Epidemiology of Drinking Waterborne
and Foodborne Disease
ENVR 133 - Lecture 8
Mark D. Sobsey
Pyramid of Water- and Food-borne Disease
Drinking Water-borne Disease Outbreaks in the U.S.
• Information comes from reported waterborne outbreaks
• Based on two or more cases from a drinking water
• Data compiled by a passive reporting system to the Centers for
Disease Control (CDC), and the Environmental Protection Agency
(EPA) for water
• Many outbreaks are not noticed or reported
– Reported outbreaks are the "tip of the iceberg”
– Estimated unreported/unrecognized outbreaks: 50-90%
• Etiological agent is not identified or recognized in many outbreaks
– The fraction of outbreaks for which an etiological agent is
identified had increased in recent years
– Etiologic agent is rarely isolated from the incriminated water
– Etiologic agent is usually isolated and identified from cases of
ill persons
Waterborne Outbreaks in the United States, 1989-1994
Etiologic Agent
No. Outbreaks
Acute GI (unknown)
44
Cryptosporidium parvum
8
Giardia lamblia
16
Hepatitis A virus
4
Norwalk-like viruses
1
E. coli O157:H7
1
Cyclospora cayatenensis
1
Shigella spp.
7
Salmonella sp.
1
Vibrio cholerae (non-01) 1
Chemicals:
Pb, NO3, F and Cu
13
No. Cases
16,264
406,822
1,205
81
900
243
21
570
625
11
TOTAL
427,256
87
394
WB Disease Outbreaks 2001-2002
• 31 drinking water OBs reported by
19 states.
• 1,020 ill persons and seven
deaths.
• Microbe or chemical causing OB
was identified for 24 (77.4%) of
the 31 outbreaks.
• Of the 24 identified outbreaks,:
• 19 (79.2%) were associated with
pathogens
• 5 (20.8%) associated with acute
chemical poisonings.
WB Disease Outbreaks 2001-2002
•
•
•
•
•
5 OBs caused by norovirus
5 OBs by parasites
3 OBs by non-Legionella bacteria
6 OBs of Legionnaires disease (LD)
7 OBs of acute GI illness of unknown etiology
suspected of having an infectious cause.
• Of the 25 non-Legionella Obs:
• 23 (92.0%) in systems using groundwater sources
• 9 (39.1%) of these 23 GW ObB were associated with
private noncommunity wells not regulated by EPA
Preventing Drinking Waterborne Outbreaks
• For surface water supplies, most outbreaks could be
eliminated if treatment consisted of proper filtration
(including pre-treatment by coagulation-flocculation)
and disinfection.
• For groundwater supplies, most outbreaks could be
eliminated if proper disinfection was used.
Actual Risk of Enteric Illness in a Drinking Water Supply
from a Surface Source: Epidemiological Studies
•
•
•
•
•
Payment et al., 1991, 1997
Laval (Montreal suburb), Quebec, Canada
Drinking water from a sewage-contaminated river source
Water is extensively treated to make drinking water
Compared GI illness rates in two sets (~300 each) of households
(four sets in 2nd study):
– One set used ordinary tap water
– Other set used reverse osmosis filtered water (no pathogens)
• 2nd study: also distribution system-tapwater
• 2nd study: also treated water bottled at water treatment plant
– GI illness rates were about 25-35% (~15% in 2nd study) higher in tap
water households
– Dose-response relationship: increased illness with increased tap
water consumption (glasses/day)
– No pathogens were detected in the water
– Water met all standards for quality, including coliforms and turbidity.
“Payment Studies”: References
• Payment P., et al, (1991). A Randomized Trial to Evaluate the Risk
of Gastrointestinal Disease due to Consumption of Drinking Water
Meeting Current Microbiological Standards. American Journal of
Public Health 81 (6) 703-708.
• Payment P., et al (1997). A prospective epidemiological study of
gastrointestinal health effects due to the consumption of drinking
water. International Journal of Environmental Health Research.
7(1). 1997. 5-31
“Payment Study”, 1991:
Risks of Gastrointestinal Illness from Tapwater vs. RO-filtered Water
Percent of Study Subjects Reporting HCGI Symptoms and Mean Number of
Episodes per Unit of Observation in Both Periods Combined
Group
Filtered Water (n=272)
Tap Water (n=262)
Unit of
% with
Mean Number
% with
Mean Number
Observation
Episodes of Episodesa
Episodes of Episodes
Familey
62.0
3.82
67.7
4.81
Informant
20.0
1.70
23.1
2.10
Youngest child 42.3
1.83
46.3
2.37
aDerived by logistic regression with covariables age, sex, geographic subregion. Only subjects who had complete data sets in both periods are
included in this table.
bMean number of episodes among those subjects who reported at least one
episode.
“Payment Study”, 1991:
Risks of Gastrointestinal Illness from Tapwater vs. RO-filtered Water
Incidence of HCGI Episodes Derived from Poisson Regression Analysis, by Study
Group for Each of Three Units of Observationa
Group
Period 1
Period 2
Unit of
Filtered
Tap
Preventable Filtered
Tap
Preventable
Observation (n=296)
(n=304)
Fraction (%) (n=262)
(n=276) Fraction (%)
Family
0.65
1.00**
36.0
0.43
0.64**
32.8
Informant
0.64
1.00*
36.0
0.44
0.63*
30.2
Youngest
0.88
1.24*
30.7
0.56
0.80*
30.0
child
aAnnual incidence per unit of observation, derived by Poisson regression with age, sex,
and subregion in the models.
*Difference between the incidence rates is significant at p<0.05
**Difference between the incidence rates is significant at p<0.01
Foodborne Disease in The USA: 1993-1997
• Bacterial pathogens caused most outbreaks/infections with
a known etiology
• But, 68% of reported FBDOs were of unknown etiology
– Need improved epidemiologic and lab investigations.
– ~ 50% had incubations period of >15 hours, suggesting
viral etiology. Viruses (e.g., Norwalk-like viruses) are likey
a much more important cause of foodborne disease
outbreaks than is currently recognized.
– Local and state public health lack resources and expertise
to diagnose viral pathogens, but the methods are now
increasingly available in some state laboratories.
– Viral outbreaks are more likely to detected in the future.
Foodborne Disease in the Home
• About half of all Salmonella cases result from
unsafe handling of food in the home.
• Foodborne illness costs the United States $23
billion annually.
• Foodborne illness is often mistaken for “the flu,
as many of the symptomsa are similar:
– stomach pain, diarrhea, nausea, chills, fever, and
headache.
• Many experts believe the kitchen is home to
more potentially dangerous bacteria than even
the bathroom.
Foodborne Disease in The USA: 1993-1997
FBDOs with a known etiology:
• multistate outbreaks caused by contaminated produce and
outbreaks caused by E. coli O157:H7 remained prominent.
• S. enteritidis remains a major cause of illness and death.
– ~40% of persons who died from S. enteritidis were residents
of nursing homes.
– Seriousness of S. enteritidis in elderly persons, many of
whom might be immunocompromised.
– Decrease risks for egg-associated infections of S. enteritidis
by not eating raw or undercooked eggs.
– Nursing homes, hospitals, and commercial kitchens should
use pasteurized egg products for all recipes requiring pooled
or lightly cooked eggs. Proper egg storage in homes.
• Several outbreaks involved imported food items, emphasizes the
role of food production and distribution in FBDOs.
Foodborne Disease Burden in the Unites States
• Estimated 76 million illnesses and 5,000
deaths each year.
• Foodborne diseases are common, but only a
fraction of these illnesses are routinely
reported to CDC
– Passive surveillance system
– Many diseases not reportable
– a complex chain of events must occur to report a
foodborne infection to CDC
– Most household foodborne infection are not
recognized or reported
Salmonella Infection
• Causes an estimated 1.4 million foodborne
illnesses/year
• From 1993-1997, only 189,304 Salmonella inections
(~38,00/year) reported through the National
Salmonella Surveillance System
– a passive, laboratory-based system.
• In the same period, 357 recognized outbreaks of
Salmonella infection resulting in 32,610 illnesses
were reported through the Foodborne-Disease
Outbreak Surveillance System.
• These system greatly underestimate the burden of
foodborne disease.
Active Surveillance Network for Foodborne
Disease in the United States: FoodNet
• Foodborne disease component of the CDC's Emerging
Infections Program (EIP).
• Established in 1995
• Collaborative project among CDC, several EIP sites (states
cities and territories), U.S. Department of Agriculture
(USDA), and the U.S. Food and Drug Administration (FDA).
• Consists of active surveillance for foodborne diseases and
• related epidemiologic studies designed to help public health
officials better understand the epidemiology of foodborne
diseases in the United States.
FoodNet Surveillance Sites
FoodNet Program
Tracks foodborne illness
using:
• surveys of physicians
and laboratories,
• case-control studies
• active case finding of
targeted pathogens
FoodNet Website:
http://www.cdc.gov/foodnet/default.htm
Targeted Pathogens:
Bacteria:
• Campylobacter
• E. coli O157
• Listeria
• Salmonella
• Shigella
• Vibrio
• Yersinia
Parasites:
• Cryptosporidium
• Cyclospora
Goals of FoodNet
• Describe the epidemiology of new and
emerging bacterial, parasitic, and viral
foodborne pathogens
• Estimate the frequency and severity of
foodborne diseases that occur.
• Determine how much foodborne illness
results from eating specific foods, such as
meat, poultry, eggs produce, etc.
Components of FoodNet
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•
•
•
•
Active laboratory-based surveillance
Survey of clinical laboratories
Survey of physicians
Survey of the population
Epidemiologic Studies
Water- and Foodborne Illness Surveillance
in Other Countries
• Efforts vary from country to country
• Most have little if any surveillance
• Some have more active and integrated
surveillance than in the United States
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–
–
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National health care systems
Integrated laboratories
Subsidized laboratory analyses
Other incentives
• political, social, etc.
Laboratory Reports of Gastrointestinal Infections in
England and Wales
Overview of Communicable Diseases
England and Wales - Priorities