Ampicillin-Resistant Strains of Hemophilus influenzae type B

Abstract

Strains of Hemophilus influenzae type b highly resistant in vitro to ampicillin have been reported from several widely separated locations in the United States since December 1973.1-4 These strains were isolated from children with meningitis and the clinical course corroborated the in vitro susceptibility results. Until the importance of these resistant strains can be ascertained, hospital laboratories are urged to test clinical isolates of H. influenzae type b for susceptibility to ampicillin, and physicians must reconsider the treatment of patients with severe disease due to this organism. Ampicillin disk sensitivity tests of H. influenzae isolates are satisfactory for screening purposes but strains that are of equivocal sensitivity or are resistant should also be tested by a quantitative method, such as the tube dilution or agar diffusion techniques. The appropriate methods for antibiotic susceptibility tests were reviewed recently in a weekly report of the Center for Disease control.5 If facilities for these tests are unavailable or if confirmation of test results is desired, the bacterial strains may be forwarded, via the State Public Health Laboratory, to the Center for Disease Control. In areas where resistant strains have been recognized, initial therapy of children with documented or suspected severe infection due to H. infiuenzae type b, such as sepsis, meningitis, epiglottitis, arthritis, or cellulitis, should include an antimicrobial agent of known efficacy. Initial administration of penicillin G or ampicillin and chloramphenicol would seem appropriate at this time. The antimicrobial regimen should be reevaluated when the results of the bacterial isolation studies and antimicrobial sensitivity tests are available.