Norovirus most common cause of foodborne illness

Scallan E. Emerg Infect Dis. 2011;17:7-15.

An estimated 31 major pathogens acquired in the United States are responsible for 9.4 million instances of foodborne illness, according to a study reported in Emerging Infectious Diseases.

These same pathogens are responsible for 55,961 hospitalizations and 1,351 deaths, researchers from the CDC estimated.

“Estimates of the overall number of episodes of foodborne illness are helpful for allocating resources and prioritizing interventions,” the researchers wrote. “However, arriving at these estimates is challenging because food may become contaminated by many agents, transmission can occur by nonfood mechanisms, the proportion of disease transmitted by food differs by pathogen and by host factors, and only a small proportion of illnesses are confirmed by laboratory testing and reported to public health agencies.”

The researchers used data from active and passive surveillance and other sources to determine the estimates of foodborne illness and its causes. Most of the data were from 2000 to 2008. All estimates were based on the US population in 2006.

They estimated that each year, 31 pathogens caused 36.4 million domestically acquired illnesses, and 9.4 million of these illnesses were foodborne. An estimated 5.5 million foodborne illnesses were caused by viruses; 3.6 million by bacteria; and 200,000 by parasites. Norovirus caused 58% of the illnesses. Non-typhoidal Salmonella spp. caused 11% of the illnesses; Clostridium perfringens caused 10%; and Campylobacter spp. caused 9%.

The 31 pathogens caused an estimated 228,744 hospitalizations, annually. Of these, 55,961 were caused by food eaten in the United States. Of those, 64% were caused by bacteria; 27% by viruses; and 9% by parasites. The most common causes of hospitalization were non-typhoidal Salmonella spp., norovirus, Campylobacter spp. and Toxoplasma gondii.

Researchers further estimated that the 31 pathogens caused 2,612 deaths. Of these, 1,351 were caused by foods eaten in the United States. Among those, 64% were caused by bacteria; 25% by parasites; and 12% by viruses. The most common causes of death were non-typhoidal Salmonella spp., T. gondii, Listeria monocytogenes and norovirus.

“The estimates from this study can be used to help direct policy and interventions, to conduct other analyses, and as a platform for developing estimates of effects of disease caused by sequelae of foodborne infections,” the researchers wrote.

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