Influenza cases expanded by 620,000 to hit an estimated 1.73 million in the past week beginning Jan. 29, a major Japanese newspaper reported on Sunday, citing the National Institute of Infectious Diseases. Patient numbers roared in all 47 prefectures as the nation experienced its first outbreak of H3N2, a subtype of the influenza A virus, in five years, The Japan Times reported. About 90 percent of the patients were diagnosed with the strain, the paper said. It added that some 260,000 babies and infants under 4, who were born after the previous H3N2 outbreak, had been diagnosed with the virus. According to the institute, flu infections usually peak at this time of the year.