|Tuberculosis screening of travelers to higher-incidence countries: a cost-effectiveness analysis
|Tan M, Menzies D, Schwartzman K
This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn.
The objective was to assess the cost-effectiveness of four potential screening strategies for travellers from countries with low-incidence of tuberculosis travelling to countries with varying incidence of the disease. A single post-trip tuberculin skin test was the most cost-effective strategy but screening strategies were expensive from the perspective of the US and Canadian health care systems, except at high rates of disease incidence. The clinical analysis was not extensively described and caution is required when interpreting the authors’ conclusions.
Type of economic evaluation
The objective was to assess the cost-effectiveness of four potential screening strategies for travellers from countries with low-incidence of tuberculosis (TB) travelling to countries with varying incidence of disease (Mexico, Dominican Republic or Haiti). The populations considered were travellers born in the USA or Canada, and travellers residing in the USA or Canada but born in Mexico, the Dominican Republic, or Haiti, who travelled to their country of birth.
The strategies under examination were: post-trip tuberculin skin testing (TST), post-trip chest X-ray, pre- and post-trip TST with treatment for reactors, pre- and post-trip TST with treatment for converters only, and no screening.
USA and Canada/primary care.
This economic evaluation was based on a decision analytic model that determined the clinical and economic impact of the different strategies. The time horizon of the analysis was 20 years and the authors stated that the perspective of the health care system was adopted.
The clinical data were derived from a selection of known, relevant studies, but the methods used to identify these studies were not described. The incidences of TB in Mexico, Dominican Republic and Haiti were taken from local data, while the mortality from all causes and TB-related mortality were taken from Canadian and US life tables. The risk of transmission among contacts was taken from a published mathematical model. Disease progression was estimated on the basis of other published studies, the details of which were not provided. Some assumptions were also made.
Monetary benefit and utility valuations:
Measure of benefit:
The summary benefit measure was the rate of TB cases prevented and a 3% annual discount rate was applied.
The health service costs were initial clinic visit, tuberculin skin test, follow-up clinic visit after tuberculin test, chest radiograph (including reading), isoniazid (nine-month supply and treatment of adverse events), outpatient clinic visits, sputa for acid-fast bacilli smear and culture after abnormal chest radiograph, (inpatient and outpatient) treatment of active TB disease, contact investigation and management. The US costs were derived from two US surveys of TB-related health care costs as well as from the fee schedule published by the US Centers for Medicare and Medicaid Services. The Canadian costs were obtained from previous programme evaluations and cost-effectiveness analyses from Montreal. All the costs were in US dollars ($) and the price year was 2005. Discounting was relevant given the long-term horizon of the analysis and an annual rate of 3% was used.
Analysis of uncertainty:
A one-way sensitivity analysis was performed for all model inputs. The ranges of values tested appear to have been derived from published sources or from authors’ opinions. A two-way sensitivity analysis focused on simultaneously varying the visit duration and the annual risk of infection in the destination country.
In a cohort of 1,000 US-born 21 year old travellers spending three months in Mexico, with no screening as the reference strategy and after the exclusion of dominated strategies, the incremental cost per case prevented over no screening was $161,196 with post-trip TST. In a cohort of 1,000 Mexico-born travellers to Mexico, the incremental cost per case prevented over no screening was $143,578 with post-trip TST.
In US-born travellers to the Dominican Republic, with no screening as the reference strategy and after the exclusion of dominated strategies, the incremental cost per case prevented over no screening was $102,745 with post-trip TST. In Dominican-born travellers to the Dominican Republic, the incremental cost per case prevented over no screening was $65,264 with post-trip TST.
In US-born travellers to Haiti, with no screening as the reference strategy and after the exclusion of dominated strategies, the incremental cost per case prevented over no screening was $36,931 with post-trip TST. In Haitian-born travellers to Haiti, the incremental cost per case prevented was $40,585 with post-trip chest X-ray and $1,014 with post-trip TST.
For Canadian travellers, costs were different, but outcomes were similar in that the single post-trip TST was the preferred option, with similar incremental cost per case prevented compared with no screening.
The sensitivity analysis showed that, as expected, the cost-effectiveness of the screening strategies improved as the risk of infection increased, and with increasing length of stay abroad. In particular, for US-born individuals travelling to Haiti, post-trip TST became dominant for a two-year length of stay.
The authors concluded that a single post-trip tuberculin skin test was the most cost-effective strategy among the available screening strategies. However, even under favourable assumptions, screening strategies were expensive from the perspective of the US and Canadian health care systems, except at high incidence of disease (such as in Haiti).
The selection of the alternative strategies appears to have been appropriate. The authors did not consider a further strategy of screening by means of interferon-gamma release assays due to the high cost of this option. However, this strategy might be more relevant for travellers born in countries where the Bacillus Calmette-Guérin (BCG) vaccination is administered such as in many European countries.
The authors provided incomplete information on several aspects of the clinical analysis. First, the approach used to identify primary sources of data was not reported. Second, the types of studies used and their key characteristics (design, patient population, follow-up, types of interventions) were not described. Third, other potential issues of the analysis such as the heterogeneity of the sources of data and the problems related to mixing different datasets were not addressed. This lack of information limits the possibility of judging the validity of the clinical data. The benefit measure represents a natural outcome of the screening strategies, although it is not easily comparable with the benefits of other health care interventions. The authors stated that the TB-related mortality was initially considered to be a relevant outcome but it was abandoned because the rate was too low.
The categories of costs were consistent with the viewpoint of the analysis and costs were reported as individual items for most categories. The price year and the use of discounting were stated. However, the sources of data were not described in detail, especially with respect to the Canadian setting. Moreover, costs were only partially varied in sensitivity analyses, thus uncertainty around these values was not fully investigated.
Analysis and results:
The synthesis of costs and benefits was appropriately carried out. The issue of uncertainty was partially addressed by considering variations in some individual model inputs. The results of the most relevant sensitivity analyses were clearly reported. The authors acknowledged some limitations of the analysis such as the use of a restricted study perspective and the method used to estimate the annual risk of infection.
Although the study methodology appears to be sound and the results were clearly reported, the main sources for the analysis were not extensively described, especially for the clinical data. Thus, caution is required when interpreting the authors’ conclusions.
Supported by awards from the Fonds de la Recherche en Sante du Quebec.
Tan M, Menzies D, Schwartzman K. Tuberculosis screening of travelers to higher-incidence countries: a cost-effectiveness analysis. BMC Public Health 2008; 8: 201
Other publications of related interest
Schwartzman K, Menzies D. Tuberculosis screening of immigrants to low-prevalence countries. A cost-effectiveness analysis. Am J Respir Care Med 2000;161:780-9.
Schechter CB, Rose DN, Fahs MS et al. Tuberculin screening. Cost-effectiveness analysis of various testing schedules. Am J Prev Med 1990;6:167-75.
Dasgupta K, Schwartzman K, Marchand R et al. Comparison of cost-effectiveness of tuberculosis screening of close contacts and foreign-born populations. Am J Respir Crit Care Med 2000:162(6):2079-86.
Subject indexing assigned by NLM
Adult; Canada /epidemiology; Cost-Benefit Analysis; Decision Support Techniques; Disease Outbreaks /prevention & Dominican Republic; Haiti; Humans; Incidence; Markov Chains; Mass Chest X-Ray /economics /statistics & Mass Screening /economics /statistics & Mexico; Skin Tests /economics /statistics & Travel /statistics & Tuberculin Test; Tuberculosis, Pulmonary /epidemiology; United States /epidemiology; control; numerical data; numerical data; numerical data; numerical data
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