Diphtheroid endocarditis. Report of nine cases and review of the literature.

Diphtheroid endocarditis is a rare disease. A large proportion of the reported cases have occurred in the presence of prosthetic heart valves. Nine previously unreported cases of diphtheroid endocarditis are discussed along with 25 others taken from the literature. Eight out of the nine new cases occurred in patients with artificial heart valves. A high mortality was associated with infections occurring on prosthetic heart valves. Microbiological studies were frequently hampered by poor in vitro growth of the organisms. Resistance to penicillin and cephalothin was common. Erythromycin or penicillin in combination with streptomycin is suggested as a rational initial treatment for diphtheroid endocarditis involving prosthetic heart valves to be used until adequate in vitro antibiotic susceptibility testing is completed. Long-term suppressive therapy is suggested for those patients who are poor surgical candidates and for those patients who relapse after a reasonable course of antibiotic therapy.