This study used mathematical modelling and economic methods to evaluate the impact of the Jyoti Sangh HIV prevention project for CSWs in Ahmedabad. The project reached about three-quarters of the estimated CSW population in the city by the end of 2003 and involved three major components which have a direct impact on HIV transmission: promotion and distribution of condoms; free STD treatment; and counselling and behavioural change through peer education. For the period from the beginning of September 1999 to the end of November 2003 (51 months in total), the model projected that the intervention averted about half of the HIV infections that would have occurred amongst CSWs and clients in Ahmedabad without the intervention. The total number of HIV infections averted was estimated to be 5,755 (Uncertainty range: 2,548–10,140), and the cost-effectiveness ratio ranged from USD 38 to USD 133 per HIV infection averted when peer educator costs were excluded. When the peer educator costs were included the ratio ranged from USD 56 to USD 219.
Based on mathematical modelling, it has been suggested that sex worker interventions could drive the Indian HIV epidemic "to extinction"
]. By assuming the proportion of unprotected sexual contacts reduces from 67% to 25% through condom promotion among CSWs and their clients, Nagelkerke et al
] predicted a fivefold decrease in the HIV prevalence in India after 30 years compared to if no intervention had occurred. For comparison, STI management alone, when assumed to result in a 30% reduction in HIV transmission, made the HIV prevalence decrease two- to threefold. Given these long-term impact predictions, it is important that effective interventions such as the Jyoti Sangh project are continued. Even though the model predicts that this intervention resulted in a 50% reduction in incident infections, there was still a modest increase in HIV prevalence observed from 1999 to 2003. This emphasizes the importance of using modelling to estimate the impact of HIV prevention projects and highlights that more may need to be done to reduce HIV incidence in this setting.
In a recent international initiative to evaluate the cost-effectiveness of various strategies to combat HIV/AIDS in developing countries, the cost per HIV infection averted of peer education and treatment of STI for CSWs in World Health Organisation South East Asia Region (Sear-D region), of which India is a member, was found to be 45, 47 and 50 international dollars (year 2000) given a coverage level of 50%, 80% and 95% respectively [31
]. Our cost per HIV infection averted converts to the international dollar equivalent of 290 (excluding peer educator economic costs). The difference in these estimates can be attributed to differences in methodology to both costing and modelling of the impact. For example, Hogan et al
] will have produced much greater impact projections because they compared their intervention impact against the hypothetical 'no condom use' and 'no STI treatment' scenario, and estimated the impact amongst the general population. Also, it is unclear whether their cost estimates include the value of peer educator time. Indeed, rarely are these costs included in the costing of HIV prevention projects which maybe due to the different motivations of traditional volunteers who might forego earnings and peer educators who may actually acquire additional benefits from working in this manner. Together with the uncertainty in these values identified in this study, this lack of evidence calls for improved methods for understanding of peer educator time allocated to education activities and the value of their time to increase our confidence in the estimates and their impact on cost-effectiveness. However, the results compare favourably with interventions in sub-Saharan Africa, where the cost per DALY save for CSW peer education projects was estimated to be between 4.5 and 7.9 USD (2004 prices) [32
]. In addition, the undiscounted lifetime costs of AIDS illness in India is approximately USD 1200 [33
]. Thus given the limited access to HAART in India, if we assume no HAART, preventing the number of infections as predicted in the model would result in a cost saving of between USD 3.1 –12.1 million. With HAART, the savings would be much greater.
There is a less difference between the results from Jyoti Sangh and other studies using locally collected data. The results from 32 other HIV intervention programmes among CSWs in Tamil Nadu and Andhra Pradesh [34
], reveal costs per CSW reached ranging from 5 USD to 50 USD. Also from these studies it is apparent that the programme in Ahmedabad had greater scale than most of its counterparts in the two southern states, with only three programmes in Andhra Pradesh reaching greater numbers of CSWs (3,847, 4,690 and 6,379 respectively in fiscal year 2002–2003) [35
]. In contrast, the proportion of CSWs using STD services per month (2.8%–4.1%) in Ahmedabad was much lower than the number of CSWs/clients referred for STI treatment per CSW reached in any of the south Indian projects in one of the former studies [34
]. However, this difference could be because a low proportion of those referred are using services. In addition, as noted in the results, this proportion was not significantly associated with the impact projections of the Jyoti Sangh project. Indeed, it is likely that unless there is a significant increase in the number of CSWs or clients attending the Jyoti Sangh STI clinics, the clinics will have negligible effect on HIV and STI transmission in Ahmedabad. Despite this, the clinics are still likely to provide a beneficial point of contact for CSWs and their clients.
Our mathematical model was limited to the sexual relationships between CSWs and their clients, and excluded any HIV and STI transmission to other partners. No attempt was made to estimate the impact of the intervention programme upon the general population beyond the clients, and so our impact projections are likely to underestimate the real impact of the project. In addition, the model simulated the transmission of all the STIs together and so did not separate cofactors for each STI. This may have reduced the accuracy of our projections. Limitations in data, especially amongst the clients, resulted in substantial uncertainty in our impact estimates. Improvements in routine data collection and management, will certainly improve the quality of future impact estimations.
We did not incorporate the evolving nature of the intervention programme into the model. In reality, the intervention programme has been increasing in coverage, and improving their service through feedback from peer educators and gaining experience through practice. This increases the uncertainty in our estimates of coverage parameters. However, the model uncertainty analysis and fitting procedures minimized the effects of this uncertainty on the model predictions.
There were some differences between the sampling methods used in the two surveys, and in the survey estimates for the state of origin of the CSWs, and the proportions living with a husband or alone (Table A2). They were not adjusted in the model, and were a common limitation of analyses that use data not collected for modelling purposes.
Another limitation of the analysis was that HSV-2 transmission was not modelled as discussed in the Methods. This was due to a lack of applicable HSV-2 prevalence data. However, it is unlikely that the intervention would substantially affect the prevalence of HSV-2 over 33 months because of its likely high prevalence in this population and the fact that it cannot be cured.
Recall bias in the two surveys is a limitation in this study, as it is hard to determine to what extent the data collected reflect reality except that the large drop in STI prevalence concords with the reported decreases in risk behaviour.