Prevalence and determinants of antibiotic exposure in infants: A population-derived Australian birth cohort study

Aim: The aim of this study was to describe antibiotic exposure in Australian infants during the first year of life, focusing on antibiotic class, indication, risk factors associated with exposure and comparison with international counterparts. Methods: The Barwon Infant Study is a birth cohort study (n=1074) with an unselected antenatal sampling frame from a large regional centre in Victoria, Australia. Longitudinal data on infection and medication were collected at 1, 3, 6, 9 and 12 months by parental questionnaire and from general practitioner and hospital records. Predictors of questionnaire non-completion were identified. A total of 660 infants with complete serial data were comprehensively examined. Antibiotic exposure was calculated as (i) antibiotic prescriptions and (ii) antibiotic days-exposed per person-year. Results: Mean antibiotic prescription rate was 0.92 prescriptions (95% confidence interval (CI), 0.83-1.02) per person-year, with the highest rates in those aged <1month (1.50 (95% CI, 1.09-1.91) per person-year). A total of 50.0% of infants were exposed to at least one antibiotic in their first year of life. Increasing number of siblings was associated with increased antibiotic exposure. Penicillin with extended spectrum (365 of 661 antibiotic prescriptions, 52.6%) and cephalosporins (12.0%) were the most frequently prescribed antibiotics. One fifth of antibiotics were prescribed for respiratory tract infections and bronchiolitis. Conclusion: Australian infants in this large population-based study are exposed to considerably more antibiotics than the majority of their international counterparts. Interventions aimed at addressing avoidable prescribing by medical practitioners and modifiable risk factors associated with antibiotic exposure may reduce antibiotic use.