Pilot findings of a cluster randomized trial of non-pharmaceutical interventions for influenza prevention in households in Hong Kong

Abstract

Background: There are sparse data on the efficacy of non-pharmacological interventions for prevention of influenza virus transmission. We implemented a pilot study of the feasibility and efficacy of masks and hand hygiene to reduce transmission in Hong Kong households (February to September 2007) as part of a larger community trial planned for 2008. Methods: We conducted a cluster randomized controlled trial of households (composed of at least 3 members) where an index subject presented with influenza-like-illness of <48-hour duration. After confirmation as influenza by the QuickVue Influenza A+B rapid test, the household was randomized to 1) control group or 2) surgical masks or 3) hand hygiene. Households were visited within 36 hours, and again 3, 6 and 9 days later. Nose and throat swabs were collected from index subjects and household contacts at each home visit and tested by viral culture. The primary outcome measure was laboratory confirmed influenza in a household contact; secondary outcome was clinical influenza (by self-reported symptoms). Results: We randomized 198 households and completed follow up home visits in 128 households. There were 23 household contacts with laboratory confirmed influenza and 41 with clinical influenza, corresponding to secondary attack ratios of 4% and 8% respectively. The secondary attack ratios did not significantly differ across the intervention groups. In multivariable regression models, history of influenza vaccination and younger age of the corresponding index subject were associated with lower risk of secondary infection, but were not statistically significant at the 0.05 level. Conclusions: The secondary attack ratios were lower than anticipated, and lower than in previous studies in Western settings, perhaps due to differing patterns of susceptibility, lack of significant viral strain drift, and/or issues related to the symptomatic recruitment design.