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Cost-effectiveness of directly observed chemoprophylaxis of tuberculosis among drug users at high risk for tuberculosis |
Gourevitch M N, Alcabes P, Wasserman W C, Arno P S |
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Record Status 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. Health technology Direct observation of patients in order to improve compliance with therapy. In this case the example used chemoprophylaxis, specifically isoniazid (INH) for the prevention of tuberculosis, a regimen whose effectiveness depends heavily on patient compliance.
Economic study type Cost-effectiveness analysis.
Study population Current or former drug users, with or without HIV infection, in an inner city methadone maintenance programme who do not have active tuberculosis (TB).
Setting Specialist community drug treatment unit. The economic analysis was conducted in New York City, USA.
Dates to which data relate Effectiveness data on the incidence of TB were collected from literature published between 1989 and 1994. Resource data were collected between May 1995 and April 1996 and also from a 1993 publication. 1996 prices were used.
Source of effectiveness data Effectiveness data were taken from a review of previously published studies
Modelling A 5 year simulation model was created to estimate the number of cases of TB that would have been expected without the use of directly observed preventative treatment. Data for this model were taken from published literature on the prevalence, incidence and mortality associated with TB in drug users as well as the general population.
Outcomes assessed in the review Studies reporting incidence and mortality rates of TB and also risk rates for drug users and HIV positive patients of developing TB were identified.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included At least 6 studies were included in the review although the study types were not clearly reported.
Methods of combining primary studies Investigation of differences between primary studies Results of the review Probabilities of developing active tuberculosis were estimated.
New (recent (within last 2 years) tuberculin test conversion) HIV negative patients with positive PPD skin test result (for tuberculin reaction):
Year 1, 0.02;
Year 2, 0.01;
Year 3, 0.005;
Year 4, 0.005;
Year 5, 0.005.
Old (chronic, i.e. 2 or more years of reactive tuberculin test) HIV negative patients with positive PPD skin test result (for tuberculin reaction):
Year 1, 0.005;
Year 2, 0.005;
Year 3, 0.005;
Year 4, 0.005;
Year 5, 0.005.
New HIV positive patients with positive PPD skin test result (for tuberculin reaction):
Year 1, 0.2;
Year 2, 0.1;
Year 3, 0.09;
Year 4, 0.08;
Year 5, 0.07.
Old HIV positive patients with positive PPD skin test result (for tuberculin reaction):
Year 1, 0.07;
Year 2, 0.07;
Year 3, 0.07;
Year 4, 0.07;
Year 5, 0.07.
For HIV positive anergic patients these probabilities were 0.03 for all five years.
Measure of benefits used in the economic analysis The benefit measure was TB cases prevented.
Direct costs Costs associated with screening and identifying active TB in drug users, chemoprophylaxis, monitoring for toxicity, administration and staff costs for direct observation and costs of treating tuberculosis were estimated. Costs of screening and chemoprophylaxis were obtained from patient records at the study institution. Time spent by staff in administration, screening and monitoring of patients was determined by interviews with staff and by observation. It was assumed that costs would include treatment for a limited number of patients who would experience IHN-related hepatotoxicity. The costs of treatment for tuberculosis were taken from a previously published 1993 study on the economic impact of TB in New York. The authors considered the use of discounting but decided against employing it in the analysis. 1996 prices were used. The analysis was conducted from the perspective of a third party payer for the drug treatment unit programme.
Sensitivity analysis A number of parameters were varied in sensitivity analysis to deal with uncertainty in the model. These parameters included the effectiveness of INH chemoprophylaxis, HIV prevalence, probability of developing TB, and adding additional out-patient and multi-drug resistant costs.
Estimated benefits used in the economic analysis In the base case scenario with 65% overall effectiveness of INH treatment, 11 cases of TB would be avoided during the 5 year modelling period.
Cost results For a cohort of 507 patients registered on a drug treatment maintenance programme, the five year costs averted due to preventing 11 cases of TB were $398,295 or $785.59 per person. Overall net costs averted as a result of the programme were reported to be $285,284 or $563 per person. Thus the costs of screening for TB, and enrolling patients on a chemoprophylaxis programme under direct observation would appear to be $113,011, or $222.90 per patient.
Synthesis of costs and benefits In the base case scenario the average cost per case of TB averted using direct observation would be $10,274. The results of the analysis did not vary greatly under sensitivity analysis.
Authors' conclusions Direct observation of chemoprophylaxis for groups at high risk of developing tuberculosis such as drug users is highly cost effective.
CRD COMMENTARY - Selection of comparators A justification is provided for the comparator used, as this is a scenario without the use of chemoprophylaxis, the "do nothing option".
Validity of estimate of measure of benefit Probabilities for the development of TB among the target population were identified from a review of the literature. However, the methods used to identify the literature on effectiveness and the criteria for developing the baseline probabilities used in model were not stated. The model therefore could be open to bias if a non-systematic approach to identifying the literature has been adopted.
Validity of estimate of costs Sufficient details were provided of the costs used in the analysis. However, it would have been helpful if the authors had collated all cost information in one table as this would help the reader easily to identify the sources of total costs in the analysis. It was noted that the authors considered discounting the model but determined that this was not appropriate. It would, however, have been useful to consider possible discounting in a sensitivity analysis of the model. The cost limitations of the model were noted, such as outpatient treatment costs, and further economic evaluations may also wish to evaluate costs from different perspectives such as those of the patient, caregivers and society.
Other issues The costs reported in the analysis are unlikely to be generalisable to settings beyond the drug treatment centre used in the study. Additionally, reporting an incremental economic analysis evaluating the additional costs and benefits of direct observation compared with self administered chemoprophylaxis, would have been appropriate in identifying the added merit of direct observation
Implications of the study Further economic evaluations are required alongside clinical evaluations to consider the use of direct observation for this study group and other populations for whom issues of compliance are important.
Source of funding Grants from the National Institute of Drug Abuse (#R01 DA 09521 and #R01 DA04347), NY State AIDS Institute (#814-2300C-6508) and New York City Department of Health (#090085).
Bibliographic details Gourevitch M N, Alcabes P, Wasserman W C, Arno P S. Cost-effectiveness of directly observed chemoprophylaxis of tuberculosis among drug users at high risk for tuberculosis. International Journal of Tuberculosis and Lung Disease 1998; 2(7): 531-540 Indexing Status Subject indexing assigned by NLM MeSH Antibiotic Prophylaxis /economics; Antitubercular Agents /economics /therapeutic use; Cost-Benefit Analysis; Female; Humans; Isoniazid /economics /therapeutic use; Male; New York; Patient Compliance; Risk Factors; Substance-Related Disorders /economics /rehabilitation; Tuberculin Test /economics; Tuberculosis /economics /prevention & control AccessionNumber 21998001037 Date bibliographic record published 30/06/2000 Date abstract record published 30/06/2000 |
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