Variables significantly associated with SCII were the type of household contact environment, car ownership, and vaccination status (Table 4 ). Living with children was associated with an increased risk of SCII, with an overall odds ratio of 3.7 (p < 0.01, separate model without stratification of household contacts). Three or more children in the household (OR13.8, p < 0.01) were a greater risk than one or two children (OR 5.3, p = 0.02).