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Fig. 2. Probabilistic sensitivity analysis on cost effectiveness of
“no screening,”“new
international þ triennial high-risk,”“new þ tri- ennial universal,”“new þ triennial universal þ annual high-risk,” and “newþannual universal” screening strategies.
Annual universal screening for all employees (“new þ annual universal”) was the least cost-effective (US$26,646 per TB case
averted; US$311/QALY). Screening new hires alone (“new”) was more costly and less effective than screening only new international employees and high-risk workers once (“new
international þ triennial high-risk”), and screening of new international hires combined with annual high-risk screening
(“new international þ annual high risk”) was also more costly and less effective than screening all newly employed and existing
employees once (“new þ triennial universal”). These 2 strategies (“new” and “new internationalþannual high risk”) were therefore considered dominated and were removed from further analyses.
The base case 3-year total budget for TB control under “no
screening” was US$238,379, which is the cost of diagnosing and managing active TB cases. Under the most cost-effective strategy
of “new international þ triennial high risk,” the total hospital budget would be US$332,571, or an additional US$95,000 over 3 years. To decrease the overall cost, the cost of QFT-G (which accounted for majority of the budget in all strategies) could be tar- geted for reduction. The one-way sensitivity analysis for undominated screening
strategies relative to “no screening” (Fig. 1) shows that ICERs are most sensitive to the cost of QFT-G. However, since all the ranges of recalculated ICER values fall well below US$50,000 per QALY, our cost-effectiveness findings are robust (ie, our con- clusions remained unchanged across a realistic range of possible parameters). One-way sensitivity analysis on the BIA results (Supplemental Material Fig. 2 online) showed that in general, the budget would be most sensitive to changes in the total number of HCWs and the retention rate. Finally, the CEAC (Fig. 2) showed that at lower willingness-to-
pay thresholds, the targeted screening strategy is most likely to be cost-effective. However, if willingness-to-pay is sufficiently high, a policy of universal screening can most likely be cost-effective.
Discussion
Nosocomial TB exposures are inevitable in moderate to high-TB- burden countries where screening of LTBI in HCWs is not rou- tinely practiced. Policy makers contemplating a LTBI screening
program for HCWs need to consider trade-offs among the addi- tional number of active TB cases prevented, resources used, and budget limitations. A risk-stratified approach to LTBI screening in HCWs may be a novel, pragmatic, and cost-effective strategy, especially in countries like Singapore, where a large proportion of HCWs originate from high TB-burden countries.9 Although regular universal screening can be most effective, it is
most expensive and likely to be cost-effective only at high levels of willingness-to-pay. The total cost of instituting universal LTBI screening for all new and existing HCWs is $26,646 per active TB case averted, and policy makers would need to decide its worth. Our results showed that in this setting, targeted screening is likely to be highly cost-effective. The most cost-effective approach in our model involved screening of all new HCWs from high-risk coun- tries of origin, and triennial screening every 3 years for existing HCWs in high-risk clinical areas, costing $6,745 per active TB cases averted (reducing active TB cases from 19 to 14). Our con- clusions differ from a recent study published by Mullie et al,27 pos- sibly because that analysis was conducted with relatively high frequency screening in a low-incidence TB country from the healthcare system perspective. Ultimately, decision makers need to weigh the inevitable trade-
off of greater cost-effectiveness against the greater risk of missed cases. On the one hand, missed TB cases can have heavy clinical, legal, and financial consequences for a healthcare system28 particu- larly because whole-genome sequencing has enabled more precise tracing of index cases in outbreak scenarios.29 On the other hand, screening of existing employees in high-risk clinical areas requires additional resources to ensure adherence to LTBI testing and treat- ment, and resource constraints may be binding or systemic prior- ities may lie elsewhere. Wherever possible, decision makers should also consider the use
of innovative strategies to increase the efficiency of screening itself. To improve adherence, LTBI screening could be added to existing routine pre-employment screening (ie, screening for hepatitis B, verifying immunity to varicella and measles) and implementing a system to ensure regular LTBI screening for existing workers. Finally, our results are most sensitive to the cost of QFT-G,
which is the most expensive item. Reducing the cost of QFT-G could make all screening strategies more cost-effective, and even
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