Comparison of the Clinical Characteristics of the Patients Visited in Emergency Department with Pandemic 2009 Influenza A (H1N1) Virus Infection during the First Three Years; An Observational Study at a Single Emergency Department

Nam, Sang Seo; Do, Byung Soo; Park, Sin Youl; Lee, Sam Beom

Abstract

PURPOSE
Daegu, Korea was severely affected by pandemic and post-pandemic H1N1 infection during August 2009 to March 2012. The aim of this study was to analyze various clinical characteristics of patients who visited the emergency department with H1N1 infection during the first three years, and to compare the results for each year. We then performed an evaluation of the differences.
METHODS
The medical records of patients who visited our emergency department and conformed to H1N1 virus infection by conventional rRT-PCR during the pandemic wave from August 2009 to March 2010(wave 1) and post-pandemic waves from August 2010 to March 2011(wave 2) and from August 2011 to March 2012(wave 3) were reviewed. A total of 986 patients (wave 1; 840, wave 2; 144, wave 3; 2) were included in this study. We analyzed the clinical characteristics, proportions of pneumonia, admission rate, relationships with underlying medical conditions, and requirement for mechanical ventilation of the infected patients, and then performed a statistical evaluation of the differences between wave 1 and wave 2 that was severely affected.
RESULTS
During wave 1,840 patients, during wave 2, 144 patients, and during wave 3, two patients were diagnosed as novel influenza. Age 18-39 showed a significantly higher rate(78.7%) in the wave 1 patients group. Main clinical symptoms were cough and febrile sense in both waves. Patients with underlying medical conditions in wave 2(97 cases, 67.4%) showed a higher rate than those of wave 1(101 cases, 12.0%). Chronic obstructive pulmonary disorder was the most closely related underlying disorder in wave 2(18.8%). Patients requiring admission(37.5%) and ventilatory care(6.9%) due to severe pneumonic symptoms showed a significantly higher rate in wave 2. Only two young patients were diagnosed as novel influenza. Both complained of mild fever and cough, which recovered spontaneously.
CONCLUSION
Most cases of influenza A (H1N1) infection were uncomplicated, characterized by influenza-like symptoms and spontaneous recovery. The number of patients showed a marked decreased year by year, however, the severity of clinical presentations increased in wave 2. Young adults who did not have cross-reactive antibodies to novel influenza A (H1N1) from previous infection or immunization were dominant in wave 1. Older patients with underlying medical conditions were more likely to admitted and present fatal progress in wave 1 and wave 2. Because influenza viruses are unpredictable, continued national preparedness, flexible response, and careful monitoring are essential.