Direct real-time PCR examination for Mycobacterium tuberculosis in respiratory samples can be cost effective

Aim: To assess whether the use of direct realtime polymerase chain reaction (PCR) on smear-positive sputa can be cost-effective, by speciating mycobacteria earlier than current methods and thereby preventing unnecessary screening tests as part of the contact tracing process. Methods: A retrospective study of all patients with smear-positive sputa in a Liverpool teaching hospital between 2004 and 2007. All the PCRs performed on these patients were reviewed and compared them with their mycobacterial culture results. Unit costs for PCR, chest X-ray (CXR), tuberculin skin test (TST), interferon-gamma (IFN-γ) and medical/nursing time were conservatively estimated at £50, £11, £10, £40 and £30 respectively. The total PCR costs were compared with the costs of unnecessary follow up of patients, negative for Mycobacterium tuberculosis (MTB) by PCR, subsequently confirmed to be MTB culture negative. Results: 203 smear-positive patients underwent direct PCR testing. 126 (62%) patients grew Mycobacterium tuberculosis (MTB), 74 (37%) had environmental mycobacterial infection (EMI) and 3 (1%) were culture negative. Of the 126 patients’ culture positive MTB patients, 123 were PCR positive and 3 PCR negative. Of the 77 patients that were culture negative for MTB, 75 were PCR negative and 2 PCR positive The sensitivity, specificity, positive and negative predictive values for direct PCR versus MTB culture were 98%, 96%, 98% and 97% respectively. Total costs of all PCRs performed amounted to £10,150. The cost of contact procedures for PCR-negative and MTB culturenegative index cases was estimated at £19,650. This equated to a total saving of £9,500 in contact tracing costs. Conclusions: Direct PCR examination testing of smear-positive patients can be cost-effective in areas where there is a high incidence of EMI.