Enteric Diseases Transmitted Through Food, Water, and Zoonotic Exposures

Foodborne Disease

The Centers for Disease Control and Prevention (CDC) estimates that 48 million domestically acquired foodborne illnesses occur in the US each year, resulting in approximately 128,000 hospitalizations and 3000 deaths. ^, Among known pathogens, norovirus is estimated to be the leading cause of foodborne illness in the United States, followed by nontyphoidal Salmonella , Clostridium perfringens , and Campylobacter . The highest incidence rates for nontyphoidal Salmonella , Campylobacter , Shigella , Escherichia coli O157, and Yersinia enterocolitica occur in children aged <5 years, and the highest rate of invasive Cronobacter spp. (formerly Enterobacter sakazakii ) infections is among infants. ^, These 6 bacterial pathogens are estimated to cause >290,000 illnesses annually among children aged <5 years and to result in nearly 8000 hospitalizations and 64 deaths. ^, Nontyphoidal Salmonella is estimated to cause the most hospitalizations and deaths each year in this age group. Although norovirus causes approximately 50% of recognized foodborne illnesses associated with outbreaks in the US, the highest rates of hospitalizations and deaths associated with norovirus occur in adults aged ≥65 years.

Most foodborne illnesses are not linked to outbreaks. However, data from foodborne illness outbreaks provide useful insights into important pathogens, new and high-risk food vehicles, and settings associated with illness. From 2009–2017, >7,400 foodborne disease outbreaks were reported to the CDC, resulting in approximately 130,000 illnesses, 7,400 hospitalizations, and 180 deaths. Norovirus continues to be the leading cause of confirmed, single-agent foodborne disease outbreaks in the US, followed by Salmonella species.

Many different foods have been linked to foodborne illness outbreaks ( Table 58.1 ). During 2009–2017, the food categories most commonly implicated in foodborne outbreaks in the US were fish, dairy, and chicken. Contaminated produce increasingly has been linked to foodborne outbreaks caused by norovirus, Salmonella , E. coli O157:H7, and other Shiga toxin-producing E. coli (STEC), Listeria monocytogenes , Shigella spp., Cryptosporidium , and Cyclospora cayetanensis . Leafy green vegetables (e.g., lettuce) were linked to recent STEC, Salmonella , and Listeria outbreaks. Imported fresh raspberries, basil, cilantro, and snow peas have been linked to outbreaks of Cyclospora infection. ^{, ,} Frozen berries have been linked to outbreaks of hepatitis A and norovirus.

Despite health risks, unpasteurized (raw) milk continues to be sold legally in many states and sometimes is given to school groups that visit farms; more than 200 outbreaks linked to unpasteurized milk or cheese have been reported in the United States since 1993, and etiologic agents include norovirus, Salmonella, Campylobacter , Listeria monocytogenes , STEC, and Cryptosporidium . ^, During 2007–2012, most outbreaks associated with unpasteurized milk were caused by Campylobacter spp. Formula-fed infants have a heightened risk of salmonellosis compared with breastfed infants, perhaps because they are not receiving immunologic protection from human milk or because of contamination of formula during preparation or feeding. ^, Powdered infant formula is also associated with Cronobacter spp. (formerly Enterobacter sakazakii ) infection in infants, which can result in sepsis and meningitis.

Commercial processed foods and ready-to-eat foods also have been implicated in outbreaks of Salmonella , E. coli O157, and L. monocytogenes infections, including prepackaged cookie dough, salami made with contaminated pepper, soynut butter, and ice cream. Ready-to-eat foods, such as salads and sandwiches, and self-service food items, are often implicated in norovirus and shigellosis outbreaks.

Toxin-produced enteric illnesses caused by C. perfringens , Bacillus cereus , and S. aureus are estimated to cause 1.3 million illnesses annually in the US. Illness outbreaks caused by these agents are most commonly linked to errors in food handling, such as holding foods at room or outdoor temperatures for several hours, improper reheating practices, and slow cooling of foods. C. perfringens spores are ubiquitous in the environment; illness occurs after ingestion of contaminated food with resulting sporulation and toxin production in the gastrointestinal tract. Meat and poultry are most commonly implicated in C. perfringens outbreaks. ^, B. cereus has been isolated from a wide variety of foods, including rice, spices, dried foods, vegetables, and dairy products. ^, Outbreaks of the short-incubation emetic syndrome of B. cereus food poisoning most commonly are associated with rice, particularly fried rice. Outbreaks of longer-incubation diarrheal syndrome have been linked to a variety of foods, including vegetables, milk products, sauces, and pudding, in addition to meat products. ^, Staphylococcal food poisoning has been linked to many different food types, including cooked meats and poultry, custard or cream-filled baked goods, dairy products, sandwiches, and salads. ^,

Foodborne botulism is caused by ingestion of foods contaminated with preformed botulinum toxin. In the US, foodborne botulism is typically associated with consumption of home-canned, low-acid foods, such as vegetables and fish. ^, However, commercially produced products such as carrot juice and canned chili have been linked to past outbreaks. ^, Infant botulism occurs after swallowed spores of Clostridium botulinum (and rarely, other neurotoxigenic Clostridium spp . ) germinate, temporarily colonize the large intestine, and produce botulinum toxin. Honey has been implicated as the source of C. botulinum spores in some cases of infant botulism, but recommendations to avoid feeding honey to infants has made it an uncommon source.

Scombroid fish poisoning is caused by consuming fish with elevated histamine levels resulting from improper storage. Fish in the Scombridae family (e.g., mackerel, tuna, skipjack) are most commonly associated with scombroid fish poisoning. Ciguatera fish poisoning is caused by toxins that originate in the benthic marine micro-organism Gambierdiscus toxicus and accumulate in fish flesh, particularly in large predatory reef fish. Ciguatera fish poisoning has been associated with more than 400 species of fish (including barracuda, snapper, and amberjack), and with fish of varying sizes. Shellfish poisonings are associated with consuming shellfish contaminated with algal toxins. The occurrence of specific shellfish poisonings varies with geographic area, the presence of toxin-producing algae and associated toxins, and the success of monitoring programs designed to prevent harvesting contaminated shellfish.

Shellfish, especially bivalve mollusks, are important vehicles of foodborne illness, particularly because they are often consumed raw. Shellfish can be colonized naturally with pathogenic Vibrio organisms, including Vibrio vulnificus , Vibrio cholerae non-O1, Vibrio parahaemolyticus , and Vibrio mimicus . As filter feeders, shellfish concentrate pathogens from contaminated water, including hepatitis A virus, norovirus, toxigenic V. cholerae O1, Shigella , and Plesiomonas .

Foodborne outbreaks of unintentional toxic metal poisoning are most often associated with acidic beverages such as lemonade, fruit punch, and carbonated drinks that have been stored in corroded metallic containers. ^, Mushroom poisoning occurs most often in the spring, late summer, and fall and is associated with species-specific syndromes. ^,

Waterborne Disease

Enteric waterborne disease resembles disease resulting from contamination of food and can be caused by many of the same pathogens (see Table 58.1 ). Large waterborne disease outbreaks resulting in enteric illness have been caused by Cryptosporidium , Giardia , Campylobacter , E. coli , Salmonella , Shigella , chemical agents, hepatitis A virus, norovirus, and other agents. Cryptosporidium , a chlorine-tolerant protozoan parasite, was linked to 21 drinking-water outbreaks from between 1971–2017; a single outbreak in Milwaukee in 1993 accounted for an estimated 403,000 cases. ^{, , ,}

Because water, with the exception of bottled water, is normally not a widely distributed product, most detected waterborne disease outbreaks are confined geographically to the water distribution service area, and multistate outbreaks are rare. An estimated 16.4 million cases of acute gastroenteritis are associated with public drinking water systems annually. However, the annual number of reported drinking water–associated outbreaks in the US is substantially lower than during the 1970s to early 1980s, particularly outbreaks associated with public water systems. ^, This change corresponds with the implementation of federal regulations designed to reduce illnesses associated with public water systems. Privately owned systems that serve fewer than 25 people do not fall under the drinking water regulations established by the US Environmental Protection Agency (EPA) to protect water quality in public drinking water systems. Although it is more difficult to identify illness outbreaks associated with small systems, increased illnesses among children have been associated with the use of water from private wells. Water system contamination resulting in drinking water–associated outbreaks can occur at a variety of points, including the water source, treatment processing, storage, distribution system, premise plumbing, and point of use. In studies of public systems using groundwater, human enteric viruses, such as enteroviruses and norovirus, have been isolated from aquifers that may have been contaminated from surface water intrusion or sewage discharges. ^, The broader public health impact of such contaminated groundwater could be substantial because approximately half of the US population relies on groundwater for domestic use, either through public or individual water systems.

In contrast, the number of enteric disease outbreaks associated with recreational water has increased over the past decades. ^, These illnesses are caused by pathogens transmitted by ingesting, inhaling aerosols, or having contact with contaminated water in pools, hot tubs, interactive fountains, lakes, rivers, oceans, and so forth. Illnesses also can be caused by chemicals in the water or by chemicals that volatilize from the water and cause indoor air quality problems.

Water used for recreational purposes may be treated or untreated. Cryptosporidium has become the leading cause of enteric illness outbreaks associated with treated recreational water (e.g., swimming pools and interactive fountains), accounting for >80% of the these outbreaks reported to CDC during 2005–2014. Because Cryptosporidium is extremely tolerant to chlorine levels used in treated water, these outbreaks can occur even in well-maintained facilities and have the potential to expand community wide, starting with recreational water transmission and moving by person-to-person transmission into childcare programs and other settings. Outbreaks of gastrointestinal illness associated with untreated water primarily are caused by bacteria and viruses (e.g., E. coli , norovirus, Shigella ) and usually are linked to swimming in lakes or ponds. Swimmers can be important sources of water contamination.