Incidence of ampicillin-resistant Hemophilus influenzae in otitis media.

Ampicillin resistance in Hemophilus influenzae type b causing serious infections is appreciated, but little is known about ampicillin resistance in nonencapsulated strains causing otitis media. The ampicillin sensitivity of 984 middle-ear isolates of H. influenzae from children in Huntsville, Ala. obtained from 1970-1976, was examined: Nine AmpR isolates were found: one in 1973, two in 1974, three in 1975, and three in the first five months of 1976. Seven strains were nonencapsulated; two were type b. All nine produced beta-lactomase. The incidence of ampicillin resistance in strains causing otitis media increased from 0.6% in 1973 to 2.4% in 1976. AmpR H. influenzae infection should be suspected in situations where ampicillin therapy of otitis media is unsuccessful.