Otitis externa following aural irrigation linked to instruments contaminated with Pseudomonas aeruginosa

Summary

Background

The incidence of acute otitis externa, an infection of the external auditory canal, in general practitioners’ (GP) practices in The Netherlands is about 14 per 1000 patients per year. In early 2010, one of the authors noted that some of the otitis externa patients in his GP practice had undergone cerumen removal by ear syringing a few weeks earlier. Bacterial cultures of samples taken from the instruments used showed contamination of an ear syringe by Pseudomonas aeruginosa. From then on, P. aeruginosa isolates from patients' ears were stored in the laboratory.

Aim

It was assessed whether cross-contamination with P. aeruginosa between patients in the same GP practice could occur through the use of contaminated ear lavage instruments.

Methods

From 17 GP practices, the otolaryngology Outpatient Department and the Out-of-Hours GP Service, instruments used for examining and cleaning the outer ear were swabbed. Strains of P. aeruginosa cultured from the instruments were genotyped together with isolates of patients registered in the same practice.

Findings

In four practices where contaminated instruments were found, genotyping showed similarity between P. aeruginosa strains isolated from a patient and the ear syringe, and/or between strains of different patients in the same practice.

Conclusions

Transmission of P. aeruginosa from ear lavage instruments to patients appears to occur with otitis externa as a result. Together with the Infection Control Unit of our hospital we have formulated recommendations for the appropriate cleaning, disinfection and storage of re-usable ear lavage instruments for the GP practices to implement.

Introduction

Otitis externa is an infection of the external auditory canal. Ear wax (cerumen) produced by glands in the skin of the auditory canal normally has a pH value of 5.0, giving it a bactericidal effect.1, 2 The lack of protection by cerumen and/or the intact skin increases the chances of acquiring otitis externa.³ In general practitioners' (GP) practices in The Netherlands, each year about 14 per 1000 patients are diagnosed with an acute otitis externa.⁴ Often Pseudomonas aeruginosa is found as the causative agent.⁵ In January 2010, one of the authors noted that some of the otitis externa patients in his GP practice had undergone cerumen removal by ear syringing (lavage) a few weeks earlier. In all cases P. aeruginosa had caused the infection. In consultation with the Laboratory of Clinical Microbiology and Infectious Diseases (LMMI) of the Isala klinieken in Zwolle, The Netherlands, he took swabs from the instruments used for ear syringing. Bacterial cultures showed that the instruments were contaminated with P. aeruginosa. This raised the question whether cross-contamination with P. aeruginosa between patients belonging to the same GP practice could occur through the use of contaminated ear lavage instruments (proof of principle). The question was explored in this molecular epidemiological study in a number of GP practices. Our null hypothesis was that we would not encounter any epidemiological relationship by molecular testing of the P. aeruginosa strains isolated from the patients with otitis externa.