Pseudoepidemic of endocarditis in patients undergoing open heart surgery

Area of Science:

• Microbiology
• Clinical Pathology
• Surgical Pathology

Background:

• Gram staining of heart valve tissue is crucial for diagnosing endocarditis.
• Initial investigations identified gram-positive cocci in excised heart valve tissue from patients undergoing replacement surgery.
• Standard microbiological procedures at the time were insufficient for isolating strict anaerobes.

Purpose of the Study:

• To investigate the cause of false positive Gram stain results in heart valve tissue.
• To identify the source of contamination leading to misdiagnosis of bacterial endocarditis.
• To implement corrective measures to prevent future occurrences of false positive results.

Main Methods:

• Review of patient records for heart valve replacement surgeries within a specific period.
• Microscopic examination of excised heart valve tissue and Gram staining.
• Analysis of microbiological laboratory procedures, including media preparation and sample handling.
• Investigation of commercially prepared trypticase soy broth for contaminants.

Main Results:

• Four cases initially showed gram-positive cocci on Gram stain of heart valve tissue, but cultures were negative.
• Contamination was traced to nonviable, gram-positive cocci in commercially prepared trypticase soy broth.
• Visible sediment in the broth tubes was identified as the source of contamination.
• Revised broth handling and introduction of a screening procedure eliminated false positive results.

Conclusions:

• Commercially prepared microbiological media can be a source of contamination, leading to spurious diagnostic results.
• A simple screening procedure for microbiological broth effectively prevents false positive Gram stain findings in heart valve tissue.
• Accurate diagnosis of endocarditis requires careful attention to laboratory procedures and quality control of reagents.