Characterization and epidemiology of influenza viruses in patients seeking treatment for influenza-like illnesses in rural Bangladesh

CONTEXT: Infections caused by influenza viruses are a major health burden, both in developed and developing countries worldwide. Nevertheless, the overwhelming majority of influenza reports originate from industrialized countries in northern and southern temperate zones.

AIMS: The aim of this study was to determine the epidemiology of influenza viruses in patients seeking treatment for acute febrile illnesses in rural Bangladesh.

SETTINGS AND DESIGN: As part of our research on the causes of febrile illnesses in rural Bangladesh, nasopharyngeal swabs from patients with signs and symptoms consistent with influenza were collected from 2008 onwards.

MATERIALS AND METHODS: Viral infection was established using two independent rapid diagnostic tests (RDTs) and later confirmed by RT-PCR.

RESULTS: A total of 314 fever cases were enrolled in a survey of febrile illnesses carried out in Bandarban District in southeastern Bangladesh, out of whom 38 (12.1%) tested positive by RDT. Molecular subtyping showed that seasonal H3 strains (N=22; 7.0%) as well as the new H1N1v pandemic influenza subtype (N=13; 4.1%) had been circulating at the time of our investigations resulting in a PCR-adjusted positivity rate of 11.1% (95% CI 8.0 - 15.3). The positive predictive values for the RDTs used were 90.9% and 94.4%, respectively.

CONCLUSIONS: This study provides a first insight into influenza epidemics in one of the most remote parts of Asia. Our findings suggest that respiratory illnesses due to influenza viruses are underreported in areas with limited access to health care and show a distinct seasonality also in rural areas of tropical countries.