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

There are also some important limitations to consider. To reduce the chances of false-negative test results, 21 we excluded from analysis 2679 (23.9%) swabs where the internal control for human DNA, ERV-3, was either undetected or present at very low levels. We excluded both virus-positive and virus-negative swabs to avoid overestimating our incidence and prevalence rates. In addition, some viruses were detected rarely, in particular influenza, a finding reflected in other community studies, 17 but nevertheless limiting our ability to provide precise AFE estimates for these agents. We also excluded codetections in individual virus assessments as multiple aetiological agents make individual contributions of each agent difficult to ascertain, but analysed them separately to look at the association patterns of individual viruses. Symptom information, other than doctor-diagnosed otitis media and pneumonia, captured by daily diaries was not validated. To maximise accuracy, parents were trained to recognise symptoms before commencing the study. While healthcare worker-validated symptoms would be ideal, a study of this scale is logistically challenging without parent participation. This study design has been used previously 18 and with others have shown that parents can be trained to recognise symptoms of interest, 18 often as reliably as healthcare professionals. 32 33 Our rates of ARI, including those associated with wheeze, are comparable with other community studies. 34 35 Finally, as is common for these types of studies, families in our cohort were from more advantaged backgrounds and ARI episodes were predominantly of a mild-to-moderate nature. 22 While many children in our study were first-born and from advantaged families, factors thought to decrease the rate of ARIs, secular changes in Australia have led to an increased proportion of children from these families attending childcare at an earlier age than other sectors of the population. A slightly higher proportion (80%-85%) of our cohort attended some form of care by the age of 15-24 months, compared with 74% of children in the Australian population, with childcare attendance an independent risk factor for ARIs. 25 Moreover, the incidence of ARIs in the ORChID cohort 22 is comparable to other reports in this age group 34 36 37 and RSV and HRV-associated ARIs approximate other community-based studies conducted in more temperate climates of Australia (Perth) and Europe. [38] [39] [40] Our findings for this cohort remain valid and provide important estimates on community respiratory virus exposures and ARIs in Australian children in a subtropical, urban setting.