Background: Indigenous children in Australia and Alaska have very high rates of chronic suppurative lung disease (CSLD)/
bronchiectasis. Antibiotics, including frequent or long-term azithromycin in Australia and short-term beta-lactam therapy in
both countries, are often prescribed to treat these patients. In the Bronchiectasis Observational Study we examined over
several years the nasopharyngeal carriage and antibiotic resistance of respiratory bacteria in these two PCV7-vaccinated
Methods: Indigenous children aged 0.5?8.9 years with CSLD/bronchiectasis from remote Australia (n = 79) and Alaska
(n = 41) were enrolled in a prospective cohort study during 2004?8. At scheduled study visits until 2010 antibiotic use in the
preceding 2-weeks was recorded and nasopharyngeal swabs collected for culture and antimicrobial susceptibility testing.
Analysis of respiratory bacterial carriage and antibiotic resistance was by baseline and final swabs, and total swabs by year.
Results: Streptococcus pneumoniae carriage changed little over time. In contrast, carriage of Haemophilus influenzae declined
and Staphylococcus aureus increased (from 0 in 2005?6 to 23 in 2010 in Alaskan children); these changes were associated
with increasing age. Moraxella catarrhalis carriage declined significantly in Australian, but not Alaskan, children (from 64 in
2004?6 to 11 in 2010). While beta-lactam antibiotic use was similar in the two cohorts, Australian children received more
azithromycin. Macrolide resistance was significantly higher in Australian compared to Alaskan children, while H. influenzae
beta-lactam resistance was higher in Alaskan children. Azithromycin use coincided significantly with reduced carriage of S.
pneumoniae, H. influenzae and M. catarrhalis, but increased carriage of S. aureus and macrolide-resistant strains of S.
pneumoniae and S. aureus (proportion of carriers and all swabs), in a `cumulative dose-response? relationship.