CLINICAL UTILITY OF CARDIAC-VALVE GRAM STAIN AND CULTURE IN PATIENTS UNDERGOING NATIVE VALVE-REPLACEMENT

Objectives.-To determine if routine cardiac valve culture is useful in diagnosing clinically unsuspected infective endocarditis in patients undergoing native valve replacement, to see if false-positive culture results have a deleterious effect on patient care, and to determine if microbiology and histopathology can be used to differentiate partiall y treated and untreated infective endocarditis from valve contaminatio n. Design.-Case series. Setting.-Tertiary-care teaching hospital with 1125 beds. Patients.-Forty-eight patients with culture-positive cardia c valves after native valve replacement. Results.-A single unsuspected case of endocarditis was disclosed by microbiology over a 5-year peri od. Histopathology in this case was also positive, however, and the di agnosis should have been suspected clinically. Eighty-three percent of positive cultures were the result of contamination over an 18-month p eriod; results were disregarded appropriately by clinicians. Clinical context or histopathology was required to categorize microorganisms co rrectly as pathogens or contaminants; only the presence of organisms o n Gram stain had a good predictive value for endocarditis. Conclusion. -Routine valve cultures in patients undergoing native valve replacemen t are not warranted. Although false-positive culture results had no de leterious effects on patient care in this study, misinterpretation of such results could lead to overtreatment. Microbiology results alone a re not sufficient to distinguish endocarditis from contamination.