Pseudoepidemic of endocarditis in patients undergoing open heart surgery.

Between July 2 and July 16, 1979, three patients were reported to have gram-positive cocci as seen on Gram strain of excised, macerated heart valve tissue. No organisms were isolated in culture; however, our usual procedure for handling such valves is not adequate for isolation of strict anaerobes. The first patient was treated for presumed endocarditis; this resulted in three additional weeks of hospitalization. Review of the remaining 34 patients who had heart valve replacement surgery between February 1 and July 20, 1979 revealed three additional cases. Careful analysis revealed that nonviable, gram-positive cocci present in commercially prepared trypticase soy broth were being added to the tissue just prior to mortar and pestle grinding in the microbiology laboratory. The contaminated tubes were noted to have a visible sediment when carefully examined. The procedure for handling the broth has been revised; a simple screening procedure is used now to identify potentially contaminated broth. No further instances of false positive results on Gram-staining of heart valve tissue have occurred since this screening procedure was introduced.