An Early Report from a Randomized Controlled Trial of Nonpharmaceutical Interventions to Reduce Household Influenza Transmission; the Bangkok HITS Study

Session VI – Suntarattiwong, Piyarat

Title:  An Early Report from a Randomized Controlled Trial of Nonpharmaceutical Interventions to Reduce Household Influenza Transmission; the Bangkok HITS Study

Authors: Piyarat Suntarattiwong, MD, James M. Simmerman, PhD.RN,  Jens Levy, PhD, Suchada Kaewchana, RN, MEd, Wiwan Sanasuttipun, PhD, Laurie Kamimoto, MD, Warunee Punpanich MD, Tawee Chotpitayasunondh, MD

Background: To inform pandemic and seasonal epidemic response guidelines, evidence is needed on the effectiveness of nonpharmaceutical interventions to reduce influenza transmission. We report findings from the first 176 households enrolled in a study of interventions to reduce influenza transmission in households with an influenza positive child identified in the outpatient clinic of the Queen Sirikit National Institute of Child Health in Bangkok.

Methodology: This is a block randomized (1:1:1) controlled trial of households with at least 3 members where a pediatric index patient presents with influenza-like-illness (ILI) of less than 48 hours duration. After influenza is confirmed by a rapid diagnostic test, the household is randomized to 1) control or 2) hand washing or 3) hand washing plus surgical face mask use. Households are visited by a study nurse within 24 hours and on days 3, 7 and 21. Nose and throat swabs are collected from index patients and household members at each home visit. Serum specimens are collected at days 1and 21. The primary outcome measure is PCR confirmed influenza in a household contact.

Results: Between 9 April and 31 Oct 2008, 2,362 eligible pediatric ILI patients were identified. Three hundred and sixty-three patients (15.4 %) tested influenza positive with 289 (79.6%) Type A infections. One hundred and eighty-four (50.7%) index patients and their families were enrolled and 176 households (630 persons) completed 3 home visits (Days 0/1, 3, 7). One hundred and twenty-three (71%) households had ≤4 members (mean 3.26; range 3-10) and in 118 (67%) households the index case was the only child. One hundred and fifty nine (90%) households reported that the index patient slept in the same bedroom as the parents. Sixty-six (38%) households experienced at least one secondary influenza infection on Day 3 or 7. The secondary attack ratio (SAR) was 28.6% (130/454). Compared to control households, the relative risk for a secondary influenza transmission in households randomized to the hand washing intervention was .971 (95% CI 0.60-1.56, P=.90). The relative risk for the hand washing plus surgical face mask use intervention was 1.05 (95% CI .0.66-1.66, P=1). Participants  in the hand-washing arm reported washing their hands 5.31 times/day compared to 4.61 times/day in the hand-washing plus face mask arm and 3.88 times/day in the control arm. One hundred and fifty-eight subjects reported wearing a face mask a mean of 84 minutes/day (IQR= 0-60 minutes).

Conclusions: The secondary attack ratio was higher than expected and greater than that recently reported in a similar study in Hong Kong where the majority of index patients were adults. These early data suggest poor efficacy of nonpharmaceutical interventions although poor compliance with face mask use is a concern.