The impact of household environments and daily activities on acute respiratory illness in community-dwelling older people

Abstract

Background: Acute respiratory illness (ARI) shows different seasonal variations across regions. Ambient environmental factors, such as temperature and humidity, have been associated with ARI incidence in temperate regions, but the findings were less consistent in tropical and subtropical regions. This inconsistency might be due to the lack of indoor environmental data in previous studies. Objectives: The study aimed to: (1) investigate the associations between indoor and outdoor environmental factors, including temperature, relative humidity (RH), absolute humidity (AH), and temperature variability (TV); (2) estimate the impacts of indoor environmental factors on the incidence of self-report ARI in community-dwelling older people; (3) explore the effect modification of daily activities on the association between indoor environmental factors and ARI incidence. Methods: A prospective cohort study of community-dwelling older adults (aged 65 years or above) was conducted from December 2016 to May 2019 in Hong Kong Island. Household temperature, RH and ARI episodes were continuously collected from each participant. AH was measured by vapour pressure converted from temperature and RH. TV was calculated by standard deviations of hourly temperature. Participants were invited to wear GPS tracking devices for one week in the warm and cool seasons, respectively to collect their daily activity patterns. Participants were classified into more time at home and less time at home according to their daily average hours out of home. A time-stratified case-crossover analysis with conditional logistical regression was used to estimate the excess risks (ER) of ARI incidence associated with indoor and outdoor environmental factors. Stratified analyses by seasons and daily activity patterns were subsequently conducted. Results: A total of 285 participants were recruited. During an average follow-up period of 608 days, a total of 168 ARI episodes were reported from 112 participants. Of them, 6 and 4 participants were tested positive for influenza A and RSV, respectively. Indoor temperature, RH and AH had higher correlations with the corresponding outdoor data in the cool season, and moderate correlations in the warm season. Indoor environmental factors had larger variations across households in the warm season than in the cool season. The cumulative ER of ARI incidence associated with per 1 unit (mb) increase of indoor AH was observed over six lag days (ER: -8.9%, 95% CI: -15.9%, -1.4%) in the cool season. Indoor temperature and RH were negatively associated with ARI, but were less consistent compared with indoor AH. There was a marginally positive association between indoor TV and ARI, with a 3-day cumulative ER of 116.3% (95% CI: -3.2%, 383.4%) in the cool season. GPS data from 186 participants showed that these participants spent an average of 3.3 hours out of home per day. Amplified ER estimates of indoor and outdoor AH were found among participants who spent less time at home as compared to those spent more time. Conclusion and Implication: This is the first prospective cohort study to evaluate the impact of indoor environmental factors and daily activities on ARI incidence. Lower indoor AH was independently associated with a higher risk of ARI in older people, particularly in the cool season. A higher level of daily activity may amplify the effect of AH on ARI risks. These findings add important evidence to understand the seasonal ARI activities in subtropical regions. More research is warranted to elucidate the effect modification of daily activity on environmental factors with larger sample size.