Epidemiological and clinical characteristics of the outbreak of 2009 pandemic influenza A (H1N1) at a middle school in Luoyang, China

Abstract

Objectives: To describe the epidemiological and clinical characteristics of 2009 H1N1 influenza, particularly the incubation period and the duration of symptoms, and to assess the public health response to this outbreak.

Study design: A retrospective cohort study was conducted among all students and employees in a middle school by telephone survey and laboratory inspection.

Methods: Nasopharyngeal specimens were collected and tested, and real-time reverse transcriptase polymerase chain reaction testing was performed to confirm the viral infection. The epidemiological and clinical characteristics were obtained through a telephone survey, and the incubation period and the duration of symptoms associated with 2009 H1N1 influenza were estimated by parametric distribution.

Results: In total, 253 cases of influenza-like illness were found among students and employees, and 79 of these cases were confirmed as H1N1 infection through laboratory inspection. The response rate for the telephone survey was 93.48% for the students (2586/2768) and 85.87% for the employees (158/184). The average attack rate was 9.22% (253/2744). The main reported symptoms were fever (100%), cough (74.68%), sore throat (59.49%), headache (56.96%) and myalgia/arthralgia (51.90%). No complications were reported and no deaths occurred. The confirmed and suspected cases had no associated travel history or contact with a confirmed or probable case. The estimated median incubation period was 1.6 days [95% confidence interval (CI) 1.2-2.3]. The duration of symptoms was 3-11 days, and the median duration of symptoms was 7.5 days (95% CI 4.5-10.5).

Conclusions: The results suggest that the outbreak of 2009 H1N1 influenza in this middle school was widespread but not severe. The natural history of 2009 H1N1 influenza virus appears to be similar to that of previously circulating pandemic and interpandemic influenza viruses. The public health response indicates that school closure could have a substantial impact on the spread of 2009 H1N1 influenza.