Conventional vs Rapid Molecular Diagnostic Strategies for M.tuberculosis (M.tb): A Cost-effectiveness Analysis (CEA).

J. CONLY*, S. KRAJDEN, M. KRAJDEN, R. BANNATYNE, W. WOBESER and THE TORONTO RAPID DIAGNOSTICS CONSORTIUM,

The Toronto Hospital, St. Joseph's Health Care Centre, St. Michael's Hospital, and The University of Toronto, Toronto, ON, Canada.

The resurgence of M.tb in conjunction with HIV and the appearance of multi-drug resistant strains has focused attention on the need for a rapid diagnostic strategy for M.tb. With the capability of polymerase chain reaction (PCR) to offer a high cost same day diagnosis we performed a CEA of 3 diagnostic strategies for M.tb. Following NAC-Na0H concentration of the specimen we compared 1) conventional - smear, Bactec^tm culture and NAP test 2) nucleic acid probe - Bactec^tm and Accuprobe^tm (GenProbe) and 3) PCR-Amplicor^tm (Roche) on smear positive vs both smear positive and negative specimens to determine the costs per isolation day prevented. With a smear sensitivity of 50%, 5 admissions/month with positive sputum smears, a 30% isolation rate of M other than M.tb, 17 days to the first positive culture, 5 days to a positive NAP, isolation costs of $945/5 days, and assuming a constant volume of tests/month, labour costs adjusted for batch size, no hospital contacts, and initial standard 4 drug regimen, 7 days in-hospital isolation, and 50% utilization of isolation rooms by third party payers we determined the total costs of isolation days and isolation days prevented for each of the strategies:

Strategy	Annual Cost	Isolation Days	Potential Savings
Conventional	$8,200	420	---
Accuprobetm	$8,700	420	---
Amplicortm (smear positve only)	$28,000	120	$162,000
Amplicortm (all)	$61,000	120	$162,000

Based on this model, the Amplicor^tm-PCR on only smear positive specimens was the most cost-effective diagnostic strategy. Varying the volume of tests done and the frequency of need for isolation can dramatically alter the costs per isolation day saved.