Seven-pathogen tricuspid endocarditis in an intravenous drug abuser. Pitfalls in laboratory diagnosis. Polymicrobial endocarditis is being reported with increasing frequency in drug abusers. However, the full extent of infection may be unrecognized with routine blood culture techniques because of the overgrowth of more fastidious organisms by other pathogens. This report documents an intravenous drug abuser with the first reported case of tricuspid valve endocarditis involving seven pathogens, discusses pitfalls of routine blood cultures and examines the role of the laboratory in microbiologic diagnosis. 