Influenza B virus outbreak at a religious residential school for boys in Northern Bangladesh, 2011.

BACKGROUND: National media reported a febrile illness among dormitory residents of a boys' religious school. We investigated the outbreak to identify cause. METHODS: Individuals with fever (>100°F) and cough or sore throat between 1 and 13 August 2011 were influenza-like-illness (ILI) case-patients. We collected histories and specimens from hospitalized case-patients and visited campus to explore environmental context. RESULTS: All 28 case-patients were dormitory residents including 27 hospitalizations. Accommodation space per resident was <0.8 square metres. Nasal and oropharyngeal swabs from 22 case-patients were positive for influenza B virus using real-time reverse transcription polymerase chain reaction (rRT-PCR). CONCLUSIONS: Overcrowding likely facilitated transmission leading to this dormitory outbreak.