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

https://doi.org/10.1016/j.amepre.2009.10.005Get rights and content

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.

Section snippets

Background

In April 2009, Department of Defense–affiliated laboratories in San Diego and San Antonio recovered unsubtypeable influenza A virus from patient samples. The viral specimens were transported to the CDC influenza laboratory, where both viral samples were determined to be a novel influenza A virus of swine origin (nH1N1), consistent with virus isolated from patients in a Mexico influenza outbreak that began in March 2009.1 Previous novel influenza strains required 6 months or longer to establish

Setting

The USAFA, located west of Colorado Springs CO is a 4-year academic undergraduate institution that educates and trains cadets for active-duty military service as officers. Incoming students are known as basic cadet trainees (BCTs) during the summer prior to the commencement of the first academic year. BCTs are organized into squadrons of 135–140 individuals. On June 25, a total of 1376 BCTs arrived at the USAFA to begin a 6-week military training program. On July 6, active surveillance of

Descriptive Epidemiology

There were 134 confirmed and 33 suspected nH1N1 cases identified for a total of 167 incident cases. Onset dates ranged from June 26 to July 24, 2009. Case counts peaked on July 6, with 37 case patients reporting symptom onset, and the counts declined over the remainder of the outbreak period (Figure 1). The peak occurred approximately 48 hours after a 4th of July event where >1300 BCTs socialized with members of other squadrons. Among the 134 confirmed cases, 115 (86%) were BCTs; ten (7%) were

Conclusion

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 11/100 BCTs.

No deaths or hospitalizations were associated with this outbreak. BCTs undergo extensive medical screening prior to

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