Selected socio-demographic characteristics of eligible sub-cohorts at baseline (n = 1020) and 3 mo. visit (n = 771).

1 One participant with no recorded age;2 Travel in the three months preceding baseline clinic visit was categorised as: Low (zero nights away from home), Moderate (≥1 night but less than one continuous week away from home) and High (≥1 continuous week away from home on one or more occasions);3 Permanence of home and workplace location was categorised as: High (lived in the same house and worked at the same facility during the past year); Moderate (lived or worked at the same location for