Background:
It remains unclear whether both environmental factors and daily mobility would modify the risk of acute respiratory illness (ARI). The study aimed to investigate the effect modification of daily mobility pattern on the risk of ARI associated with environmental factors, including temperature, relative humidity (RH), absolute humidity (AH) among community-dwelling older people.
Methods:
From Dec 2016 to May 2017, 285 community-dwelling older adults in Hong Kong were recruited and followed up till May 2019. The household indoor temperature and RH of individual participant were continuously monitored by data loggers and their acute respiratory symptoms by monthly telephone surveys. Outdoor environmental data were retrieved from the Hong Kong Observatory. Participants’ daily mobility patterns were measured by GPS devices for seven consecutive days in the summer and winter of 2018. Participants were classified into the large and small life space groups using the cut-off of median daily travel distance from home in summer and winter, respectively. A time-stratified case-crossover design with conditional logistical regression was used to estimate the 7-day cumulative excess risk (ER) and 95% confidence interval (CI) of ARI associated with per unit increase of both indoor and outdoor environmental factors. The interaction of daily mobility and environmental factors were measured by stratification analysis of two mobility groups.
Results:
A total of 186 participants had complete GPS data collection at least in one season, including 154 in summer and 168 in winter. The median daily travel distance from home were 1.4 and 2.3 kilometres in summer and winter, respectively. There were 81 participants who reported a total of 99 ARI episodes during the study period. A negative association was found between outdoor AH and ARI incidence, which was amplified higher in the small life space group than in the large life space group (cumulative ER -13.8% vs -4.8%). No significant difference between two life-space groups was observed for indoor or outdoor temperature and RH and indoor AH.
Conclusions:
Small life space might have comprised the hazards of by of ARI associated with lower outdoor AH, but no such evidence was found for other environmental factors.

environmental impact,Mobility,Daily activity,Acute respiratory illness