Microbial aetiology of otitis externa

Microbiological samples were collected from the ears of patients with otitis externa for a period of 1 year. Altogether, 226 evaluable samples from 104 males and 122 females were received. The age range of the patients was similar to that of the Norwegian population. A wide variety of bacteria and fungi was isolated. The commonest isolates, excluding normal flora, were Staphylococcus aureus (34.1%), Pseudomonas aeruginosa (22.1%) and Streptococcus pyogenes (8.8%); 9.3% samples contained fungi. Of all samples, 15% showed a mixture of Gram-positive and Gram-negative, potentially pathogenic, bacteria. Infection due to Gram-negative organisms alone was commoner in males, while the lack of any obvious microbial aetiology was more frequent in females. Isolation of S. aureus together with S. pyogenes was common but that of S. aureus together with S. pyogenes was common but that of S. aureus together with P. aeruginosa was unusual. In treated patients, the finding of streptococci and S. aureus was rare whereas that of P. aeruginosa or absence of growth was common. Otitis externa involving Gram-positive bacteria seems to be more prevalent in our area than in that of other reported studies.