Cost-effectiveness of HIV prevention interventions in Andhra Pradesh state of India

The Andhra Pradesh State AIDS Control Society (APSACS) is the nodal agency that facilitates a variety of public-funded HIV prevention interventions. Four of these interventions are based in clinical settings: voluntary counselling and testing (VCT) centres, prevention of parent to child transmission (PPTCT) centres, sexually transmitted infection (STI) clinics, and blood banks. VCT and PPTCT are now offered at the same facility referred to as integrated counselling and testing (ICT) centre. Eight interventions are implemented by non-governmental organisations targeting groups at high-risk of HIV: women sex worker (SW) programmes, men who have sex with men (MSM) programmes, truckers programmes, composite programmes, workplace programmes, migrant labourer programmes, street children programmes, and prisoner programmes. In addition, APSACS implements a state-wide information, education and communication (IEC) programme for the general public (mass media campaigns), and previously used to implement the state-wide condom promotion programme. Of the total 551 programmes facilitated by APSACS during the April 2005 to March 2006 fiscal year, a representative sample of 128 programmes was selected (Table 1) [4]. Data on the HIV prevention services provided by these programmes, and the economic cost of the programmes including personnel, recurrent goods, recurrent services, capital goods and office space rentals, were documented from written records and interviews of programme staff by trained investigators using procedures described previous that included quality control [4‐10]. The adolescent education awareness programme for HIV prevention that is facilitated by the State Council of Education Research and Training was not included in this assessment.

We have previously reported the total HIV prevention services provided through APSACS facilitated programs and the economic cost of these services in Andhra Pradesh in the 2005-2006 fiscal year, and based on the estimated intervention effect per unit service we have reported the number of HIV infections averted by each intervention in this year along with the uncertainty range calculated from sensitivity analysis with Monte Carlo simulations using random values of input variables (Table 2) [4]. This method and the detailed calculations of HIV infections averted by each intervention are shown in Additional file 1 as compared with the situation if there was no intervention at all. From this we calculated the cost per HIV infection averted during the 2005-2006 fiscal year by each type of prevention intervention for the services provided in Andhra Pradesh during this year. We then calculated Disability Adjusted Life Years (DALYs) saved as the sum of the Years of Life Lost (YLL) and the Years Lost due to Disability (YLD) that would be saved for each HIV infection averted by each prevention intervention using published methods [11‐14].

Where a = age at death in years; L = standard expectation of life in years at age a; r = discount rate; K = age-weighting modulation factor; C = age-weighting adjustment constant; β = constant from the age-weighting function.

Where a = age at onset of disability in years; L = duration of disability in years; D = disability weight; r = discount rate; K = age-weighting modulation factor; C = age-weighting adjustment constant; β = constant from the age-weighting function.

We used the commonly used discount rate r = 0.03, i.e. 3% yearly discount rate for the value of years of life lost in the future. For calculation of DALYs with age-weighting, previously suggested values for constants were used: K = 1, C = 0.1658 and β = 0.04. As the use of age-weighting in the calculation of DALYs is controversial due to preferential weights given to young adults as compared with children and elderly, we calculated DALYs without age-weighting in which the value of the age-weighting modulation factor K = 0 and C and β become not applicable.

Based on estimated local trends, for sexually acquired HIV in adults the average age at infection was assumed as 30 years for men and 25 years for women. For sexually acquired HIV in street children, the average age at infection was assumed as 17 years for both boys and girls based on estimated local trends. The age at infection for mother to child transmission of HIV was considered as the first year of life. The average age at infection from blood transfusion was estimated as 5 years in the 14 years and less age group, 30 years in the 15-44 years age group, and 50 years in the 45 years and above age group, based on local trends. DALYs were calculated separately for men and women and a weighted average calculated based on the proportion of HIV infections averted in men and women by each intervention.

The YLDs were calculated separately for pre-AIDS and AIDS. The duration of HIV to pre-AIDS was considered as 6 years, from pre-AIDS to AIDS as 2 years, and from AIDS to death as 1.5 years without anti-retroviral treatment [15]. As a very small fraction of persons with HIV/AIDS were on antiretroviral treatment in India at the time of this study, we calculated DALYs saved without including prolonged life and additional cost due to antiretroviral treatment. This would have to be re-considered as the antiretroviral treatment becomes more common.

DALYs saved for each HIV infection averted by each intervention were computed with and without age-weighting as YLLs + YLDs (Pre AIDS) + YLDs (AIDS). Utilising the cost per HIV infection averted computations, we then calculated the cost per DALY saved for each intervention. Cost in Indian Rupees (INR) was converted to US$ using the average exchange rate of INR 44.27 for a US$ in the 2005-2006 fiscal year [16]. We calculated the uncertainty range of these estimates based on the 5^th and 95^th percentile values of HIV infections averted by each intervention computed previously with sensitivity analysis through 100,000 iterations each by Monte Carlo simulations using the @Risk software (Palisade Corporation, Newfield, New York, USA).