Epidemiology of drinking waterborne and foodborne disease
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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

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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

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Waterborne Outbreaks in the United States, 1989-1994

Etiologic Agent No. Outbreaks No. Cases

Acute GI (unknown) 44 16,264

Cryptosporidium parvum 8 406,822

Giardia lamblia 16 1,205

Hepatitis A virus 4 81

Norwalk-like viruses 1 900

E. coli O157:H7 1 243

Cyclospora cayatenensis 1 21

Shigella spp. 7 570

Salmonella sp. 1 625

Vibrio cholerae (non-01) 1 11


Pb, NO3, F and Cu 13 394

TOTAL 87 427,256

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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.

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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

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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.

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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.

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“Payment Studies”: References from a Surface Source: Epidemiological Studies

  • 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

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“Payment Study”, 1991: from a Surface Source: Epidemiological Studies

Risks of Gastrointestinal Illness from Tapwater vs. RO-filtered Water

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“Payment Study”, 1991: from a Surface Source: Epidemiological Studies

Risks of Gastrointestinal Illness from Tapwater vs. RO-filtered Water

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Foodborne Disease in The USA: 1993-1997 from a Surface Source: Epidemiological Studies

  • 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.

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Foodborne Disease in the Home from a Surface Source: Epidemiological Studies

  • 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.

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Foodborne Disease in The USA: 1993-1997 from a Surface Source: Epidemiological Studies

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.

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Foodborne Disease Burden in the Unites States from a Surface Source: Epidemiological Studies

  • 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

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Salmonella Infection from a Surface Source: Epidemiological Studies

  • 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.

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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.

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FoodNet Surveillance Sites United States: FoodNet

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Tracks foodborne illness using: United States: FoodNet

surveys of physicians and laboratories,

case-control studies

active case finding of targeted pathogens

Targeted Pathogens:



E. coli O157









FoodNet Program

FoodNet Website:


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Goals of FoodNet United States: 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.

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Components of FoodNet United States: FoodNet

  • Active laboratory-based surveillance

  • Survey of clinical laboratories

  • Survey of physicians

  • Survey of the population

  • Epidemiologic Studies

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Water- and Foodborne Illness Surveillance in Other Countries United States: FoodNet

  • 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.

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Overview of Communicable Diseases and WalesEngland and Wales - Priorities