TABLE 1.

Parameter Values Used in a Model to Estimate the Impact and Cost-Effectiveness of Screening MSM for Rectal Chlamydial and Gonococcal Infection to Prevent HIV

Parameter	Base Case	Lower Bound	Upper Bound	Source
Annual incidence rate of rectal CT/GC, MSM without HIV (λSTD)	0.041	0.026	0.062	Calculated*
Annual incidence rate of rectal CT/GC, MSM with HIV $\text{(}{\widehat{\lambda }}_{\text{STD}})$	0.129	0.084	0.160	Calculated*
Annual HIV incidence rate among those without rectal CT/GC (λHIV)	0.0124	0.0112	0.0134	13†
Relative risk of acquiring HIV among those with rectal CT/GC (ϴ)	1.9	1.2	2.6	1,13‡
Duration of CT/GC infection in the absence of screening (d), years	0.75	0.5	1	14,15
Lifetime number of QALYs lost per HIV case	6.95	4.85	9.05	19
Lifetime cost per case of HIV	$314,000	$236,000	$391,000	20,21
Cost of rectal CT/GC screening	$41	$25	$56	18,22
Cost of rectal CT/GC treatment	$50	$43	$58	18,23
Annual rate of rectal CT/GC screening among MSM without HIV	0.37	0.15	0.65	Assumed§
Annual rate of rectal CT/GC screening among MSM with HIV	0.58	0.25	1.00	Assumed§

All costs are in 2011 US dollars. For more information, see supplemental appendix, http://links.lww.com/OLQ/A58.

^*Incidence rates were approximated as prevalence rates divided by duration. Prevalence rates of 3.1% and 9.7% were estimated for MSM without and with HIV, based on 462 and 676 cases of rectal CT/GC detected, respectively, among approximately 15,131 and 6984 MSM screened, respectively. These estimated case numbers for rectal CT/GC reflect the assumption that rectal CT/GC cases for which HIV status was unknown were distributed in the same proportion as the known cases (SFDPH, unpublished data). The annual rates of screening shown in the bottom rows of the table correspond to annual probabilities of screening of 31% and 44% for MSM without and with HIV, respectively. Assuming 48,810 MSM without HIVand 15,873 MSM with HIV,¹³ there would be approximately 15,131 MSM without HIV (31% of 48,810) and 6984 MSM with HIV (44% of 15,873) screened each year. In the model, the number of MSM was rounded to 65,000, and HIV prevalence was rounded to 25%.

^†HIV incidence among MSM without rectal CT/GC was based on HIV incidence rates reported by SFDPH as follows. Assuming that (1) rectal CT/GC prevalence among MSM without HIV is 3.1%, (2) HIV incidence among MSM with rectal CT/GC is 2.36% (calculated as the weighted average among men with 0, 1, and 2 prior rectal infections in the previous 2 years),¹ and (3) HIV incidence among MSM overall is 1.27%, as reported in the 2010 SFDPH HIV/AIDS Annual Report,¹³ HIV incidence among those without rectal GC can be estimated as [0.0127 – (0.031 * 0.0236)]/(1 – 0.031) = 0.0124.

^‡The relative risk of acquiring HIV among those with rectal CT/GC was 1.9 (calculated as 0.0236 divided by 0.0124) in the base case, with a lower bound of 1.2 (0.0149/0.0124) and an upper bound of 2.6 (0.0326/0.0124). For the lower and upper bounds, the numerators (0.0149 and 0.0326) are from the 95% confidence interval of HIV incidence among those with rectal CT/GC from the 2010 study by Bernstein et al.¹

^§Based on STOP AIDS Behavioral Risk Assessments, San Francisco 2010 (personal communication, Jennifer Hecht to Kyle Bernstein, February 15, 2012), and adjusted for potential overreporting, as described in the supplemental appendix, http://links.lww.com/OLQ/A58.

CT/GC infection denotes CT and/or GC infection; CT/GC screening denotes screening for both CT and GC infections.