State-level gonorrhea rates and expedited partner therapy laws: insights from time series analyses.

OBJECTIVE: In this study, we examined state-level monthly gonorrhea morbidity and assessed the potential impact of existing expedited partner therapy (EPT) laws in relation to the time that the laws were enacted. STUDY DESIGN: Longitudinal study. METHODS: We obtained state-level monthly gonorrhea morbidity (number of cases/100,000 for males, females and total) from the national surveillance data. We used visual examination (of morbidity trends) and an autoregressive time series model in a panel format with intervention (interrupted time series) analysis to assess the impact of state EPT laws based on the months in which the laws were enacted. RESULTS: For over 84% of the states with EPT laws, the monthly morbidity trends did not show any noticeable decreases on or after the laws were enacted. Although we found statistically significant decreases in gonorrhea morbidity within four of the states with EPT laws (Alaska, Illinois, Minnesota, and Vermont), there were no significant decreases when the decreases in the four states were compared contemporaneously with the decreases in states that do not have the laws. CONCLUSION: We found no impact (decrease in gonorrhea morbidity) attributable exclusively to the EPT law(s). However, these results do not imply that the EPT laws themselves were not effective (or failed to reduce gonorrhea morbidity), because the effectiveness of the EPT law is dependent on necessary intermediate events/outcomes, including sexually transmitted infection service providers' awareness and practice, as well as acceptance by patients and their partners.

Cost-effectiveness of a 12-dose regimen for treating latent tuberculous infection in the United States.

SETTING: A large randomized controlled trial recently showed that for treating latent tuberculous infection (LTBI) in persons at high risk of progression to tuberculosis (TB) disease, a 12-dose regimen of weekly rifapentine plus isoniazid (3HP) administered as directly observed treatment (DOT) can be as effective as 9 months of daily self-administered isoniazid (9H). OBJECTIVES: To assess the cost-effectiveness of 3HP compared to 9H. DESIGN: A computational model was designed to simulate individuals with LTBI treated with 9H or 3HP. Costs and health outcomes were estimated to determine the incremental costs per active TB case prevented and per quality-adjusted life year (QALY) gained by 3HP compared to 9H. RESULTS: Over a 20-year period, treatment of LTBI with 3HP rather than 9H resulted in 5.2 fewer cases of TB and 25 fewer lost QALYs per 1000 individuals treated. From the health system and societal perspectives, 3HP would cost respectively US$21,525 and $4294 more per TB case prevented, and respectively $4565 and $911 more per QALY gained. CONCLUSIONS: 3HP may be a cost-effective alternative to 9H, particularly if the cost of rifapentine decreases, the effectiveness of 3HP can be maintained without DOT, and 3HP treatment is limited to those with a high risk of progression to TB disease.

Sexuality education policies and sexually transmitted disease rates in the United States of America.

The aim of the study was to test for relationships between state-level sex educational policies and sexually transmitted disease (STD) rates. We analysed US case reports of gonorrhoea and chlamydial infection for 2001-2005 against state policies for abstinence coverage in sexuality education, using the proportion of the population per state who identified as black (aged 15-24 years) as a covariate. We also tested for effects on 15-19 year olds versus 35-39 year olds and tuberculosis rates (the latter to ensure findings applied only to STD). States with no mandates for abstinence had the lowest mean rates of infection among the overall population and among adolescents. States with mandates emphasizing abstinence had the highest rates; states with mandates to cover (but not emphasize) abstinence fell in between. Rates in some states covering abstinence changed faster than in others, as reflected in sharper declines (gonorrhoea) or slower increases (chlamydial infection). These effects were not shown for tuberculosis or 35-39 year olds. Having no abstinence education policy has no apparent effect on STD rates for adolescents. For states with elevated rates, policies mandating coverage may be useful, although policies emphasizing abstinence show no benefit.

All STDs are not created equal: an analysis of the differential effects of sexual behaviour changes on different STDs.

The same sexual behaviours that transmit HIV are implicated in the transmission of certain other STDs, including chlamydia, gonorrhoea, and syphilis. Consequently, it is often assumed that preventive methods that are effective against HIV should be equally effective against other STDs. The purpose of this study was to examine this assumption. We applied a mathematical model of HIV/STD transmission to empirical data from a large HIV prevention intervention that stressed sexual behaviour change. We modelled the effects of two behavioural strategies - reducing the number of sex partners and increasing condom use-on the proportionate change in intervention participants' cumulative risk of acquiring HIV or a highly-infectious STD, such as gonorrhoea. The results of this modelling exercise indicate that decreasing the number of partners is a more effective strategy for reducing STD risk than it is for HIV risk. In contrast, condoms are somewhat more effective at reducing the cumulative transmission risk for HIV than for highly infectious STDs. The protection provided by condoms for multiple acts of intercourse critically depends on the infectiousness of the STD. The results of this study suggest caution in extrapolating from one STD to another, or from one behavioural risk reduction strategy to another.

When is an HIV infection prevented and when is it merely delayed?

HIV prevention programs are typically evaluated using behavioral outcomes. Mathematical models of HIV transmission can be used to translate these behavioral outcomes into estimates of the number of HIV infections averted. Usually, intervention effectiveness is evaluated over a brief assessment period and an infection is considered to be prevented if it does not occur during this period. This approach may overestimate intervention effectiveness if participants continue to engage in risk behaviors. Conversely, this strategy underestimates the true impact of interventions by assuming that behavioral changes persist only until the end of the intervention assessment period. In this article, the authors (a) suggest a simple framework for distinguishing between HIV infections that are truly prevented and those that are merely delayed, (b) illustrate how these outcomes can be estimated, (c) discuss strategies for extrapolating intervention effects beyond the assessment period, and (d) highlight the implications of these findings for HIV prevention decision making.

Sexually transmitted diseases and the increased risk for HIV transmission: implications for cost-effectiveness analyses of sexually transmitted disease prevention interventions.

We estimated the annual number and cost of new HIV infections in the United States attributable to other sexually transmitted diseases (STDs). We used a mathematical model of HIV transmission to estimate the probability that a given STD infection would facilitate HIV transmission from an HIV-infected person to his or her partner and to calculate the number of HIV infections due to these facilitative effects. In 1996, an estimated 5,052 new HIV cases were attributable to the four STDs considered here: chlamydia (3,249 cases), syphilis (1,002 cases), gonorrhea (430 cases), and genital herpes (371 cases). These new HIV cases account for approximately $985 million U.S. in direct HIV treatment costs. The model suggested that syphilis is far more likely than the other STDs (on a per-case basis) to facilitate HIV transmission. This analysis provides a framework for incorporating STD-attributable HIV treatment costs into cost-effectiveness analyses of STD prevention programs.

The increasing marginal benefit of condom usage.

PURPOSE: Condom use is promoted as a primary strategy for preventing sexual transmission of human immunodeficiency virus (HIV). This paper analyzes how incremental changes in condom compliance rates can affect an individual's risk of acquiring HIV. METHODS: We developed a simple mathematical model of HIV transmission in which the cumulative probability of HIV infection depended in part upon the percentage of acts in which a condom was used. We applied basic methods of calculus to differentiate the mathematical model with respect to the probability of condom usage. We applied values from published studies to the model to illustrate how the marginal benefits of condom usage vary across different populations. RESULTS: In general, the marginal benefit of condom usage increases as condom compliance increases. CONCLUSIONS: The marginal benefits of increased condom usage vary across different risk groups and across different levels of condom compliance. These results offer insight into the motivation behind the decision of whether or not to use condoms, and indicate possible ways to optimize the use of resources devoted to increasing condom usage by at-risk populations.

New HIV cases attributable to syphilis in the USA: estimates from a simplified transmission model.

OBJECTIVE: Because syphilis can raise the likelihood of HIV transmission and acquisition, syphilis prevention in the USA has the potential benefit of reducing the number of new cases of HIV. We developed a simplified transmission model to estimate the annual number and cost of new, heterosexually-acquired HIV cases in the USA attributable to syphilis. DESIGN: We estimated the number of heterosexual, HIV serodiscordant partnerships in which syphilis was present in 1996. The model included the probability of transmission of HIV (with and without the presence of syphilis) and other parameters based on data from recent literature. Published direct costs (HIV treatment costs including antiretroviral therapy) and indirect costs (e.g., lost productivity) per case of HIV were used to estimate the annual cost of HIV cases attributable to syphilis. The potential savings in averted HIV costs related to syphilis were used to estimate the potential benefits of a syphilis elimination program. RESULTS: In 1996, an estimated 1082 new heterosexual cases of HIV in the USA could be attributed to syphilis. These cases represented direct costs of US$ 211 million and indirect costs of US$ 541 million; yielding US$ 752 million in total costs. Over 15 years, a syphilis elimination program could save over US$ 833 million (discounted at 3% annually) in averted direct medical costs of syphilis-related HIV infections. CONCLUSIONS: If the only benefit of syphilis elimination were to prevent new HIV cases attributable to syphilis, a national syphilis elimination program costing less than US$ 833 million would probably pay for itself.

Alternative approaches to valuing intangible health losses: the evidence for multiple sclerosis.

This study uses both risk-risk and risk-dollar approaches to assess intangible health losses associated with multiple sclerosis (MS). Using an estimation approach that adjusts for potential perceptional biases that may effect the expressed risk tradeoffs, we estimated parameters of the utility function of persons with and without MS as well as the degree of subjects" overestimation of the probability of obtaining MS. The sample included subjects from the general population and persons with MS. We found that marginal utility of income is lower in the state with MS than without it. However, the difference in marginal in two states was greater for persons without MS than for those with the disease. Persons with MS overestimated the probability of acquiring MS to a greater extent than did persons within MS. Correcting for overestimation of this probability, the value of intangible loss of a statistical case of MS derived from responses of the general population was US$350,000 to US$500.000. Persons with MS were willing to pay somewhat more than this (D80,118,J17).