There were three exposures with p-values below 0.1: vaccination, having a car in the household and having three or more children at home (Table 3) . Household contacts increased the unadjusted risk of SCII ( Figure  2 ). Attack rates were lowest in those living alone (4%), intermediate in those living with adults but no children (10%) or one or two children (12%), and highest in those with three or more children in the household (24%). In a stratified analysis, the effect of car ownership was significant when participants did not live with children (RR = 2.77, p = 0.01), but not for participants who lived in a household with children (RR = 0.98, p = 1.00).