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BACKGROUND: Investigating influenza outbreaks that occur outside of influenza season may be useful for the detection of novel viruses. In July 2013, a respiratory illness outbreak was detected during a 10-day outdoor mass gathering of 35,000 youth from the United States and 18 countries. A public health team from the West Virginia (WV) Bureau for Public Health investigated the outbreak to limit disease transmission, determine etiology of illness, and provide recommendations to the national youth organization hosting the event.
METHODS: On day one of the gathering, arriving campers were screened for rash illness, vomiting, diarrhea, fever, extreme fatigue, and international travel. On day five an outbreak of influenza-like illness (ILI) was reported by medical personnel at the camp. The public health team interviewed ill campers and collected nasopharyngeal swabs from 10 campers who met the case definition for ILI: fever ≥100°F and a cough and/or sore throat. Specimens were analyzed at the WV State Laboratory by multiplex RT-PCR and referred to CDC for subtype confirmation. To limit disease transmission, the group was relocated to an isolation camp and leaders were instructed to restrict the youth from participating in program activities until they were afebrile for 24 hours. An educational session was provided by the public health team to review CDC recommendations for hand hygiene, cough etiquette, and prevention to limit transmission of communicable disease in the camp setting.
RESULTS: In a single group of forty, ten (25%) reported ILI with one hospitalization. Predominant symptoms included cough, sore throat, malaise, and fever. Eight of ten specimens tested positive for seasonal influenza AH3; two of the specimens were not able to be tested. Subsequently, three additional cases from four other groups were reported and laboratory confirmed. Retrospectively, we identified the index case from the index group who was symptomatic upon arrival to the camp; this illness was not reported at screening.
CONCLUSIONS: Rapid response to the outbreak was important to reassure stakeholders that seasonal influenza was the etiology and to develop a response plan. Key elements of the response required communication with state and youth organization leaders, isolation of ill campers, and quarantine of the other members of the index group. Despite crowding and limited hygiene at the mass gathering, the spread of illness was controlled. Working to establish lines of communication with stakeholders and develop plans for addressing potential disease outbreaks at outdoor mass gatherings is recommended.