A RISK COST ANALYSIS OF ALTERNATIVE SCREENING INTERVALS FOR OCCUPATIONAL TUBERCULOSIS INFECTION/

The Centers for Disease Control and Prevention (CDC) recommends that n ew health care employees receive a baseline skin test for Mycobacteriu m tuberculosis (M. tb) infection and that testing be repeated periodic ally. However, CDC does not explain the quantitative basis for its sug gested screening intervals. This article examines the efficacy of alte rnative screening intervals for workers subject to different annual ra tes of M. tb infection and estimates the costs. An equation is develop ed for the cumulative risk of tuberculosis (TB) at 12 years given a sp ecified annual rate of infection (ARI), screening interval, and a comb ined proportion (p) of successful skin testing and antibiotic prophyla xis. Equations for total cost of screening and cost per disease case p revented a re provided. Results assume: (a) costs of $10 per skin test and $10,000 per TB disease case; (b) p = 0.88; and (c) an acceptable cumulative TB risk of 1 per 1000. For ARIs that might be deemed low (0 .2% to 0.5%) and medium (1%), CDC screening intervals of 12 months and 6-12 months, respectively, minimize the cost per disease case prevent ed but permit residual disease risks greater than 1 per 1000. Recommen ded screening intervals are (i) 6 months for low-risk employee groups and (ii) 3 months for medium- and high-risk (e.g., ARIs of greater tha n or equal to 5%) groups. Interval (i) limits risk to 1 per 1000 and i s approximately 50% shorter than the CDC interval for a low-risk group . interval (ii),which is 67% shorter than the CDC interval for medium- risk groups but equal to that recommended for high-risk groups, permit s a risk above 1 per 1000, but is likely the shortest feasible interva l.