Molecular and epidemiological analysis of methicillin-resistant Staphylococcus aureus otorrhoea: hospital- or community-acquired?

OBJECTIVES: (1) To identify newly diagnosed cases of methicillin-resistant Staphylococcus aureus ear infection in our local population; (2) to determine the risk factors involved in these patients' clinical courses, and (3) to type the bacterial strains isolated and thus identify whether they were hospital- or community-acquired.

DESIGN AND SETTING: Retrospective review of case notes, together with laboratory-based molecular studies in the departments of otolaryngology and medical microbiology in a university teaching hospital in Scotland, UK.

SUBJECTS: Over a two-year period, 35 patients were identified with ear swabs positive for methicillin-resistant Staphylococcus aureus infection. These cases came from both hospital and community settings.

MAIN OUTCOME MEASURES: (1) Identification of primary methicillin-resistant Staphylococcus aureus otorrhoea in patients with no previously documented colonisation; and (2) molecular typing of the strains isolated, using spa technology, to identify whether they were hospital- or community-acquired.

RESULTS: Of the 35 positive patients, 27 were previously known carriers of methicillin-resistant Staphylococcus aureus. The eight patients with newly diagnosed methicillin-resistant Staphylococcus aureus otorrhoea presented initially in the community. All of these patients had had contact with hospital staff (as in-patients or out-patients) in the weeks preceding development of their ear infection. Using the spa technique for molecular typing, we identified hospital-acquired ('epidemic') methicillin-resistant Staphylococcus aureus type 15 in all eight patients' isolates. All were sensitive to topical gentamicin.

CONCLUSIONS: In our cohort, hospital-acquired methicillin-resistant Staphylococcus aureus type 15 was the commonest cause of methicillin-resistant Staphylococcus aureus otorrhoea, despite the fact that these patients all first presented in the community. We believe that contact with hospital staff or health care workers is a risk factor for acquiring methicillin-resistant Staphylococcus aureus otorrhoea in the community.