Genetic evidence for containment of viruses in the first outbreak of influenza A pandemic (H1N1) 2009 in Kobe, Japan

BACKGROUND On 16 May 2009, a high school student in Kobe with no history of overseas travel was reported as the first case of influenza A pandemic (H1N1) 2009 virus infection in Japan. Subsequently, it was revealed that the infection had spread to some cities in the Kansai region and most patients were high school students. The number of patients decreased rapidly within a week; however, it began to increase in the middle of July. METHODS We phylogenetically analyzed viral characteristics using 27 viruses isolated from patients living in Kobe. RESULTS AND CONCLUSIONS We demonstrated that viruses isolated in the early phase of the outbreak were distinguishable from those after the reappearance of patients. These findings provide genetic evidence for the effectiveness of public health containment measures in the Kansai region in preventing the progression of the outbreak.