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Cost-effectiveness of an HIV/AIDS prevention intervention for gay men |
Holtgrave D R, Kelly J A |
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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 An HIV/AIDS prevention intervention for gay men.
Study population The study population consisted of gay men who had engaged in behaviour with a high risk of HIV infection.
Setting The setting was a medical school outreach programme. The economic study was carried out in the USA.
Dates to which data relate Effectiveness data were collected from studies published between 1989 and 1995. Cost data were taken from studies published between 1987 and 1994. The price year was 1993.
Source of effectiveness data Effectiveness data were derived from a literature review.
Modelling The authors used a standard, cumulative-probability, Bernoullian model of HIV transmission to calculate the number of HIV infections averted. They used a per-act model, which assumes that each sex act poses some risk of infection, and a per-partner model, which assumes that each new partnership poses a risk of HIV infection. The authors used a method described in another paper to convert the number of HIV infections averted into the number of quality-adjusted life years (QALYs) saved.
Outcomes assessed in the review The review assessed HIV seroprevalence, transmission probabilities, condom effectiveness, the number of contacts with one partner, the number of partners, and QALYs.
Study designs and other criteria for inclusion in the review Effectiveness estimates were derived from one major, randomised controlled trial which involved 104 gay men, as well as other studies.
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 Seven primary studies were included.
Methods of combining primary studies Investigation of differences between primary studies Results of the review HIV seroprevalence of the sex partner was 0.2.
Probabilities of single-sex-act transmission and single-sex-partner transmission were 0.009 and 0.1, respectively.
Condom effectiveness was 0.95.
Condom use per sex act in the intervention group was 23% at baseline, 65% at 4-month follow-up, and 77% at 8-month follow-up.
Condom use per sex act in the control group was 24% at baseline, and 19% at 4-month follow-up.
The number of contacts with one partner was 3.2.
The number of partners per client was 5.
The number of QALYs saved per prevention was 7.32.
Methods used to derive estimates of effectiveness The authors made a number of assumptions.
Estimates of effectiveness and key assumptions The authors assumed that HIV seroprevalence among intervention participants was approximately one half that in the population of sex partners of intervention participants. They also assumed that men engaged in anal intercourse once every other week.
Measure of benefits used in the economic analysis The number of HIV infections averted and QALYs were used as the measures of benefit. QALYs were discounted at an annual rate of 5%. The authors used a method described in another paper to convert the number of HIV infections averted into the number of QALYs saved.
Direct costs Direct costs were not discounted given the time horizon of less than one year, except for the cost of treating a case of HIV disease and AIDS, which was discounted at an annual rate of 5%. Quantities and costs were reported separately. Direct costs included costs of wages and fringe benefits and material costs. The quantity/cost boundary adopted was that of the hospital. Costs and quantities were obtained from published sources. The price year was 1993.
Statistical analysis of costs No statistical analyses were reported.
Indirect Costs Indirect costs were not discounted given the time horizon of less than one year. Quantities and costs were reported separately. Indirect costs were stated to be: the costs of utilities, rent, maintenance, and general administration (which were estimated as a fraction of direct costs (indirect cost rate)); costs of recruitment to the intervention, costs of time spent in the intervention sessions and en route to and from sessions, and transportation costs. However, only time is strictly an indirect cost. This was valued at $17 per hour based on the prevailing wage rate and 94% employment and was referred to as "opportunity costs" by the authors. The quantity/cost boundary adopted was that of society. Costs and quantities were obtained from published sources. The price year was 1993.
Sensitivity analysis Sensitivity analyses were conducted on sex partners' HIV seroprevalence, condom effectiveness, condom use with intervention per act, number of contacts with one partner, number of partners per client, number of clients in the intervention, indirect cost rate, opportunity cost, medical treatment costs, and number of QALYs saved.
Estimated benefits used in the economic analysis The number of HIV infections averted was 0.75 for 50 clients. The number of QALYs was not reported separately, but should be easy to calculate if required.
Cost results The total societal cost of the intervention was $23,507, or $470 per client. The discounted medical treatment cost for HIV and AIDS was $56,000.
Synthesis of costs and benefits Cost-utility was calculated by the formula: I-AT/QA, where I = total societal cost; A = number of HIV infections averted; Q = number of QALYs per HIV infection averted; and T = discounted medical treatment cost for HIV/AIDS.
In the base case this produced a cost saving in both the per-act and per-partner models.
Sensitivity analyses revealed that the cost-utility moved above $50,000 only when, in the per act model, the following conditions were met: a single-sex-act transmission of rate of 0.002, an A value of 0.171 and either seroprevalence of 0.05, 1 partner per client or 1 contact with one partner.
Authors' conclusions "The small group, workshop-format, cognitive-behavioural HIV-prevention intervention for gay men was cost saving. The results were generally robust to changes in model parameters and assumptions".
CRD COMMENTARY - Selection of comparators A justification was given for the comparator used, namely to determine efficacy by ethical means. You, as a user of the database, should decide if there are any other health technologies that are relevant to your setting.
Validity of estimate of measure of effectiveness The authors undertook a literature review to derive effectiveness estimates, but they did not state that a systematic review of the literature had been undertaken. The review generated only one randomised controlled trial from which most effectiveness estimates were taken, and the method of combination of estimates was not stated. Also, the validity of the assumptions needs to be scrutinised. However, the validity of the results was enhanced by sensitivity analyses to account for variability in the estimates.
Validity of estimate of measure of benefit The estimation of the number of HIV infections averted was obtained directly from the effectiveness analysis. The authors used a method described in another paper to convert the number of HIV infections averted into the number of QALYs saved.
Validity of estimate of costs A good features of the cost analysis was that all relevant direct and indirect cost categories were included, although placed in unusual categories. The validity of the cost results was enhanced by appropriate sensitivity analyses, and quantities and costs were reported separately thus enhancing the generalisability of the results. The price year was reported which would make reflation exercises in other settings possible.
Other issues The authors did not make appropriate comparisons of their findings with those from other studies, but the issue of generalisability to other settings was addressed and the authors did not appear to present their results selectively. The study considered gay men who had engaged in high-risk behaviours for HIV infection and this was reflected in the authors' conclusions. The authors did admit certain limitations. For example, they did not consider the start-up costs of the intervention, and effectiveness estimates were derived from a trial with a short time-frame allowing the use of a simpler model than a dynamic compartmental epidemic model.
Implications of the study Given the conclusions of the study, the authors suggested that: "Such behavioural interventions should receive serious consideration for investment by public health decision makers allocating fiscal resources for health services". This recommendation should be viewed in the context of the validity of estimates of parameters and the cost-utility of other competing technologies.
Source of funding Supported in part by Grants R01-MH55440 and P30-MH52776 from the National Institute of Mental Health.
Bibliographic details Holtgrave D R, Kelly J A. Cost-effectiveness of an HIV/AIDS prevention intervention for gay men. AIDS and Behavior 1997; 1(3): 173-180 Indexing Status Subject indexing assigned by CRD MeSH Acquired Immunodeficiency Syndrome /prevention & Adult; Condoms; Cost-Benefit Analysis; Male; Outcome and Process Assessment (Health Care); Preventive Health Services /economics; Quality-Adjusted Life Years; Risk Factors; Sexual Behavior; Urban Population; control /economics AccessionNumber 21998007589 Date bibliographic record published 31/01/2002 Date abstract record published 31/01/2002 |
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