Asymptomatic Food Handlers Shouldn't Be Overlooked in Outbreak Investigations

Although food handlers may be asymptomatic, it is crucial for outbreak investigators to consider these individuals' role in the food preparation process, researchers say in a new study published in BMC Infectious Diseases.

Barrabeig, et al. (2010) report that in July 2005, an outbreak of acute gastroenteritis occurred in a residential summer camp in Barcelona, Spain. Forty-four people were affected among residents and employees. All of them had in common a meal at lunch time (paella, round of beef and fruit). The researchers sought to investigate a foodborne norovirus outbreak that occurred in the residential summer camp and in which the implication of a food handler was demonstrated by laboratory tests.

A retrospective cohort study was designed. Personal or telephone interview was carried out to collect demographic, clinical and microbiological data of the exposed people, as well as food consumption in the suspected lunch. Food handlers of the summer camp were interviewed. Ten stool samples were requested from symptomatic exposed residents and the three food handlers that prepared the suspected food. Stools were tested for bacteries and noroviruses. Norovirus was detected using RT-PCR and sequence analysis. Attack rate, relative risks (RR) and its 95 percent confidence intervals (CI) were calculated to assess the association between food consumption and disease.

Barrabeig, et al. (2010) report that the global attack rate of the outbreak was 55 percent. The main symptoms were abdominal pain (90 percent), nausea (85 percent), vomiting (70 percent) and diarrhea (42.5 percent). The disease remitted in 24 to 48 hours. Norovirus was detected in seven fecal samples, one of them was from an asymptomatic food handler who had not eaten the suspected food (round of beef), but cooked and served the lunch. Analysis of the two suspected foods isolated no pathogenic bacteria and detected no viruses. Molecular analysis showed that the viral strain was the same in ill patients and in the asymptomatic food handler (genotype GII.2 Melksham-like).

The researchers conclude that in outbreaks of foodborne disease, the search for viruses in affected patients and all food handlers, even in those that are asymptomatic, is essential. Health education of food handlers with respect to handwashing should be promoted.

Reference: Barrabeig I, Rovira A, Buesa J, Bartolome R, Pinto R, Prellezo H and Dominguez A. Foodborne norovirus outbreak: the role of an asymptomatic food handler. BMC Infectious Diseases 2010, 10:269doi:10.1186/1471-2334-10-269.