Evaluation of the practice of routine culturing of native valves during valve replacement surgery

Background. We routinely cultured native heart valves removed during valve replacement surgery even when infected carditis (IE) was not suspected. Several probable contaminated cultures prompted us to evaluate this practice. Methods. The medical records of all patients who had positive valve cultures from 1995 to 1997 were reviewed for admission diagnoses, operative surgery, pathology and microbiology report, postoperative infections, and antibiotic use. Cases were excluded only for incomplete medical records or preoperative suspicion of IE. Long-term outcome for the cases was obtained from review of outpatient records and phone contact with the patient or physician. Results. Thirty-two of 222 (14.4%) evaluable patients had positive valve cultures. Coagulase-negative Staphylococcus was the most common isolate. IE was not suggested in any of these cases based upon the surgical or the pathology report. Only 1 of 32 (3%) developed postoperative prosthetic valve endocarditis (PVE). Three patients died of unrelated causes, and the 28 surviving patients showed no sign of PVE, with a mean follow-up of 23 months. Conclusions. The incidence of false-positive native valve cultures is high. Positive cultures did not predict the occurrence of PVE sufficiently to justify obtaining them. Treating patients who had positive native valve cultures would have been unwarranted and poses an unnecessary risk.