Background: The contribution of respiratory viruses to childhood pneumonia in tropical low- and middle-income countries is poorly understood. We used population-based respiratory illness surveillance in children 5 years of age or younger in Dhaka, Bangladesh, to characterize these illnesses.
Methods: We conducted weekly home visits to children who were referred to clinic for fever or respiratory symptoms. Standardized clinical data were collected. Nasopharyngeal washes were collected for one fifth of children diagnosed with a febrile or respiratory syndrome, with virus isolation testing for influenza and reverse transcription polymerase chain reaction testing for other viruses. Pneumonia was defined as age-specific tachypnea and crepitations on chest auscultation by study physicians.
Results: From April 2004 to February 2008, 17,584 children were followed for 17,644 child-years; 6335 children had 12,499 clinic visits with eligible illnesses, including 6345 pneumonia episodes (incidence of 36 episodes/100 child-years). Annual incidence of pneumonia/100 child-years ranged from 88.3 for children 0-6 months of age to 13.1 for those 36-60 months of age. Of 1248 pneumonia visits with laboratory testing, 803 (64%) had detection of viral pathogens, including 274 respiratory syncytial virus (22% of pneumonia visits with laboratory testing; incidence 7.9/100 child-years), 244 adenovirus (19%; 7.0/100 child-years), 198 human metapneumovirus (16%; 5.7/100 child-years), 174 parainfluenza (14.0%; 5.0/100 child-years), and 81 influenza (6.5%; 2.3/100 child years).
Conclusions: Viral pathogens contribute to a majority of childhood pneumonia episodes in Bangladesh, a setting with high pneumonia rates, especially in children 2 years of age or younger. Developing effective prevention strategies targeting these children is a high priority. Given less sensitive laboratory method used for influenza detection, influenza rates may be underestimated.