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Original Articles
Epidemiological and Clinical Characteristics of Pandemic Influenza (H1N1 2009)
Ji Yun Noh, Sun Young Yim, Jung Yeon Heo, Won Suk Choi, Joon Young Song, Hee Jin Cheong and Woo Joo Kim
Division of Infectious Diseases, Department of Internal Medicine, Korea University College of Medicine, Seoul, Korea
Vol.42 Num.2 (p69~75)
Background: Since early outbreaks in North America in April 2009, the new influenza virus spread rapidly all over the world, and WHO declared a pandemic in June 2009. The objective of this article is to describe the epidemiological and clinical characteristics of patients confirmed with pandemic influenza (H1N1 2009).
Material and Methods: Among all patients confirmed with pandemic influenza (H1N1 2009) in Korea University Guro Hospital from 2 May 2009 to 31 March 2010, we selected 10% of patients aged more than 15 years randomly. Medical records were reviewed retrospectively and clinical findings were analyzed: social history, underlying disease, initial symptoms, and clinical course. Comparative analysis of initial symptoms was performed by time to presentation and age groups: 15-29 years, 30-49 years, 50-59 years, and more than 60 years. In addition, we described fatal cases of pandemic influenza (H1N1 2009).
Results: From 2 May 2009 to 31 March 2010, total number of laboratory-confirmed cases of pandemic influenza (H1N1 2009) was 7,888. The most cases (1,632) developed at epidemic week 46, 2009. The median age of patients was 13 years and more than half of patients (55.4%) were less than 15 years. The median time to presentation was 1 day from onset of symptom. Clinical symptoms were cough (86.9%), sore throat (69.4%), myalgia (63.3%), chill (60.6%), rhinorrhea (57.7%), headache (57.6%), nausea or vomiting (27.4%), and diarrhea (9.3%). Fever was noted more frequently at 15-29 years group than ?30 years group. Antiviral agent was administered to 274 patients (77.8%): 267 cases with oseltamivir and 7 cases with zanamivir. The median time to administration was 2 days and mean time to defervescence was 3 days. Cough was the most persistent symptom: initial visit (94.1%), on third day (82.4%), and on sixth day (52.9%) by the serial follow up at the same patients. Case fatality rate was 0.05%, and all fatal cases occurred in patients aged ?50 years.
Conclusions: Children and adolescents were the most affected group. Clinical symptoms were similar to seasonal influenza. Gastrointestinal symptoms were relatively common, and cough was the most long-lasting symptom.
Keywords : Influenza, Pandemic, H1N1, Epidemiology, Symptom