Professor POU/POE: Foodborne & waterborne disease

June 2, 2016

Considering the diversity of foods and water and their handling, it should not be a surprise that foodborne and waterborne disease risks are substantial.

Q: What is the extent of the microbial foodborne and waterborne disease risks in the U.S., and how do they compare?

A: Comprehensive and detailed statistics are non-existent, but estimates place food at a significantly higher risk than public drinking water.

We all consume food and water daily, but inherent risks are associated with anything that we ingest. Considering the diversity of foods and water and their handling, it should not be a surprise that foodborne and waterborne disease risks are substantial. We are constantly exposed to microorganisms in our living environment. Fortunately, most microorganisms are beneficial and not pathogens. Most food- and waterborne diseases in the U.S. are now not serious or fatal for healthy people, but exceptions exist. Foodborne diseases are being reported with greater frequency, which might or might not mean that they are increasing but they are certainly being identified more often. Although projected waterborne disease incidence is probably greater than we can measure, recognized waterborne disease outbreaks occur with very low and declining frequencies.

Many microorganisms cannot survive human stomach acidity, the gastrointestinal tract environment and the immune system, but many others can. The role of public health authorities is to work with producers, distributors and sellers to minimize the exposure risks to a feasible extent and reduce the numbers of serious disease incidences and deaths that can result from exposure to contaminated food and water. Additional risks exist in the home from plumbing and from food storage and preparation. Public water supplies are regulated and usually safe, but private wells are not usually tested or treated. We have a huge infrastructure and high number of requirements to ensure safety in water and food production, but they are not perfect.

Food risks & safety

Many opportunities exist for bacterial, viral or protozoan microbial contamination of food, from seed to plant or animal, to processing, distribution, home storage and preparation, cooking, and plate. Estimating the actual number of cases of foodborne disease, commonly called food poisoning, is very difficult, partly because many are subtle, including brief upset stomach, diarrhea and self-limiting unreported gastrointestinal illnesses where medical treatment is not sought. The Centers for Disease Control (CDC) estimates that each year about one in six (more than 48 million people) will become ill, 128,000 will be hospitalized, and 3,000 will die by consuming pathogen-contaminated food or beverages.

More than 250 potential foodborne diseases have been identified. The top five microorganisms accounting for many foodborne illnesses and rounded estimated cases are Norovirus (5.5 million), Salmonella nontyphoidal (1 million), Clostridium perfringens (1 million), Campylobacter (850,000) and Staphylococcus aureus (250,000). The top five foodborne illness pathogens resulting in hospitalization were Salmonella nontyphoidal (19,336); Norovirus (14,663); Campylobacter (8,463); Toxoplasma gondii, a parasite (4,428); and E.coli O157H7 (2,138). The top five foodborne pathogens resulting in deaths were Salmonella nontyphoidal (378), Toxoplasma gondii (327), Listeria mocytogenes (255), Norovirus (149) and Campylobacter (76).

Salmonella bacteria are widespread in animals and can spread to humans from foods of animal origin. Salmonellosis symptoms include fever, diarrhea and abdominal cramps. Norovirus causes gastrointestinal illness with vomiting and usually resolves within three days. Infections are readily transmitted by human contact, and food contamination by food service workers is not uncommon. Campylobacter is the most commonly identified worldwide cause of diarrheal illness. It is common in poultry and spread by the ingestion of undercooked chicken. Clostridium perfringens is widespread in the environment, can be present on raw meat and produces a toxin that causes illness. In addition to direct infections, several pathogens, such as Staphylococcus aureus and Clostridium botulinum, produce toxins that survive after the infection. The CDC estimates that up to 60 million people in the U.S. may be infected with Toxoplasma gondii without symptoms because healthy immune systems can suppress it. Handling contaminated animal products and even exposure to cat feces can be a risk, especially to pregnant women.

Changing foodborne disease causes

Typhoid fever, tuberculosis and cholera were once common foodborne illnesses. Pasteurization of milk, better canning practices and process water disinfection have virtually eliminated those diseases in developed countries. More recently foodborne cases of cyclosporiasis have been caused by the contamination of Guatemalan raspberries; Vibrio parahemolyticus, caused infections from eating raw oysters from Galveston Bay, Texas; cryptosporidiosis from unpasteurized apple cider probably caused by apples collected from the ground where they could contact animal feces; and kidney failure from hemolytic anemia caused by E. coli O157H7, sometimes from consuming inadequately cooked hamburger meat. Some of these outbreaks have been the result of imported foods that had not been produced under proper sanitary conditions.

Detecting foodborne diseases

Most foodborne diseases in the population are undiagnosed unless they are serious enough to require physician care or hospitalization. Even then, the specific microorganism may not be identified because many diseases, such as from norovirus, are not reportable. The disease surveillance process involves the collection of incidence data at the county health department level, reporting to the state, which reports to the CDC, but not all states participate in the system and reportable diseases are not identical in each state. CDC’s FoodNet surveillance system is a collaborative program among the CDC, 10 state health departments, the U.S. Department of Agriculture Food Safety and Inspection Service, and the Food and Drug Administration. It conducts surveillance for several diseases and covers 15 percent of the U.S. population. Each year it identifies more than 1,000 foodborne outbreaks that are investigated by local and state health departments.

Foods associated with foodborne illness

The CDC lists the following foods that have a higher potential of contamination:

  • Raw meat, raw eggs and unpasteurized milk
  • Filter-feeding shellfish, such as oysters
  • Foods produced by combining numerous animal sources, such as bulk raw milk, raw eggs or hamburger meat
  • Fruits and vegetables consumed raw
  • Unpasteurized fruit juice

Preventing foodborne disease

Some suggestions for reducing foodborne disease risks are:

  • To assure that producers and shippers meet U.S. standards, improve and implement more comprehensive controls and inspections on imported fresh and processed foods.
  • Take special care to know the source and handling when consuming any raw foods, especially oysters.
  • Do not consume unpasteurized milk and eggs without cooking them.
  • Wash lettuce, fruits and vegetables well if they will be consumed raw. However, even chlorinated water washes have limited effectiveness because of the surface properties of many foods.
  • Do not mingle external fruit surfaces with the fruit or juice. Whole fruit or vegetable smoothies can be questionable.
  • Practice good food sanitation in the home. Wash hands frequently when cooking. Do not mix raw and cooked food on cutting boards or plates. Clean utensils and sanitize kitchen surfaces. Cook foods, especially meats, to the recommended temperatures.
  • Do not store foods under inappropriate temperature and moisture conditions or for excessive times.
  • Be careful with picnic foods, especially those containing eggs and mayonnaise, that are susceptible to spoilage at warmer temperatures.
  • Taste and smell are good sensors. If it does not seem right, do not eat it.

Waterborne disease risks

The CDC has estimated from published projections that from 4 to 32 million annual cases of acute gastrointestinal illness may occur from the approximately 150,000 public drinking water supplies in the U.S. Most of the estimates fall in between or toward the lower end. The large uncertainties are because of the similar circumstances of self-limiting and untreated mild cases and the limited reporting described for foodborne disease detection. However, most of the waterborne numbers are significantly smaller than the foodborne numbers, which is quite reasonable. Public water supplies of 25 persons or more that provide piped water consumed regularly by most people are subject to significant regulatory controls including monitoring, treatment requirements and finished water quality requirements. Boil water notices are issued to advise the public during a risk situation.

Historically, 1,870 outbreaks were reported in all water types from 1920 to 2002, ranging from 11.1 to 32.4 per year, and averaging 10,648 cases and 14 deaths per year, including both chemical and microbial causes. However, these numbers were limited by the capabilities of the surveillance systems in place and would have been much higher since legionellosis was not reportable before 2001. As a result most outbreaks were probably not detected.

Since the passage (1974) and significant implementation (1980) of the Safe Drinking Water Act, water management and compliance with regulations have significantly improved and reported waterborne disease outbreaks have been in a declining trend. One exception was Milwaukee’s cryptosporidiosis outbreak of 1993 because of an unusual systemic problem, the cause of which was corrected, while surveillance and detection have improved. The types and causes of waterborne diseases have also changed, from those associated with inadequate water treatment, to those associated with distribution system problems, especially microbial regrowth in plumbing biofilms.

The more relevant and most up-to-date outbreak information from the last two CDC Morbidity and Mortality Weekly Reports cover 2009 to 2010 and 2011 to 2012. The 2009 to 2010 report recorded 33 outbreaks, 1,040 cases, 83 hospitalizations and nine deaths. Legionella accounted for 58 percent of the outbreaks (19), 7 percent of the illnesses (72) and all nine deaths. Campylobacter accounted for 12 percent of the outbreaks and 78 percent of illnesses. Giardia, norovirus, E. coli and cryptosporidium contributed a smaller number of outbreaks and illnesses.

In the 2011 to 2012 period, reports recorded 32 outbreaks, 431 cases of illness, 102 hospitalizations and 14 deaths. Legionella accounted for 66 percent of the outbreaks, 26 percent of the illnesses and all 14 deaths. Noroviruses were responsible for 32  percent of cases, and non-legionella bacteria caused 21 percent of the cases (90), including Shigellla sonnai, E. coli and Pantoea agglomerans. The latter was unusual and caused hospital-acquired blood infections, probably from using drinking water to produce infusion fluids. The microorganism was identified in the drinking water, an ice machine and sinks. Interestingly, no illnesses from cryptosporidium were reported, and only one Campylobacter and two norovirus outbreaks were identified in the 2011 to 2102 period.

Most of the reported cases and outbreaks for both periods were associated with drinking water plumbing systems (legionellosis), and the next most reported were associated with untreated groundwaters.


Food contamination somewhere in the production-to-consumption sequence appears to be a significantly greater health risk than public drinking water supplies, but drinking water is an important contributor to risks from ingestion or inhalation exposures, especially  legionellosis. Room for improvement exists in the prevention and risk reduction in both media. Some improvement would occur from having stricter control over the safety of imported foods and better storage, sanitation and preparation practices in homes. Swab tests usually find more microorganisms in kitchens than bathrooms.

Drinking water quality and safety have improved, but risks are still associated with microbial regrowth in plumbing and the consumption of untreated water from both public and private water sources. Point of use technologies can further reduce drinking water risks if they are properly selected and managed.

Dr. Joe Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants and technical editor of Water Technology. He is a former director of the EPA Drinking Water Standards Division.

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