Haemophilus parainfluenzae mitral prosthetic valve endocarditis in an intravenous drug abuser.

Haemophilus species are an infrequent cause of subacute bacterial endocarditis. Of the Haemophilus species causing endocarditis, H. aphrophilus and H. parainfluenzae are more frequent causes of subacute bacterial endocarditis than H. influenzae. H. parainfluenzae requires growth factor V (nicotinamide adenine dinucleotide) and grows very slowly on routine culture media. H. parainfluenzae is a rare cause of "culture negative" endocarditis because it is a slow-growing organism. We present a case of a 42-year-old intravenous drug abuser with H. parainfluenzae mitral prosthetic valve endocarditis. To the best of our knowledge, this is the first case of mitral prosthetic valve endocarditis caused by H. parainfluenzae in an intravenous drug abuser.