Epidemiologic Characteristics of Pandemic H1N1 Influenza in 2009: An Observational Study at a Single Emergency Department

Jung, Joo; Ro, Young Sun; Lee, Eui Jung; Shin, Sang Do; Kwak, Young Ho; Suh, Gil Joon

Abstract

PURPOSE
This study was designed to determine the epidemiological and clinical characteristics of patients suspected or confirmed with to be infected by the pandemic 2009 H1N1 virus in one emergency medical center.
METHODS
This was a prospective observational study. It was conducted between September 1 and November 30, 2009 in one tertiary academic emergency department. We recorded clinical and epidemiologic features of patients infected by the pandemic 2009 H1N1 virus. A follow-up telephone survey was done to determine the final outcome of infection. This survey was conducted by ED personnel 1 week after the initial visit. Multivariate logistic regression analysis was done for the association between disposition or H1N1 influenza diagnosis and potential predictors.
RESULTS
During the study period, a total 5,317 patients visited the influenza clinical center of our emergency department. Among them, 1,472 patients (27.7%) were confirmed as influenza A by RT-PCR methods. Among RT-PCR positive patients, 90 (1.7%) were admitted to the ward and 7 to the intensive care unit. Five patients needed mechanical ventilation and one patient was diagnosed as ARDS; the ARDS patient fully recovered. There was no mortality caused by H1N1. The median age of confirmed patients was 9 years (range, 1 month~81 years); 825 patients (56.1%) were male. Incident rates for common symptoms were: fever (92.8%), cough (84.1%), and rhinorrhea (44.0%) by. A total of 40.3% (593/1472) patients were of pre-school age (range, 1 month~7 years, median 4 years). In young patients, clinical characteristics were similar to those of adults. Male, young age, contact history, lack of seasonal influenza vaccination, chronic renal failure, malignancy, and pregnancy were significantly associated with a confirmed diagnosis of H1N1. Hypertension, chronic renal failure, malignancy, neurologic disease, dyspnea, seizure, vomiting, and chest pain were also associated with risk of admission to the hospital.
CONCLUSION
Surveillance of H1N1 virus cases shows that the majority of those infected have a mild illness. The 2009 H1N1 virus is common among individuals of pre-school age. Few H1N1-related severe illnesses occur in young individuals.