Jun 6, 2002 (CIDRAP News) Ð A prolonged salmonellosis outbreak that affected 650 people from all 50 states was linked to a Dallas hotel food worker who was infected with Salmonella but had no symptoms, according to the Texas Department of Health (TDH).
TDH officials announced last week that they had finished an8-week investigation of the outbreak in people who had eaten at the Wyndham Anatole Hotel in Dallas in March and April. Investigation pointed to salsa made at the hotel as the vehicle for the Salmonella. The infected worker was involved in making the salsa, said Doug McBride, TDH press officer in Austin.
The TDH focused its investigation on three cohorts of people who had attended three conferences at the hotel during the period in question, according to Linda Gaul, PhD, MPH, a TDH epidemiologist in Austin. Fifty confirmed cases of salmonellosis were identified, all involving S enterica serotype Enteritidis, Gaul told CIDRAP News.
In a news release, TDH lead epidemiologist Kathleen Shupe-Ricksecker said, "We do not know how or where that first employee became infected, and we do not know for a certainty that the employee was the original source of infection. But because environmental tests in the hotel and tests of water, ice, and selected foods from the hotel were negative, our suspicion is that the employee became infected elsewhere."
The onset date of the first laboratory-confirmed case in the outbreak was Mar 16, and the last was Apr 25, Shupe-Ricksecker reported. She said nine other food workers in the hotel became ill during the outbreak and tested positive for Salmonella. McBride said some people affected by the outbreak were hospitalized, but all recovered.
The hotel management took a number of precautions in their efforts to stop the outbreak, Shupe-Ricksecker said. These included serving bottled water, buying ice from an outside source, temporarily moving the food preparation area for banquets to a secondary kitchen, and requiring food handlers to show negative tests for Salmonella before being allowed to work. Gaul said the hotel serves about 100,000meals a month.
The illness attack rate in the three cohorts investigated by the health department was about 30%, Gaul said. In its investigation, the TDH set up a password-protected Web site where members of the cohorts were invited to complete a questionnaire about their illness and possible risk factors, according to Gaul and McBride.
Gaul said asymptomatic infections with Salmonella are not highly unusual, but she couldn't estimate how often they occur in food service workers. "About 1% of adults can shed the organism for up to a year after their illness," she said. In addition, people occasionally carry a pathogen without ever having had symptoms from it, she said.
Craig Hedberg, PhD, a University of Minnesota expert on foodborne disease who formerly worked in the Minnesota Department of Health (MDH), said the MDH has done surveys of food workers in connection with a number of restaurant-related salmonellosis outbreaks. "Typically about one third ofinfected workers deny any history of illness and appear to have asymptomatic infections," he told CIDRAP News. Hedberg is an associate professor of environmental and occupational health in Minneapolis.
Hedberg commented that proper handwashing practices presumably could prevent foodborne transmission of Salmonella by food workers who are unknowingly infected, but "you probably don't need a lot of contamination" to transmit the organism.