The number of domestic swine flu cases hit 42 on Sunday after 34 high school and college students as well as their family members and teachers in Osaka and Hyogo prefectures were confirmed to have been infected.
The confirmations followed the discovery Saturday of Japan's first eight domestic infections of the new H1N1 flu in Hyogo. A World Health Organization expert said community-level transmission may have begun in Japan, which could lead the WHO to raise its new flu pandemic alert to the highest level of 6 from the current 5.
"We need to be fully prepared to prevent the further spread of infections," Chief Cabinet Secretary Takeo Kawamura said.