Assessing the Effect of “Time of Birth” on Nasopharyngeal Microbial Load in Infants

Acute otitis media (AOM) is one of the most common childhood infections and its pathogenesis involves complex interactions between bacteria and viruses. Bacteria and viruses contributing to the AOM are collectively known as otopathogens. The objective of the capstone is to assess the effect of “month of birth” (MOB) on the microbial load of the most abundant otopathogen, Moraxella Catarrhalis. This is a retrospective analysis of data collected between 2009 – 2014 as part of a longitudinal study to determine risk factors for AOM. Subjects were recruited near birth and followed up to 1 year of age. For measurement of nasopharyngeal microbial abundance, approximately seven specimens were taken per subject. The total number of patients and specimens in the dataset are 139 and 948 respectively. The outcome variable was the log-transformed relative abundance of Moraxella genera. Its relationship with MOB was modeled using generalized additive mixed effects models (GAMM) controlling for age, month of specimen collection and other covariates while blocking on subject to control for repeated measures. Model selection was based on Bayesian Information Criterion (BIC). MOB showed a statistically significant non-linear relationship with Moraxella microbial abundance (p < 0.001). Increasing age and birth order were positively associated with the outcome (p < 0.001 and p = 0.03 respectively). The effect of MOB displayed a cyclic seasonal nature. This finding suggests that the timing of birth affects the average Moraxella microbial abundance in the first year of life. Our data demonstrate that MOB can be used to identify high risk populations for AOM. Further investigation on the underlying mechanisms mediating this complex relationship may aid in broadening the clinical understanding of AOM disease process.