Introduction: Wearing hearing aid earmoulds has been implicated as a predisposing factor in the development of chronic otitis externa. Audiologists come into contact with a large number of hearing aid earmoulds and these could potentially harbour pathogenic micro-organisms, with the risk of subsequent cross infection. Cleaning with dilute alcohol is widely used in an attempt to break the chain of infection.

Objective: To determine the presence and nature of microbial flora on hearing aid earmoulds and the efficacy of cleaning methods used to prevent cross infection.

Setting: Secondary health care within the audiology department of Addenbrooke's Hospital, Cambridge, UK.

Design: A prospective, observational study.

Methods: Hearing aid earmoulds were swabbed before and after cleaning. Samples were cultured to determine qualitatively and quantitatively the microbiological flora present before and after cleaning.

Results: Twenty out of 21 (95 per cent) earmoulds had microbes present and, of these, 19/20 (95 per cent) had a polymicrobial profile. Coagulase negative staphylococci and diphtheroids were the most frequent microbial isolates, but pathogenic bacteria and fungi were also demonstrated on earmoulds both before and after cleaning.

Conclusions: The polymicrobial flora, including recognized pathogens, that colonizes earmoulds may lead to chronic otitis externa. Cleaning with 70 per cent alcohol solution was ineffective, in particular for pathogenic fungi on earmoulds.