Household Size and Age as Primary Drivers of COVID-19 Infection Among Priority Populations in Australia

Background The COVID-19 pandemic exacerbated health disparities globally, with certain populations experiencing disproportionate disease burdens. In Australia, COVID-19 deaths occurred disproportionately among first-generation migrants. This study examined risk factors for COVID-19 infection in a Victorian cohort recruited from priority populations, including healthcare workers, people with chronic health conditions, and culturally and linguistically diverse (CALD) communities. Methods We conducted a cross-sectional analysis of participants from the Optimise longitudinal cohort study (September 2020-December 2023). The primary outcome was the self-reported count of confirmed COVID-19 infections (PCR or rapid antigen test positive) from December 2019 to December 2023. We used Poisson regression to examine associations between baseline sociodemographic characteristics and infection count, calculating unadjusted and adjusted incidence rate ratios (IRRs) with 95% confidence intervals (CIs). Results Of 433 participants (median age 51 years, 75% female), 25% reported no infections, 48% reported one infection, and 27% reported two or more infections. In univariate analysis, CALD status (IRR=1.24,95%CI:1.02-1.50) and larger household size (2-5 people, IRR=1.71,95%CI:1.14-2.50) were associated with higher infection rates, while chronic health conditions (IRR=0.73, 95%CI:0.61-0.88) and older age (IRR=0.54, 95%CI:0.43-0.67) were associated with lower infection rates. In adjusted analysis, younger age (18-34 years vs [≥]55 years: aIRR=0.63,95%CI:0.48-0.82) and medium household size (living alone vs 2-5 person household: aIRR=1.42, 95%CI:1.11-1.83) remained significant predictors. CALD status and socioeconomic status showed no independent association with infection risk after adjustment for household size and age. Conclusion COVID-19 infection risk in this Victorian cohort was driven by younger age and larger household size rather than CALD status or socioeconomic status, suggesting that housing density and age, rather than cultural or socioeconomic characteristics, determined infection patterns. Future pandemic preparedness should prioritise policies enabling safe quarantine and isolation for individuals in larger households and workplace protections and economic security for younger essential workers.