Indoor Environmental Factors and Influenza-Like Illness in Community Dwelling Older Population of Hong Kong: A Prospective Cohort Study

Abstract

Background: Previous studies have investigated the impacts of outdoor environmental factors (temperature, relative humidity (RH), absolute humidity (AH), rainfall) on seasonal variations of influenza virus activities. However, the findings were inconsistent to explain the circulation and summer surge of influenza in tropical and subtropical regions. We hypothesize that the controversial findings might be due to the lack of indoor environmental data. We conducted a prospective cohort study in community dwelling older people in Hong Kong to explore the relationship of indoor and outdoor environmental factors with incidence of influenza-like illness (ILI) in older people.Methods: A total of 231 older people aged 65+ years in the Hong Kong Island were recruited as index participants from Dec 2016 - Apr 2017. Automatic sensors were installed in the living room of each household to continuously collect the hourly indoor temperature and RH during the study period. The follow-up is still ongoing and expected to end by May 2019.Results: Here we report the preliminary findings of the first-year follow-up data from Dec 2016 - Mar 2018. Mean indoor temperature, RH and AH were 24.4°C, 68.1% and 22.2g/m3 respectively. Indoor temperature and AH were highly correlated with outdoor temperature (r=0.95) and AH (r=0.95). While, indoor RH varied widely during June to September (difference 10.8% ± 48.3) and less correlated with outdoor RH (r=0.67). The incidence rate of self-report influenza-like illness was 0.4 per person-year, and most were reported during May - Aug 2017 and Dec 2017 - Feb 2018. Preliminary results showed there was no significant difference between households with and without ILI cases, in terms of indoor environmental factors such as daily mean, minimum, median, maximum, variation of temperature, RH and AH.Discussion: Indoor-outdoor correlation was found high for temperature and AH but moderate for RH. Further analyses will be conducted when more data are collected.