In our series, most patients (15 out of 18) were from the same barrack, a semi-closed setting; whereas, the three remaining patients from different barracks were thought to be infected from these 15 patients. All patients were healthy young males without any combined chronic disease. Clinical and laboratory results from this homogeneous study population can be helpful in understanding the clinical characteristics of the pandemic H1N1 2009 influenza virus infection in semi-closed settings and in institutionalized populations composed of a young healthy population, such as in schools, dormitories, prisons, or military units. Furthermore, this report demonstrated that a prompt diagnosis and treatment resulted in excellent outcomes and could provide as an example for the detection and management strategy for cluster outbreaks of this virus. However, there may be limitations in applying these results to the larger general population.