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BACKGROUND: An outbreak of febrile respiratory illness (FRI) among 126 forensic specialists attending a conference at a central Missouri hotel was reported on March 14, 2013. At the time of the report, one attendee was hospitalized with possible pneumonia and two others sought medical attention at an emergency room. Initial hypothesized causes included legionellosis, influenza, or other viral respiratory pathogen. Investigators sought to identify pathogens and possible sources of the outbreak.
METHODS: Investigators conducted a retrospective cohort study of conference attendees. Information was collected by phone interview. A case was defined as any attendee of the conference who developed fever, cough and/or sore throat between March 12 -17, 2013. Respiratory specimens from ill persons were submitted to the Missouri State Public Health Laboratory for influenza testing by reverse transcription polymerase chain reaction (RT-PCR), and to Centers for Disease Control and Prevention (CDC) for further characterization. An environmental inspection of the hotel was conducted.
RESULTS: A total of 109 (86 percent) of conference attendees were included in the analysis. Forty-two persons met the case definition (attack rate: 33 percent). Four of the cases were laboratory-confirmed (Influenza A/Victoria/361/2011-like virus). Eighty-one percent of cases were male. The age range was 35 to 81 years (median=45). The most common symptoms were: fever (100 percent), cough (100 percent), body aches (78 percent), chills (76 percent), chest pain or tightness (52 percent), and sore throat (43 percent). Seventy-eight percent of cases developed illness within 48 hours of the conference inception. Two hospitalizations but no deaths were reported. No cases were diagnosed with legionellosis, and no sources of exposure to environmental hazards (carbon monoxide, legionella bacteria or mold) were detected. One attendee who arrived at the conference exhibiting respiratory symptoms attended a pre-conference meeting on March 12th with 13 other attendees. Persons who attended this meeting in a hotel conference room without functioning ventilation had a significant increase in risk of illness (RR = 2.28, p< 0.005). The attack rate in this group was 77 percent. Influenza immunization may have been protective (RR = 0.73, p<0.15).
CONCLUSIONS: Influenza A was likely the predominant cause of the outbreak. Attendees infected during the pre-conference meeting likely became source of infection for others. This investigation highlighted several challenges with influenza prevention and control: the need for effective influenza education and increased immunization rates, encouragement of social distancing, and response to misinformation spread through social media.