Epidemiology of Drinking Waterborne and Foodborne Disease

ENVR 421

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 No. CasesAcute GI (unknown) 44 16,264Cryptosporidium parvum 8 406,822Giardia lamblia 16 1,205Hepatitis A virus 4 81Norwalk-like viruses 1 900E. coli O157:H7 1 243Cyclospora cayatenensis 1 21Shigella spp. 7 570Salmonella sp. 1 625Vibrio cholerae (non-01) 1 11Chemicals:

Pb, NO3, F and Cu 13 394

TOTAL 87 427,256

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

Percent of Study Subjects Reporting HCGI Symptoms and Mean Number ofEpisodes per Unit of Observation in Both Periods Combined

GroupFiltered Water (n=272) Tap Water (n=262)

Unit ofObservation

% withEpisodes

Mean Numberof Episodesa

% withEpisodes

Mean Numberof Episodes

Familey 62.0 3.82 67.7 4.81Informant 20.0 1.70 23.1 2.10Youngest child 42.3 1.83 46.3 2.37aDerived by logistic regression with covariables age, sex, geographic sub-region. Only subjects who had complete data sets in both periods areincluded in this table.bMean number of episodes among those subjects who reported at least oneepisode.

“Payment Study”, 1991:Risks of Gastrointestinal Illness from Tapwater vs. RO-filtered Water

Incidence of HCGI Episodes Derived from Poisson Regression Analysis, by StudyGroup for Each of Three Units of Observationa

GroupPeriod 1 Period 2

Unit ofObservation

Filtered(n=296)

Tap(n=304)

PreventableFraction (%)

Filtered(n=262)

Tap(n=276)

PreventableFraction (%)

Family 0.65 1.00** 36.0 0.43 0.64** 32.8Informant 0.64 1.00* 36.0 0.44 0.63* 30.2Youngestchild

0.88 1.24* 30.7 0.56 0.80* 30.0

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

“Payment Study”, 1991:Risks of Gastrointestinal Illness from Tapwater vs. RO-filtered Water

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: 1993-1997FBDOs 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

Targeted Pathogens:

Bacteria:• Campylobacter • E. coli O157 • Listeria • Salmonella• Shigella • Vibrio • Yersinia

Parasites:• Cryptosporidium• Cyclospora

FoodNet Website:

http://www.cdc.gov/foodnet/default.htm

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

• 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– 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