Influenza Virus Contamination of Common Household Surfaces during the 2009 Influenza A (H1N1) Pandemic in Bangkok, Thailand: Implications for Contact Transmission

Background. Rational infection control guidance requires an improved understanding of influenza transmission. We studied households with an influenza-infected child to measure the prevalence of influenza contamination, the effect of hand washing, and associations with humidity and temperature. Methodology. We identified children with influenza and randomly assigned their households to hand washing and control arms. Six common household surfaces and the fingertips of the index patient and symptomatic family members were swabbed. Specimens were tested by real-time reverse-transcription polymerase chain reaction (rRT-PCR), and specimens with positive results were placed on cell culture. A handheld psychrometer measured meteorological data. Results. Sixteen (17.8%) of 90 households had influenza A-positive surfaces by rRT-PCR, but no viruses could be cultured. The fingertips of 15 (16.6%) of the index patients had results positive for influenza A, and 1 virus was cultured. Index patients with seasonal influenza infections shed more virus than did patients with pandemic influenza infection. Control households had a higher prevalence of surface contamination (11 [24.4%] of 45) than did hand washing households (5 [11.1%] of 45); prevalence risk difference (PRD), 13.3%; [95% confidence interval {CI}, -2.2% to 28.9%];). Households in which the age P = .09 of the index patient was <= 8 years had a significantly higher prevalence of contamination (PRD,19.1%; 95% CI, 5.3%-32.9%; P = .02). Within the strata of households with secondary infections, an effect of lower absolute humidity is suggested (P = .07). Conclusions. We documented influenza virus RNA contamination on household surfaces and on the fingertips of ill children. Homes with younger children were more likely than homes of older children to have contaminated surfaces. Lower absolute humidity favors surface contamination in households with multiple infections. Increased hand washing can reduce influenza contamination in the home.