Viruses causing lower respiratory symptoms in young children: findings from the ORChID birth cohort

Sarna, Mohinder; Lambert, Stephen B; Sloots, Theo P; Whiley, David M; Alsaleh, Asma; Mhango, Lebogang; Bialasiewicz, Seweryn; Wang, David; Nissen, Michael D; Grimwood, Keith; Ware, Robert S

The incidence rate of single new virus detection episodes (VDEs) per 100 child-years was calculated using Poisson regression. To account analytically for the differing lengths of time children remained in the study, the natural logarithm of the number of swabs returned was included in the model as an offset. Swabs were removed from incidence rate calculations for individual viruses when the participant was not at risk of a new VDE (a positive consecutive swab following the initial positive swab, and two swabs after the last positive swab, as per our definition of a new VDE), or the swabs were of lesser quality (to avoid underestimating incidence rates). 21 When calculating incidence rates for 'any virus', we assumed children were at risk of being positive for new viruses in every swab.