Molecular epidemiology of influenza A virus infections

Influenza is an acute respiratory disease caused by influenza viruses. Influenza virus infections are associated with high morbidity and may lead serious complications such as pneumonia. The aim of this study was to determine the incidence of influenza type A and B virus infections and influenza A virus subtypes in hospitalized patients with respiratory tract infections by real-time RT-PCR test, conventional RT-PCR test and direct immunofluorescence antibody (DFA) test. Nasopharyngeal swab specimens were collected from a total of 476 patients by using flocked swabs (Copan Diagnostics, Italy) between 1 April 2012 and 31 December 2013. Influenza A virus was detected in 20.5% (98/476) of cases and influenza B virus in 3.3% (16/476) by real-time RT-PCR test (Sacace, Italy). During the study period, 63.3% of 98 influenza virus isolates was found to be A(H1N1)pdm09 and 36.7% was A(H3N2). Influenza A (H1N1)pdm09 subtype was observed to be predominant (12 cases) in January 2013 and A(H3N2) (11 cases) in December 2013. Compared to real-time RT-PCR test, the sensitivities of DFA test (Argene SA, France) for influenza A and B and conventional RT-PCR test with WHO primers (M30F2/08 and M264R3/08) for influenza A were 72.4%, 75%, 96% and the specificities were 99.2%, 99.5% and 100%, respectively. In conclusion, influenza A virus infection was detected rather high with a rate of 20.5% in the study group. The monitoring of influenza virus types and subtypes is necessary to evaluate the match between influenza vaccine strains and circulating influenza viruses and to identify subtypes with pandemic potential. It is recommended to use real-time RT-PCR test for the early diagnosis of influenza virus infections to take effective prevention and control measures in time, to reduce unnecessary antibiotic use and to start antiviral treatment.