Salmonella species cause diarrhea and systemic infections, which can be fatal in particularly susceptible persons, such as the immunocompromised, the very young and the elderly. Animals used for food production are common carriers of Salmonella, which can subsequently contaminate foods such as meat, dairy products and eggs. Foods often implicated in outbreaks include poultry and poultry products, meat and meat products, dairy products, egg products, seafood and fresh produce. An estimated 800,000 to four million infections occur every year in the U.S., most of them as individual cases apparently unrelated to outbreaks. Between 128,000 and 640,000 of those infections are associated with Salmonella enteritidis in eggs. Over the past decade, more than 500 outbreaks have been attributed to S. enteritidis, with more than 70 deaths. In 1994 an estimated 224,000 people became ill from consuming ice cream in one outbreak alone.
The bacterium Campylobacter is the most frequently identified cause of acute infectious diarrhea in developed countries and is the most commonly isolated bacterial intestinal pathogen in the U.S.. It has been estimated that between two and four million cases of campylobacteriosis occur every year with an associated 120 to 360 deaths. Campylobacter jejuni and C. coli (two closely related species) are commonly foodborne and are the infectious agents most frequently described in association with Guillain-Barr syndrome, as frequently as one in 1,000 cases. Several prospective studies have implicated raw or undercooked chicken as major sources of C. jejuni/coli infections. Unpasteurized milk and untreated water have also caused outbreaks of disease.
Toxin-producing Escherichia coli
Several strains of the bacterium E. coli cause a variety of diseases in humans and animals. E. coli O157:H7 is a type associated with a particularly severe form of human disease. E. coli O157:H7 causes hemorrhagic colitis, which begins with watery diarrhea and severe abdominal pain and rapidly progresses to passage of bloody stools. It has been associated with HUS, a life-threatening complication of hemorrhagic colitis characterized by acute kidney failure that is particularly serious in young children. E. coli O157:H7 is found in cattle, but there may be other reservoirs; the dynamics of E. coli O157:H7 in food-producing animals are not well understood. Approximately 25,000 cases of foodborne illness can be attributed to E. coli O157:H7 every year, with as many as 100 deaths resulting. E. coli O157:H7 outbreaks have recently been associated with ground beef, raw milk, lettuce, and minimally processed and fresh fruit juices. The most recent outbreak in the fall of 1996 in three western states and British Columbia was associated with unpasteurized apple juice and sickened 66 people, causing the death of one child.
Vibrio species are gram-negative bacteria most commonly associated with seafood-containing dishes. Vibrio parahaemolyticus is the species most commonly reported as a cause of foodborne disease; it generally causes watery diarrhea and abdominal pain lasting one to seven days and commonly follows consumption of improperly handled, cold seafood salads. V. vulnificus is one of the more serious foodborne pathogens, with a case fatality rate for invasive disease that exceeds 50 percent. Most cases of foodborne V. vulnificus infections occur in persons with underlying illnesses (particularly liver disorders) who eat raw mollusks. Since the late 1980s, the Food and Drug Administration, the Centers for Disease Control and Prevention, and the Gulf Coast states have intensified efforts to collect information on vibrio infections and on the microorganisms' ecology, to improve our ability to prevent foodborne infections.
T. gondii is a parasitic protozoan. Some 1.4 million cases of toxoplasmosis occur annually with an associated 310 deaths. Healthy adults who become infected usually have no symptoms but might get diarrhea. Pregnant women who become infected can pass the disease to their fetuses. In infants infected before birth, fatality is common. Should the infant survive, the effects of infection are typically severe (for instance, mental retardation). The disease can be life-threatening in persons with weakened immune systems and often is fatal to people with HIV/AIDS. T. gondii has been found in virtually all food animals. The two primary ways that humans become infected are consumption of raw or undercooked meat containing T. gondii or contact with cats that shed cysts in their feces during acute infection. Under some conditions, the consumption of unwashed fruits and vegetables can contribute to infections.
C. parvum is a parasitic protozoan. The most common consequence of infection in healthy people is profuse, watery diarrhea lasting up to several weeks. Children are particularly susceptible. Cryptosporidiosis can be life-threatening among people with weakened immune systems. The largest recorded outbreak of cryptosporidiosis was a waterborne outbreak in Milwaukee in 1993, affecting more than 400,000 people. More recently, a waterborne outbreak in Las Vegas resulted in at least 20 deaths. The first large outbreak of cryptosporidiosis from a contaminated food occurred in 1993; that outbreak was attributed to fresh-pressed apple cider. Cryptosporidium also is found in animal manures.
Norwalk viruses are important causes of sporadic and epidemic gastrointestinal disease that involve overwhelming, dehydrating diarrhea. An estimated 181,000 cases occur annually with no known associated deaths. In January 1995 a multistate outbreak of viral gastroenteritis caused by Norwalk virus was associated with the consumption of oysters. A 1993 Louisiana outbreak of Norwalk virus gastroenteritis involved 70 ill people and was associated with the consumption of raw oysters. In 1992 an outbreak resulted in 250 cases. Outbreaks of Norwalk virus intestinal disease have been linked to contaminated water and ice, salads, frosting, shellfish, and person-to-person contact, although the most common food source is shellfish. Several such outbreaks are believed to have been caused by oysters contaminated by sewage dumped overboard by oyster harvesters and recreational boaters.
Hepatitis A (HAV) is a virus that infects the liver and causes hepatitis A, an illness with an abrupt onset that can include fever, malaise, nausea, abdominal discomfort, dark urine and jaundice after a prolonged incubation period (for example, more than two months). In children less than six years old, most infections (70 percent) are asymptomatic, but in older children and adults, infection is usually symptomatic, with jaundice occurring in more than 70 percent of patients. Signs and symptoms of hepatitis A usually last more than two months, but there are no chronic consequences. About 130,000 infections with HAV and 100 deaths occur every year in the U.S.. The primary mode of transmission for HAV is person-to-person by the fecal-oral route. Recognized foodborne hepatitis A outbreaks account for only 2 to 5 percent of hepatitis A cases reported in the U.S. every year, most of which are caused by an infected food handler. Outbreaks caused by foods contaminated before preparation, while uncommon, have been associated with widely distributed products such as shellfish, lettuce, frozen raspberries and frozen strawberries. Hepatitis A can be prevented by good personal hygiene and safe food-handling practices. It can also be prevented before exposure by hepatitis A vaccine and after exposure by immunoglobulin, if it is given within 14 days of exposure.