Seasonal Outbreak of Influenza A virus Infection in Pediatric Age Groups During 2004-2005 in South of Iran

Background: the pandemic and regional influenza outbreaksresulting from antigenic variation of influenza viruseshave been the subject of numerous studies which are crucialto the preparation of the vaccine. frequent global winter outbreaksof influenza viruses require a constant surveillance ofemerging influenza variants in order to develop efficient influenzavaccine.methods: this study was conducted from december 2004 tomarch 2005, during an outbreak of influenza in 300 childrenof one to 15-year-old. mock cells grown in microwellplates inoculated with pharyngeal swabs. hemagglutination(ha) of guinea pig erythrocytes by viral isolates was used forinitial screening of influenza viruses. the final viral identificationwas performed by ha inhibition test using reference antiseraprepared against who reference antigens.results: based on the results of ha tests with culture fluid ofmock inoculated with 300 pharyngeal swabs, 31 (10.3%) ofthe specimens were suspected to contain influenza viruses ofwhich 10 proved to be either a/h1n1or a/h3n2 subtypes. byreacting against aforementioned antisera in ha inhibition test.h3n2 subtype prevailed until january 2005 and mostlyaffected children of younger age, whereas viruses emergingsubsequently were only of h1n 1 subtype and predominantlyisolated from children of older age.conclusion: a/h3n2 isolate appears to be antigenically differentfrom corresponding reference antigen. this is evident by a16-fold reduction in antibody titer by using reference antiserumagainst a/h3n2 isolate (i :8), as compared to that of referenceantigen antibody (i: 128).