The Epidemiology of Infectious Disease in the Growing Up in New Zealand Cohort Study

Abstract

Aim: New Zealand children suffer from high rates of infectious disease (ID) in general, and of skin and soft tissue infections (SSTI) in particular. Māori and Pacific children, and children in the most socioeconomically deprived households, are the most severely affected. This thesis sought to measure these ethnic and socioeconomic disparities, and determine the contribution of host, environmental and pathogen factors to the epidemiology of infectious disease in children enrolled in the Growing Up in New Zealand cohort study. Methods: Linkage was established between data obtained from interviews with the primary caregivers of cohort children, national administrative health datasets, and the results of bacterial cultures from the nose, throat and skin of cohort children, including genotyping results from isolates of Staphylococcus aureus and Streptococcus pyogenes. Unadjusted and multivariable regression adjusted associations between infection outcomes and explanatory variables were determined. Findings: Cohort children received a median of 8 antibiotic prescriptions dispensed by the age of five years, with Māori and Pacific children receiving a median of 9 and 11 courses respectively, and children living in the most deprived areas receiving a median of 9 courses. Hospitalisations for an infectious disease affected 25.6% of cohort children. Māori and Pacific ethnicity and reduced access to primary healthcare were associated with an increased risk of having had a hospitalisation for an ID. Māori and Pacific children were also disproportionately affected by community-onset SSTI. When considered independently, S. aureus and S. pyogenes colonisation were both associated with an increased risk of SSTI. However, when co-colonisation with both organisms was accounted for, colonisation with either organism alone was no longer associated with an increased risk of SSTI. Within the subset of children colonised with S. aureus, the genotype of S. aureus they were colonised with did not appear to affect the risk of SSTI, however, colonisation with a methicillinresistant strain or with multiple strains increased the risk. Conclusions: Māori or Pacific ethnicity and socioeconomic deprivation were associated with an increased risk across a broad range of ID-related health outcomes. These associations were only partly explained by the measured host, environmental, and bacterial factors. The remaining associations may be due to residual confounding and unmeasured factors.