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UNDER EMBARGO UNTIL OCTOBER 20, 2009, 12:01 AM LOCAL TIME
Novel Influenza A (H1N1) Outbreak at the U.S. Air
Epidemiology and Viral Shedding Duration
Catherine Takacs Witkop, MD, MPH, Mark R. Duffy, DVM, MPH, Elizabeth A. Macias, PhD,
Thomas F. Gibbons, PhD, James D. Escobar, MPH, Kristen N. Burwell, MPH, Kenneth K. Knight, MD, MPH
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 ribonucleicacid (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%. Twentynine 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. (Am J Prev Med 2009;xx(x):xx) Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine
On June 25, an incoming class of BCTs reported to the
USAFA originating from all 50 states and 11 foreign
countries. In July, the BCT class experienced a novel
H1N1 outbreak representing one of the largest recognized
nH1N1 clusters at a U.S. college to date. The
outbreak period incidence rate (attack rate) of confirmed
and suspected cases among the BCT class was
No deaths or hospitalizations were associated with
this outbreak. BCTs undergo extensive medical screening
prior to acceptance to the USAFA (e.g., asthma is a
disqualifying medical condition). Therefore, mild disease
severity and lack of adverse outcomes during this
outbreak may be attributable to the stringent physical
requirements for acceptance at the USAFA. The mean
duration of illness, however, was greater than 5 days,
and a small subset of cadets was subsequently diagnosed
with bronchitis and pneumonia. Furthermore, college
student populations with more heterogeneous health
conditions could experience more severe disease, including
possible mortality in those with major underlying