Table 1.

Probabilities, costs, and other inputs used in decision tree analysis of the lifetime medical cost of chlamydia, gonorrhea, and trichomoniasis in men and women, per infection: Base case value (range)

Model input	Chlamydia		Gonorrhea		Trichomoniasis
	Men	Women	Men	Women	Men	Women
Probabilities
Probability that infection is symptomatic*	0.158 (0.082–0.262)	0.254 (0.177–0.344)	0.589 (0.314–0.830)	0.314 (0.155–0.510)	0.081 (0.051–0.224)	0.192 (0.118–0.328)
Probability of treatment, symptomatic infection*	0.936 (0.893–0.967)	0.894 (0.855–0.931)	0.744 (0.621–0.846)	0.750 (0.631–0.846)	0.406 (0.150–0.749)	0.876 (0.586–0.949)
Probability of treatment, asymptomatic infection*	0.137 (0.092–0.213)	0.241 (0.208–0.276)	0.020 (0.012–0.034)	0.068 (0.043–0.111)	0.000	0.000
Probability of sequelae, treated symptomatic infection†	0.003	0.003	0.003	0.003	Not applicable	Not applicable
Probability of sequelae, treated asymptomatic infection†	0.003	0.063 (0.01–0.12)	0.003	0.063 (0.01–0.12)	Not applicable	Not applicable
Probability of sequelae, untreated infection†	0.026 (0.01–0.04)	0.129,10 (0.02–0.24)	0.026 (0.01–0.04)	0.129,10 (0.02–0.24)	Not applicable	Not applicable
Cost and cost-related inputs
Treatment of infection, non-STI clinic‡	$1607 (134–186)	$1527 (134–170)	$1743,7 (102–319)	$1273,7 (72–237)	$1588 (145–171)	$2208 (209–231)
Treatment of infection, STI clinic§	$953,11 (80–110)	$953,11 (80–110)	$953,11 (80–110)	$953,11 (80–110)	$953,11 (80–110)	$953,11 (80–110)
Proportion treated in STI clinic setting	0.1011	0.0401	0.1201	0.0671	0.110	0.053
Treatment of infection, average across settings¶	$153 (129–178)	$150 (132–168)	$165 (99–294)	$125 (73–228)	$151 (138–164)	$213 (202–225)
Treatment of sequelae‖ (Epididymitis among men, PID among women)	$37512 (232–518)	$2,454 (1,913–3,677)3,13	$37512 (232–518)	$2,454 (1,913–3,677)3,13	Not applicable	Not applicable

^*These probabilities were obtained from the models of chlamydia, gonorrhea, and trichomoniasis incidence and prevalence^4,5 in this Special Issue. For each input, the lower bound, base case, and upper bound values we applied corresponded to the 2.5^th percentile, median, and 97.5^th percentile, respectively, from the applicable model. See the appendix and these source studies^4,5 for more details.

^†As in the 2013 STI cost study by Owusu-Edusei and colleagues,³ we assumed (1) that the probability of sequelae following treatment of symptomatic infections was 0, under the reasoning that these infections are likely treated promptly, (2) that the probability of epididymitis was 0 for treated infections (asymptomatic and symptomatic), and (3) that no epididymitis or PID was attributable to trichomoniasis regardless of treatment status or symptom status. For chlamydia, the probability of PID was obtained from a model-based synthesis¹⁰ of data from the POPI (Prevention of Pelvic Infection) trial.⁹ Following the Owusu-Edusei study³ we assumed the same probability of PID for gonorrhea as for chlamydia.

^‡For chlamydia, the base case estimate of the cost of treatment for infection was obtained from a recent study of medical claims data for chlamydia and gonorrhea treatment,⁷ the upper bound was obtained the Owusu-Edusei study,³ and the lower bound was selected such that the base case estimate would be the midpoint of the lower and upper bound values. These choices for the lower and upper bound values allowed us to consider a wider range of possible values than implied by the 95% confidence intervals of the recent medical claims study ($153 to $167 for men; $148 to $156 for women).⁷ For gonorrhea, the lower bound value was obtained from the recent medical claims study,⁷ the upper bound value was obtained from the Owusu-Edusei study,³ and the base case value was a weighted average of these two values, in which the estimate from the more recent medical claims study was given a weight of 2/3 and the Owusu-Edusei estimate was given a weight of 1/3. For trichomoniasis, the base case value and range was obtained from a recent study of medical claims data for trichomoniasis treatment.⁸

^§For the cost of treatment of infection in STI clinic settings, we applied the same base case value and range for all three STIs. The lower bound value reflects the physician visit cost applied in the Owusu-Edusei study,³ the base case value was approximated using data on cost projections for an clinic offering a standard set of STI services (we used a slightly lower cost per clinic visit of $95 rather the $101 estimate implied by the source study for 2,153 visits under the assumption that a higher clinic volume could reduce the average cost incurred per STI clinic visit),¹¹ and the upper bound value was calculated such that the base case value would be the midpoint of the range.

^¶The average cost of treatment across settings (STI-clinic and non-STI clinic) was calculated based on the cost assumptions listed in the table for the STI clinic and non-STI clinic settings, along with the assumptions shown for the percentage of treated cases that are treated in an STI clinic. For trichomoniasis, the proportion treated in an STI clinic calculated as the average of the proportions listed for chlamydia and gonorrhea.

^‖For epididymitis, the base case cost estimate was calculated as the average of $341 and $409, which were the average cost estimates for patients in the “≥13 to <41 years” age group and patients in the “≥41 years” age group, respectively, as reported in a medical claims study.¹² The upper bound was based on the cost estimates for patients in the “<13 years” age group from that same study, and the lower bound value was selected such that the base case value would be the midpoint of the range. For PID, the base case value was calculated as shown in Table 2, the lower bound value was obtained from Gift and Rein (2004),¹³ and the upper bound value was obtained from the Owusu-Edusei study³ as described in the manuscript text.

PID: pelvic inflammatory disease; STI: sexually transmitted infection

All costs are in 2019 US dollars.