases of gastrointestinal

infections were attributable to the drinking water

In a subsequent experimental study, Payment and colleagues compared randomly

allocated volunteers to one of four study arms: tap water, tap water from a continuously

study was much less convincing than the previous one, although the authors still felt

able to suggest that 14 to 40% of gastrointestinal illnesses were related to drinking

water However, a major problem with Payment’s studies were that all his volunteers

knew which arm of the study they were in and thus the outcome of both his studies

could have been affected by reporting bias on the part of his volunteers At the time of

publication, variations of Payment’s studies were being repeated with the study design,

ensuring that volunteers would be unaware of whether they were drinking filtered or

unfiltered water These studies should be reported during the year 2000 or 2001

All the epidemiological studies reported previously have reported evidence for

the association between drinking water and gastrointestinal illness It would appear

that even the drinking water meeting current microbiological standards might be

Định dạng
Số trang	12
Dung lượng	809,82 KB