Understanding the impact of changing behavior on sexually transmitted infection (STI) incidence is vital to address the STI epidemic, according to a recent study published in Infectious Disease Modelling.
Takeaways
- From 2012 to 2019, there was a significant increase in reported cases of gonorrhea (GC) and chlamydia (CT), with nearly all demographic groups affected. In 2019 alone, there were 1,808,703 CT cases and 616,392 GC cases reported to the CDC.
- Factors contributing to STI transmission range from sexual behaviors, sexual networks, and healthcare access to societal values and policies. These multifaceted factors make addressing the STI epidemic complex.
- An agent-based stochastic network model was developed to understand the impact of changing behaviors on STI incidence. This model involved 50,000 individuals, categorized sexual partnerships, and presented various epidemiological aspects.
- While a 2% decrease in condom use between 2011-2013 and 2017-2019 did not have a significant impact on STI diagnoses, a decline in penile-vaginal sex (PVS) frequency led to notable reductions in both GC and CT diagnoses. Additionally, changes in testing contributed to increased diagnosis rates.
- The research suggests that PVS frequency is the primary source of STI transmission, with changes in this behavior significantly impacting the incidence rates of both GC and CT. Understanding these sources is crucial for addressing the increasing number of STI cases.
Nearly all demographic groups saw increased rates of gonorrhea (GC) and chlamydia (CT) from 2012 to 2019, with 1,808,703 CT cases and 616,392 GC cases reported to the Centers for Disease Control and Prevention (CDC) in 2019. Adverse outcomes of STIs include anxiety, infertility, relationship strife, and childhood disabilities.
As drug-resistant strains emerge, it is becoming more difficult to treat new infections. Factors behind STIs include sexual behaviors, sexual networks, health care seeking, health-care access, health system policies, provider bias, societal values, socioeconomic issues, and policies.
To determine the impact of changing behaviors on STI incidence, investigators designed an agent-based stochastic network model. The model included 50,000 individuals, sexual partnerships, and epidemic GC and CT transmission models. Three sexual partnership types were identified: main partnerships, casual but persistent partnerships, and one-time sexual contact.
Partnerships were formed based on age, race and ethnicity, age difference, sex-specific age asymmetry, and the presence or absence of other relationships. The epidemic model presented demography, interhost epidemiology, intrahost epidemiology, and clinical epidemiology.
Stochastic modeling was used to measure GC and CT transmission, with a fixed probability of acquiring a new infection during each condomless penile-vaginal sex (PVS) act. Recovery was determined 1 week after treatment, and recovered individuals were considered susceptible to reinfection.
To measure model efficacy, investigators ran the calibrated simulation 10,000 times, with each simulation lasting 120 years. The number of PVS acts and condom use per sex act were the primary behaviors evaluated.
According to the CDC, 106.7 GC and 453.4 CT diagnoses per 100,000 population were reported in 2012 and increased to 187.8 and 551.0 per 100,000 respectively in 2019. In the model, GC incidence was a mean 0.91 per 100 person-years at risk and CT incidence a mean 3.17 per 100 person-years at risk.
A 2% decrease in condom use was observed between 2011 to 2013 and 2017 to 2019, but this decline alone did not significantly impact GC or CT diagnosis. However, declining PVS frequency reduced GC and CT diagnosis rates by 6% and 3% respectively, and incidences by 10% and 9% respectively.
Changes in testing led to a 14% and 13% increase in GC and CT diagnosis rates respectively. These changes accounted for 17.7% of the change in CDC-reported diagnosis rates from 2012 to 2019 for GC and 58.2% for CT.
Overall, changes in behavior led to a 6.6% increase in CT diagnoses and a 6.3% increase in CG diagnoses in 2019. Changes in incidence rates caused by PVS frequency and all behaviors were virtually indistinguishable, indicating PVS frequency is the primary source of infection.
These results highlighted the impact of changing behaviors on STI diagnosis rates. Investigators concluding understanding sources of STI incidence is vital to address the increase in cases.
Reference
Hamilton DT, Katz DA, Haderxhanaj LT, Copen CE, Spicknall IH, Hogben M. Modeling the impact of changing sexual behaviors with opposite-sex partners and STI testing among women and men ages 15–44 on STI diagnosis rates in the United States 2012–2019. Infectious Disease Modelling. 2023;8(4):1169-1176. doi:10.1016/j.idm.2023.10.005
