A clinical attack rate below 1.4% due to pH1N1 has been estimated for the spring of 2009 in the US [39] , a clinical attack rate of 7.5% has been estimated in New Zealand for the entire influenza season between April and August 2009 [40] and in England the estimated clinical attack rate was 10 times lower than the cumulative incidence of infection of 20% suggested from serosurveys of 15-24 year olds [41] . We suggest that a relatively low clinical attack rate -but a much higher infection rate -by a virus causing generally mild disease would allow community transmission of the virus to go unrecognised for many weeks. We further suggest that this occurred in Mexico and Victoria and may indeed have occurred in other countries [42] . Radiological and Clinical Characteristics of a Military Outbreak of Pandemic H1N1 2009 Influenza Virus Infection OBJECTIVE: To describe detailed clinical and radiological features of the pandemic H1N1 2009 influenza viral infection among healthy young males in a semi-closed institutionalized setting. MATERIALS AND METHODS: A total of 18 patients confirmed with the pandemic H1N1 2009 influenza virus infection from July 18 to July 30, 2009 were enrolled in this study. Each patient underwent an evaluation to determine detailed clinical and radiological features. RESULTS: All patients presented with high fever (> 38.0℃), with accompanying symptoms of cough, rhinorrhea, sore throat, myalgia and diarrhea, and increased C-reactive protein (CRP) values with no leukocytosis nor elevated erythrocyte sedimentation rate (ESR). All patients, including one patient who progressed into acute respiratory distress syndrome, were treated with oseltamivir phosphate and quickly recovered from their symptoms. Chest radiographs showed abnormalities of small nodules and lobar consolidation in only two out of 18 patients. However, six of 12 patients who underwent thin-section CT examinations showed abnormal findings for small ground-glass opacities (GGOs) in addition to poorly-defined nodules with upper lobe predominance. CONCLUSION: In a population of healthy young adults, elevated CRP with normal ESR and white blood cell levels combined with GGOs and nodules on thin-section CT scans may indicate early signs of infection by the pandemic H1N1 2009 influenza virus. I individuals live in close contact and have higher reported rates of viral infections (14) . Furthermore, there have been a few reports providing detailed descriptions of the radiologic features of the pandemic H1N1 2009 influenza virus infection such as in thin-section CT (11) (12) (13) .