Novel Influenza A (H1N1) Outbreak at the U.S. Air Force Academy. Epidemiology and Viral Shedding Duration

Background: The U.S. Air Force Academy is an undergraduate institution that educates and trains cadets for military service. Following the arrival of 1376 basic cadet trainees in June 2009, surveillance revealed an increase in cadets presenting with respiratory illness. Specimens from ill cadets tested positive for novel influenza A (H1N1 [nH1N1])-specific ribonucleic acid (RNA) by real-time reverse transcriptase-polymerase chain reaction. Purpose: The outbreak epidemiology, control measures, and nH1N1 shedding duration are described. Methods: Case patients were identified through retrospective and prospective surveillance. Symptoms, signs, and illness duration were documented. Nasal-wash specimens were tested for nH1N1-specific RNA. Serial samples from a subset of 53 patients were assessed for presence of viable virus by viral culture. Results: A total of 134 confirmed and 33 suspected cases of nH1N1 infection were identified with onset date June 25-July 24, 2009. Median age of case patients was 18 years (range, 17-24 years). Fever, cough, and sore throat were the most commonly reported symptoms. The incidence rate among basic cadet trainees during the outbreak period was 11%. Twenty-nine percent (31/106) of samples from patients with temperature <100°F and 19% (11/58) of samples from patients reporting no symptoms for ≥24 hours contained viable nH1N1 virus. Of 29 samples obtained 7 days from illness onset, seven (24%) contained viable nH1N1 virus. Conclusions: In the nH1N1 outbreak under study, the number of cases peaked 48 hours after a social event and rapidly declined thereafter. Almost one quarter of samples obtained 7 days from illness onset contained viable nH1N1 virus. These data may be useful for future investigations and in scenario planning.