The study shows that the cost-effectiveness of the intervention depends on the sexual behavior of inmates. Even in a setting unfavorable to screening (no sexual activity among inmates) and with an intervention that screens 40% of inmates at intake and treats only 63% of identified infections, modeling indicates that large numbers of STIs could be averted at a low cost. The intervention could lead to cost-savings if incarcerated MSM continue to engage in sexual activity as they do outside jail. Higher levels of treatment and higher prevalence of infection result in more favorable cost-effectiveness estimates.
It should be noted that the scenarios presented here reflect uncertainty about sexual behavior in the MSM unit. Thus, the first (unfavorable) scenario provides a lower-bound estimate of intervention effectiveness and the third scenario the least conservative (most favorable) estimate; base case cost-effectiveness values should be interpreted as being located in the range delimited by the scenarios (Table 2).
Modeling indicates that screening and treatment for syphilis in the MSM unit is more cost-effective than similar interventions for chlamydia and gonorrhea. This study may have underestimated the cost-effectiveness of screening for HIV by not considering efforts by inmates who test positive to reduce the risk of transmitting infection to their partners after they leave the MSM unit. Even so, the intervention against HIV is cost saving in the third scenario.
In an economic evaluation of HIV counseling and testing in US prisons, Varghese and Peterman also concluded that the intervention is cost saving (even though they did not examine the effect of the intervention on future transmission).11 Similarly, Kraut et al. found screening of incarcerated men for syphilis to be cost saving.10 In their study, screening for chlamydia and gonorrhea was not cost-effective in preventing epididymitis (at a cost per case averted of $39,800 for chlamydial epididymitis and $421,579 for gonococcal epididymitis). However, they did not account for reduction in future STI transmission resulting from the intervention.
The benefits of the intervention are largely societal while the costs are incurred in the jail. Jail authorities are unlikely to see significant changes in STI care expenditures due to averted future infections since much of the decrease in the burden of infections occurs outside the MSM unit (especially in the scenario in which no sex occurs in the unit). In this context, continuation of screening activity in the future will probably depend on continuing personnel and financial support from the Los Angeles County Sexually Transmitted Disease Program.
The model used to study the effect of the intervention on STI transmission is based on the gonorrhea transmission model developed by Hethcote and Yorke.16 STI transmission dynamics are dependent on the existence of a highly sexually active (core) group that interacts with a less sexually active (noncore) group. Hethcote and Yorke have shown that interventions directed at identification and treatment of infected core group members can result in a much bigger impact on transmission than interventions delivered without regard to group membership. The present analysis does not address this question because it is unlikely that staff will be able to differentiate core group members from others before administering screening tests. However, if core group members enter the correctional system at a higher rate than noncore group members, the cost-effectiveness of a jail-based screening initiative is likely to be more favorable than found in this study.
We assumed that screening and treatment is completed during intake into the MSM unit. Delays in identification and successful treatment will reduce the number of infections averted in the unit. However, in the scenario in which no sex occurs in the unit, such delays do not alter transmission dynamics and the conservative cost-effectiveness findings of the study remain valid. A related issue is the tracking of individuals who test positive but leave the unit before receiving treatment. The base case treatment rate of 63% (among those who are screened and test positive) in the unit is conservative. The assumption is that the remaining individuals do not benefit from screening (even though costs are incurred in testing them). The cost-effectiveness of efforts to trace these individuals and treat them (in prisons or outside the correctional system) needs to be determined.
The present analysis underestimates the benefits of screening because transmission from MSM to women is not considered. If MSM engage in sexual activity with women after leaving the MSM unit, the intervention is likely to yield additional savings of treatment costs through prevention of pelvic inflammatory disease among female sex partners. The analysis also excludes productivity gains and intangible benefits such as pain and suffering averted by preventing future cases.
Additionally, the benefits of screening for chlamydia, gonorrhea, and syphilis are understated in the analysis for one other reason. STIs, especially syphilis, are known to facilitate HIV transmission.39,40 This mechanism is not considered in the analysis. Costs and benefits of antiretroviral therapy directed at inmates who test positive for HIV have also not been assessed in this study. Finally, the effect of continued condom use (after inmates leave the MSM unit) on future STI transmission has not been evaluated.
Future analyses should use model structures that account for differences between the STIs and between symptomatic and asymptomatic individuals and consider the impact of STIs on HIV transmission. Alternative analytical approaches to assessment of cost-effectiveness are also worth considering (e.g., comparing the intervention with another that attempts to identify highly sexually active individuals before screening). Finally, future evaluations should assess the cost-effectiveness of the intervention in an additional scenario in which MSM engage in a reduced level of sex after entering the unit.
In conclusion, using conservative assumptions, this study has found that the intervention could avert large numbers of STIs at a reasonable cost and can save costs in a scenario in which inmates continue to engage in sexual activity as they do outside jail. Modest success in efforts to promote condom use among inmates results in additional cost saving. Thus, allocation of funds to this intervention is a good public health investment.
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