OBJECTIVES: This report describes the results of an investigation on an outbreak of novel influenza A (H1N1) in an English language Institute in Seoul, Korea in May 2009. METHODS: In this outbreak, novel influenza A (H1N1) was confirmed in 22 of 91 trainees, trainers and staff members. The trainees and 2 staff members were isolated in an assigned facility and the rest were isolated in their homes after we discovered the first patient with novel influenza A (H1N1). After the isolation, the people in the assigned facility were educated to use N95 respirators and they received oseltamivir for prophylaxis. RESULTS: The initial findings in this study suggest that the symptoms were mild and similar to those of seasonal influenza. The classmates and roommates of the infected patients were more likely to get infected with novel influenza A (H1N1) than the trainees who were not classmates or roommates of the patients (OR: 3.19, 95% CI=0.91 - 11.11 for classmates and OR: 40.0, 95% CI=7.4-215.7 for roommates). CONCLUSIONS: The public health response seems successful in terms of preventing the spread of this virus into the local community.
Adult ; *Disease Outbreaks ; Humans ; Influenza A Virus, H1N1 Subtype/*isolation & purification ; Influenza, Human/diagnosis/drug therapy/*epidemiology/physiopathology ; Republic of Korea/epidemiology ; *Schools ; Young Adult

The pandemic H1N1/09 emerged rapidly in Korea. Here, we describe the clinical characteristics of outpatients in Seoul, Korea who were infected in the 2009 H1N1 pandemic. We reviewed the cases of outpatients with pandemic H1N1/09 who visited a tertiary care teaching hospital between September 1 and December 31, 2009. Infection with pandemic H1N1/09 was confirmed by molecular tests. Of a total of 7,182 tests, 3,020 (42.0%) were positive. Compared with 473 cases of influenza-like illness (ILI), the 586 confirmed cases of pandemic H1N1/09 differed in age [odds ratio (OR) 0.975] and fulfilling at least one of the following factors: age <5 or > or =65 years, history of contact with other pandemic H1N1/09-infected individuals (OR 0.611), fever > or =37.8degrees C (OR 3.567), cough (OR 2.290), and myalgia (OR 1.559). The sensitivity of the best criteria, "fever (> or =37.8degrees C) plus cough" (41.03%) in this study was lower than that of the Korea Centers for Disease Control and Prevention (KCDC) criteria (47.95%), whereas the positive likelihood ratio (3.55) and positive predictive value (81.6) of this criteria was higher than those of the KCDC criteria (2.98 and 78.7, respectively). The clinical characteristics of pandemic H1N1/09 are, in many regards, indistinguishable from those of ILI. Moreover, the accuracy and predictability of criteria which include only symptoms or signs were not sufficient to diagnose pandemic H1N1/09 infection. Therefore, use of a combination of symptoms with confirmatory laboratory testing is necessary for accurate diagnosis of pandemic H1N1/09.
Adolescent ; Adult ; Child ; Comorbidity ; Female ; Hospitals, University/statistics & numerical data ; Humans ; *Influenza A Virus, H1N1 Subtype ; Influenza, Human/*diagnosis/*epidemiology/physiopathology ; Male ; Multivariate Analysis ; Outpatients/*statistics & numerical data ; Pandemics/*statistics & numerical data ; Republic of Korea/epidemiology ; Risk Factors ; Young Adult