Effects of seasonal, geographical and demographic factors on otitis externa microbiota in Queensland, Australia.

Background and objectives: Otitis externa (OE) is a very common disease in Australia. It is associated with swimming and exposure to water. Typically, treatment consists of aural toileting and the use of topical antimicrobial drops. Antimicrobial treatment is empiric, and most Australian guidelines advise the use of dexamethasone/framycetin/gramicidin as first-line therapy. This study aimed to identify the most prevalent pathogens implicated in OE in Queensland, Australia, and determine if there was any variability with the season, proximity to a coastline, age, gender and First Nations status.

Method: The primary pathogen cultured, the specimen type, the date of collection and the patient demographics were retrieved from microbiology swabs sent from hospitals to Pathology Queensland. Multivariate analysis was performed on the swabs.

Results: Pseudomonas aeruginosa was the most prevalent pathogen cultured in the external ear in Queensland, at 37.9%. In inland regions, Staphylococcus aureus was the most prevalent organism. Children were three-fold less likely to have OE resulting from a fungal pathogen.

Discussion: The use of targeted antimicrobials against Pseudomonas aeruginosa in coastal regions during summer is sensible. Due to the low burden of fungal disease in children, there should be a high threshold for the commencement of antifungal ear drops.