Perform or perish: Laboratory optimization to avoid false negative blood cultures in pneumococcal bacteremia

We present the laboratory operations influencing the culture yield of pneumococci and suggest an alternate solution to the problem. Blood cultures of 136 adults and 19 pediatric patients were analyzed in two phases. In phase I, the laboratory operated only during weekdays but in phase II the laboratory provided 24-h services on all days. In phase I, successful bacterial isolation leading to testing of antimicrobial susceptibility was possible only in 51% of cases, while a significant 49% had failed to grow in subcultures due to autolysis resulting from delayed processing time. These false negative blood cultures were further confirmed as Streptococcus pneumoniae by commercial antigen tests. In phase II, we did not observe any false-negative results due to prompt subculturing protocols (p < 0.001). We also found that taking blood cultures on two occasions increases the yield by 46% among adults.