Changes in antimicrobial resistance in acute otitis media and otitis externa.

Objectives: Acute otitis media (AOM) and otitis externa (OE) are common ear infections which may warrant antibiotic therapy. For many infections, there is a rise in antimicrobial resistance, which is associated with treatment failure, morbidity, prolonged hospitalisation and mortality. This study aimed to identify longitudinal changes in microbiology and antimicrobial resistance in aural swabs taken from patients with AOM or OE.

Design: Retrospective observational analysis.

Setting: Aural samples processed at Manchester Medical Microbiology Partnership Laboratories between January 2008 and December 2018 were analysed to record organism isolated and antimicrobial sensitivity.

Participants: Individual aural swabs from 7200 patients.

Main Outcome Measures: Changes in the incidence of organisms and antimicrobial resistance between two time periods (2008-2012 and 2013-2018) were compared using the chi-squared test (alpha = 0.05).

Results: From 7200 swabs, 2879 (40%) were from children. The most frequently isolated organisms were Staphylococcus aureus (25%), Pseudomonas aeruginosa (24.4%), yeast (9.1%), mixed anaerobes (7.9%) and Haemophilus influenzae (6.1%). In children aged 0-4 years, H. influenzae had particularly high incidence (25%). Overall, the incidence of P. aeruginosa decreased significantly with time (p = 0.05). Isolates displaying resistance to one or more antimicrobial agents increased significantly in number in the second time period for P. aeruginosa (p = 0.04) and H. influenzae (p =  0.03). There was increased resistance to amoxicillin for P. aeruginosa (p = 0.01) and to erythromycin for H. influenzae (p < 0.01).

Conclusion: Variations in type and frequency of organisms with increasing age likely result from differences in the preponderance of AOM compared to OE in children versus adults. We found increasing antimicrobial resistance for two organisms commonly isolated from AOM and OE infections, suggesting that aspects of current UK treatment practices and national recommendations may need to be revised.