[Relationship between absolute humidity and influenza prevalence in Odate and Akita cities, Akita Prefecture, in 2001 and 2002].

The dynamics of influenza viruses in relation to one meteorological factor, absolute humidity, was investigated. The number of influenza patients, absolute humidity, and isolation of influenza viruses were compared between Odate City the north and Akita City in central Akita Prefecture from 2001 to 2002. The results were as follows: 1) In both Odate and Akita cities, Influenza A (H1N1 and H3N2) and Influenza B (Victoria and Yamagata) viruses were isolated when absolute humidity ranged between 2.7 and 8.8 g/m3. 2) In Akita City in 2002, the influenza viruses were isolated in May (weeks 20 and 22), and the absolute humidity was below 9 g/m3, suggesting that the influenza season lasted until May in this year. 3) A correlation between absolute humidity and isolation of influenza viruses was observed, and the influenza prevalence may occur below 9 g/m3 of absolute humidity. 4) In Odate and Akita cities, the absolute humidity of 10 g/m3, a level at which 5% of influenza viruses can survive after six hours, was observed from January to June and October to December. 5) Influenza prevalence show differential occurrence by time and place. Therefore, further research is required to clarify the absolute humidity related to influenza prevalence.