[Comparative characteristics of influenza type A infection in adults and children during epidemics and interepidemic periods].

Parallel serological examinations by CFT and HI test of paired sera from 18,557 patients and normal subjects in the period of influenza A/Hong Kong (H3N2) subtype virus in 1969-1976 revealed similar sensitivity of both methods for influenza diagnosis during epidemics, however in the interepidemic periods in these years the CFT was found to be more sensitive than HI. This observation referred to all age groups of the examined subjects with manifest or asymptomatic forms of influenza infection. In the interepidemic periods the rate of influenza in children was 6-8 times higher than that in adults. A sharp reduction in the HI sensitivity in the interepidemic periods indicates biological differences in influenza viruses circulating in these months of the year associated with clinical, epidemiological, and immunological features of influenza in the interepidemic period.