Haemophilus parainfluenzae and influenzae endocarditis: a review of forty cases

Two cases of bacterial endocarditis caused by Haemophilus parainfluenzae are reported with a review of 33 other cases of H. parainfluenzae endocarditis and 5 cases of H. influenzae endocarditis. Although H. parainfluenzae is usually considered a non-pathogenic microorganism, this review firmly establishes its role as a causative agent in endocarditis. Furthermore, several clinical features were noted which were atypical when compared to findings usually present in patients with bacterial endocarditis. The mean age of the patients was only 27 years. Over 60% of the patients had no identifiable predisposing illness, an unexpected finding in view of the low degree of pathogenicity associated with this microorganism. Polymicrobial bacteremia, usually with viridans streptococci, was found in 11% of patients. Major arterial emboli were documented in 57% of patients, an incidence unchanged from the pre-antibiotic era. Diagnosis of the disease is dependent upon an awareness of the fastidious cultural requirements necessary for isolation of Haemophilus species. Culture media must contain a source of X and V factors. Mortality from H. parainfluenzae endocarditis has been reduced from 100 per cent prior to 1940 to about 12 per cent by use of appropriate antimicrobial agents. Awareness that Haemophilus species can cause bacterial endocarditis is important because the diagnosis is dependent upon utilization of special culture methods and the patient may not respond to some of the empiric regimens used for treating bacterial endocarditis. It should be especially considered as a possible cause of "culture-negative" or "abacteremic" endocarditis.