• Chang Hwan Sohn, Seung Mok Ryoo, Ji Young Yoon, Dong Woo Seo, Kyoung Soo Lim, Sung Han Kim, Sang Bum Hong, Chae Man Lim, Youn Suck Koh, and Won Young Kim.
• Department of Emergency Medicine, Ulsan University College of Medicine, Asan Medical Center, Seoul, Korea.
• Acad Emerg Med. 2013 Jan 1; 20 (1): 46-53.

ObjectivesA novel swine-origin influenza A (H1N1) virus caused worldwide outbreaks starting in April 2009. The aim of this study was to evaluate the clinical characteristics and outcomes of pandemic 2009 H1N1 pneumonia by comparing to community-acquired pneumonia (CAP) of other origin.MethodsThe authors conducted a prospective cohort study of consecutive adult (over 15 years old) patients with suspected CAP requiring admission to a tertiary university-affiliated hospital during the second wave of pandemic 2009 H1N1 influenza. Based on the results of real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, the staff completed a standard assessment form and managed the patients according to a uniform protocol. Clinical characteristics, as well as laboratory and radiologic findings, were collected and compared between pandemic 2009 H1N1 pneumonia and CAP of other origin. The primary outcome was in-hospital mortality and secondary outcomes were duration of hospitalization, duration of intensive care unit (ICU) stay, and requirement of mechanical ventilation.ResultsA total of 135 patients with suspected CAP were included in the study. Of these, 59 patients were RT-PCR positive for H1N1 virus, and 76 patients were RT-PCR negative. Patients with H1N1 pneumonia were significantly younger than those with CAP of other origin (46.0 years vs. 68.0 years, p < 0.01) and more frequently had nonspecific symptoms (p < 0.01), initial leukopenia (8.5% vs. 0.0%, p = 0.01), lymphopenia (45.8% vs. 26.3%, p = 0.02), low values of C-reactive protein (CRP; 5.2 mg/dL vs. 13.4 mg/dL, p = 0.02), bilateral abnormalities (57.7% vs. 29.7%, p < 0.01) on chest radiography, ground glass opacities (43.9% vs. 12.8%, p < 0.01) on chest computed tomography, and low values of pneumonia severity index (PSI) score (56.0 vs. 91.0, p < 0.01) than those with CAP of other origin. However, there were no significant differences in infection severity, clinical outcome, length of ICU stay, requirement for mechanical ventilation, and mortality between the two groups.ConclusionsThis study shows that clinical characteristics and outcomes of 2009 H1N1 pneumonia are comparable to those of CAP of other origin. However, some characteristics, including younger age, nonspecific symptoms (including headache, leukopenia, and fatigue), lymphopenia, lower initial CRP and PSI score, and radiologic findings (including bilateral abnormalities and ground glass opacities), may help clinicians to diagnostically differentiate between H1N1 pneumonia and CAP of other origin before the result of RT-PCR are obtained.© 2013 by the Society for Academic Emergency Medicine.

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