Haemophilus parainfluenzae endocarditis in a patient with mitral valve prolapse.

Haemophilus parainfluenzae is a frequent cause of "culture-negative" endocarditis (i.e., endocarditis owing to a fastidious organism which may require longer incubation periods and/or enrichment media for detection compared to traditional pathogens). More cases will probably be identified with improvements in growth and isolation techniques. A case of H. parainfluenzae endocarditis is presented in a patient with mitral valve prolapse, which illustrates the difficulty in diagnosing endocarditis when initial blood cultures are negative. Particularly, it emphasizes the difficulty in selecting appropriate antibiotic therapy since beta-lactamase producing organisms are being isolated with increased frequency. This report is unique in that it documents successful treatment with a cephalosporin and what is, to our knowledge, the third reported case of a beta-lactamase producing H. parainfluenzae causing endocarditis. The authors believe that beta-lactamase stable second or third generation cephalosporins should constitute initial treatment of H. parainfluenzae endocarditis until sensitivity studies become available, since beta-lactamase production by this organism would nullify the effect of the previous agent of choice, ampicillin.