Microbiology and antimicrobial treatment of otitis media.

Appropriate choice of antimicrobial agents for therapy of otitis media (OM) is based on an understanding of the microbiology of the acute and chronic diseases. The results of studies of bacteriology of OM are very similar: Streptococcus pneumoniae and Hemophilus influenzae are the most important pathogens; Gram-negative enteric bacilli are isolated from middle ear fluids (MEF) of approximately 20% of infants to 6 weeks of age; group A beta-hemolytic Streptococcus and Staphylococcus aureus are infrequent causes of otitis. Preliminary results suggest that anaerobic bacteria are responsible for some episodes of OM. Viruses and mycoplasma are infrequently isolated from MEF but Chlamydia trachomatis appears to be a significant cause of OM in young infants. Recent studies of asymptomatic children with persistent MEF indicate that bacterial pathogens are present in some of these fluids. The significance of these results is uncertain, but they suggest that the persistent effusion may be a result of prolonged infection or may be an immune response to bacterial antigens. Based on the bacteriology, amoxicillin or ampicillin are the currently preferred drugs for initial treatment of otitis media. For the child who is allergic to penicillins, cefaclor or erythromycin combined with a sulfonamide or trimethoprim-sulfamethoxazole are satisfactory alternatives. The current incidence of ampicillin-resistant H influenzae responsible for OM is low but if the patient does not respond to initial therapy with ampicillin or amoxicillin, infection with a resistant strain of H influenzae should be considered and a change in therapy to include a sulfonamide, trimethoprim-sulfamethoxazole or cefaclor is appropriate.