Household-level risk factors for influenza among young children in Dhaka, Bangladesh: A case-control study

Objectives: To identify household-level factors associated with influenza among young children in a crowded community in Dhaka, Bangladesh. Methods: We conducted a case-control study using existing active surveillance for respiratory illness. Cases were children aged 12-59 months with laboratory-confirmed influenza. Controls were children frequency-matched by age group with no respiratory illness in the prior 6 months. We interviewed caregivers and observed household handwashing behaviour. Soap consumption was estimated by summing weight differences of three bars of soap sequentially left in each household. We measured concentrations of airborne particulate matter <2.5 μg in diameter (PM_2.5) in a subset of households. We used logistic regression to estimate adjusted odds ratios (aOR) and 95% confidence intervals (CI). Results: We enrolled 145 cases and 341 controls between March 2009 and April 2010. Case and control household members were observed to wash hands with similar frequency during a 5-h period (mean, 0.64 events vs. 0.63, P = 0.87), and similar daily soap consumption per capita (mean 2.92 grams vs. 2.93, P = 0.92). Case households were more likely than controls to have crowded (≥4 persons) sleeping areas (aOR = 1.67, CI: 1.06-2.63) and cross-ventilated cooking spaces (aOR = 1.75, CI: 1.16-2.63). Case and control households had similar median 24-h geometric mean PM_2.5 concentrations in the cooking (69.2 vs. 69.6 μg/m³, P = 0.45) and sleeping (65.4 vs. 67.4 μg/m³, P = 0.19) spaces. Conclusions: Handwashing with soap was practiced infrequently and was not associated with paediatric influenza in this community. Interventions aimed at crowded households may reduce influenza incidence in young children.