Condition Definition

Sexually transmitted infections (STIs) are infections that are principally transmitted through intimate physical contact and sexual activity.¹ STIs with the greatest extensive public health impact in the United States are human immunodeficiency virus (HIV), hepatitis B (HBV), herpes simplex virus (HSV) 1 and 2, human papillomavirus (HPV), Chlamydia trachomatis, Neisseria gonorrhea, Treponema pallidum (syphilis), and Trichomonas vaginalis.¹ Other conditions that can be spread through sexual contact include granuloma inguinale, chancroid, pubic lice, and Sarcoptes scabiei var. hominis (scabies). Bacterial vaginosis (BV), while not caused by a specific sexually transmitted pathogen, is an imbalance in the growth of normal vaginal microorganisms that is associated with sexual activity and is an included condition for this review.

Etiology and Natural History

STIs are caused by three main types of pathogens: bacteria, including Chlamydia (C.) trachomatis, Neisseria (N.) gonorrhea, and Treponema (T.) pallidum; viruses, such as HIV, HSV, HBV, and HPV; and parasites, including Trichomonas (T.) vaginalis. More than 30 different bacteria, viruses, and parasites are known to be acquired and spread through sexual activity, which includes vaginal, anal, and oral intercourse.² STIs can also be transmitted nonsexually via direct contact with bodily fluids (blood, saliva, semen) from an infected person (e.g., using or sharing contaminated needles, syringes, body piercing, or tattooing equipment).² Some untreated STIs in pregnant women can be transmitted vertically from the placenta to the womb or through the cervix during vaginal delivery.

Depending on the STI and specific health outcome, incubation and latency periods between infection, first symptoms and serious sequelae can be quite variable. For gonorrhea, the incubation period can be as short as one day after exposure,³ while the incubation period for syphilis can range from 1 week to 3 months.⁴ In acute HBV, the latency period can be relatively short, occurring within 4 to 24 weeks post exposure;⁵ whereas the latency period for an HPV infection to manifest into a precancerous lesion in the cervix may take as long as 10-20 years.⁶ In many cases, individuals can have an STI without any noticeable signs or symptoms of an infection. For instance, it is estimated that 10 percent of men and 5 to 30 percent of women with laboratory confirmed chlamydia develop symptoms;^7–9 In acute HBV and trichomoniasis infections, approximately 70 percent of men and women are asymptomatic.^{10, 11} Clinically undiagnosed or untreated STIs can progress to more serious health complications, such as pelvic inflammatory disease (PID), chronic pelvic pain, cancer, and infertility.¹² Mother-to-child transmission of STIs carry a significant risk of infant morbidity and mortality, including ectopic pregnancy, low birth weight, and premature birth, and stillbirth.¹³

Prevalence and Burden

According to the Centers for Disease Control and Prevention (CDC), there are more than 110 million cases of STIs in the United States¹³ and it is estimated that roughly 20 million new STI infections occur nationwide each year.¹³ An accelerating rise in rates of STI has been observed in the United States, with the most recent CDC surveillance data for the year 2018 showing the highest rates yet observed for combined cases of syphilis, gonorrhea, and chlamydia.¹⁴ Of particular concern, congenital syphilis cases increased 40 percent above the previous year, accompanied by a rise in the number of associated newborn deaths of which there were nearly one hundred. Access to STI screening and treatment programs and effective behavioral interventions are the health care system tools for reducing the burden of STI in the United States. Community programs and the social and political context also contribute to the STI epidemic and determine the resources available for addressing the complex needs of populations most at risk for STI.

Of patients presenting to STI clinics for testing, 17.5 percent of men who have sex with men (MSM) test positive for chlamydia and 26.5 percent test positive for gonorrhea. In men who have sex with women (MSW), 15 percent test positive for chlamydia and 14.6 percent test positive for gonorrhea. Finally, 11.5 percent of women presenting to STI clinics test positive for chlamydia and 7.4 percent test positive for gonorrhea.¹³ Although positivity rates are higher among individuals presenting at STI clinics, the majority of STI infections reported in the United States are diagnosed in other primary care settings.¹³ Along with the adverse physical, social, and psychological consequences, STIs create a steep economic burden for the United States’ healthcare system: $16 billion in direct health care costs each year, according to the CDC.¹⁵

Risk Factors

The unequal distribution and patterns of STI rates are influenced by physiology, behaviors, and importantly, by social and structural inequalities.^44–46 Unequal access to health care and limited resources for free or low cost clinical and public health programs to prevent STI contribute to differences in prevalence across subpopulations, as do historical and ongoing racial and ethnic disparities in the distribution of resources. Some communities and regions of the United States are at greater risk of STI based on the interaction of these and other factors. Individuals in sexual networks that have higher STI prevalence rates face a greater risk of exposure in each sexual encounter compared with those in lower prevalence sexual networks.⁴⁷ STI rates are highest in groups with less access to screening, diagnosis and treatment, more potential exposures (i.e., sexual partners), and lower use of protective interventions.

The terms female and male generally refer to the sex on one’s birth certificate and therefore seemingly gendered terms used in this report and in the studies reviewed may include cisgender, transgender and gender nonbinary people. Nevertheless, a person’s sex assigned at birth is an important determinant of sexual health outcomes. For instance, due to the asymptomatic nature of STIs, the female reproductive tract is uniquely vulnerable to the long-term complications of infection.³² In 2017, 1,127,651 cases of chlamydia were reported to the CDC among females (687.4 cases per 100,000 females), compared with 577,644 reported cases among males (363.1.5 cases per 100,000 males).¹³ Undiagnosed or untreated chlamydial infection in females can lead to PID, which can damage the fallopian tubes and increase the risk of infertility. It is estimated that tubal factor infertility accounts for 30 percent of female infertility in the United States, and much of this damage results from previous episodes of PID.³² Men can also be asymptomatic for both bacterial and viral STIs, which contributes to ongoing transmission in the absence of treatment. Uncircumcised males are at an increased risk for STIs. Randomized controlled trials (RCTs) conducted in sub-Saharan Africa found that male circumcision can reduce heterosexual HIV acquisition by 50 to 60 percent.^48–52 Additionally, male circumcision has been shown to decrease the risk of genital herpes and high-risk HPV infection.⁵³

Adolescents and young adults who are sexually active have higher rates of STIs, particularly chlamydia gonorrhea and HPV, compared with other age groups.¹³ Data from a recent systematic review by Falasinnu and colleagues reported that younger age was consistently associated with an increased risk of STIs.⁵⁴ Published incidence and prevalence estimates indicate that half of all new STIs occur in young people ages 15 to 24 years and one in four sexually active adolescent females has an STI.¹⁴ Risks of acquiring an STI are even higher among those who begin sexual activity earlier in adolescence, have multiple sexual partners (either concurrently or sequential sexual partners of limited duration), participate in other high-risk behaviors (such as alcohol or drug abuse), or live in detention facilities. Furthermore, adolescents may be more biologically susceptible to infection (for example, due to cervical ectopy in adolescent females) and may also lack adequate access to health care.^{13, 55} Stigma and shame, distrust in health care providers, and limited access to confidential reproductive health services for adolescent boys and girls and young adults, can also contribute to higher prevalence of infection since STI information, screening, treatment may be more difficult to obtain.

Higher rates of STIs are observed in certain racial and ethnic groups. For example, while rates of chlamydia have been increasing among all groups, rates of chlamydia among Black women and men in 2017 were 5 times and 6.6 times higher, respectively, than among White women and men.¹³ Likewise, in 2017, the rate of chlamydia in American Indians/Alaska Natives was 3.7 times higher; in Native Hawaiians/Pacific Islanders, 3.4 times higher; and in Hispanics, 1.9 times higher than in Whites. Asians had the lowest rate of chlamydia in 2017; the rate among Whites was 1.6 times higher than among Asians. It is thought that race and ethnicity may be surrogate markers for other social characteristics (such as income, employment, insurance coverage, and educational level) and interpersonal networks related to sexual activity or drug-use that are associated with increased STI risk.⁵⁶ Even without these disparities, it is also possible that factors such as fear and distrust of health care organizations, language barriers, and perceived or actual discrimination may impact decisions to seek medical care in certain racial or ethnic groups.¹³

Rates of STIs are higher among men who have sex with men (MSM), compared with rates in heterosexual women and men.¹³ For example, MSM accounted for over 68 percent of reported cases of primary and secondary syphilis during 2017, and this percentage has been increasing over time. Factors that may contribute to higher rates of STIs in MSM include the number of lifetime partners, the number of recent or current sex partners, frequency of engaging in sex without using condoms, and experiences of stigma or discrimination that may increase high risk sexual behavior or barriers to STI preventive care and treatment.¹³ MSM, WSW, and gender minorities such as transgender individuals can encounter challenges accessing non-judgmental health care and inclusive health education. Data on STI rates among transgender individuals are not collected at the national level and gender identity data are not routinely collected, therefore data on MSM likely include STI rates for transgender women. In the United States, the prevalence of HIV among transgender women is 27.7% among all transgender women and 56.3% among black transgender women.⁵⁷ Lifetime rates of other STIs in transgender women have been reported as 1.4% for P&S syphilis in Whites compared to 21.6% and 14.7% in Hispanics and Blacks, respectively. Rates of HBV infection are 6.5% among Whites compared to 36.0% in Hispanics and 35.5% in Blacks.⁵⁸ There are limited data on HIV prevalence in transgender men. One study reported that only 2% of a national sample of transgender men were HIV-infected; however, 91% had been diagnosed with an STI at some point in the past.⁵⁹

Intravenous drug users demonstrate greater risk for HIV and HBV. They are also at greater risk for other STIs if they engage in transactional sex or engage in sex while using drugs or alcohol. A recent review by Medina-Perucha and colleagues found six primary factors that were associated with higher risk of STIs in women using heroin or other drugs.⁶⁰ These factors included lack of condom use, engaging in transactional sex, experiencing sexual violence, sexual activity (e.g., greater number of sexual partners, frequency of sexual activity), type and characteristics of sexual partners (e.g., heterosexual women reported less casual sex compared with bisexual or lesbian women), and engaging in drug use with sex partners.

Additional subpopulations that have higher STI risk include: ¹ transgender men and women,¹ current or former inmates,⁶¹ people with a history of sexual assault and/or abuse,¹ and sex workers.⁶² Disproportionate rates of STIs among marginalized populations are closely tied to social and economic factors such as low economic status, insurance coverage, social stigma, and level of education, which limit access to healthcare services and hinder health literacy. Social barriers to prevention, such as intimate partner violence (IPV) and gender-based power imbalance, are also important predictors of STI.^{63, 64} Studies have shown that IPV, relationship power imbalances are associated with inconsistent condom use and subsequently higher STI risk.^{63, 65–68} Women and men experiencing partner abuse may be less likely to negotiate protected sex due to fear and power inequality within their relationships. Other risk factors for STIs include: commercial, survival or coerced sex;¹ high number of new or multiple sexual partners in recent months;⁶⁹ sex partner with concurrent partners;⁶⁹ sexual intercourse under the influence of mind-altering substances;¹ and sexual intercourse with a partner who has an STI or is at high risk for an STI.^{1, 54}

Individuals who continue to have sex with partners who have an STI, or their partners remain untreated are at greater risk of reinfection. The CDC STD Treatment Guidelines (2015)¹ recommend rescreening 3 months after treatment for chlamydia, gonorrhea, or trichomoniasis. Likewise, individuals who are diagnosed with syphilis should receive followup serologic syphilis testing. Unless prohibited by state laws or regulations, the CDC also recommends that health care providers offer STI Expedited Partner Therapy (EPT; also known as patient-delivered partner therapy) to patients who are diagnosed with a STI. EPT allows the patient to provide medications or prescriptions to their partners without requiring them to be examined by a medical provider. According to the CDC guidelines, there is substantial evidence that EPT results in decreased rates of reinfection of chlamydia (20% reduction of reinfection at followup) and gonorrhea (50% reduction).

High rates of STI in the United States and documented disparities arise from a host of factors beyond individual behaviors, as noted in the previous two sections. Nevertheless, individuals at risk that obtain health care might benefit from interventions aimed at increasing protective behaviors and providing support and skills for reducing potential STI exposure. Those most at risk for STI may require interventions that acknowledge and address the broader social context that frames their experience and needs.

Sexual Health History and Risk Assessment

Primary care physicians play a crucial role in evaluating a patient’s risk of contracting STIs. They can accomplish this during primary care visits by conducting an inclusive and comprehensive sexual health history, which assesses an individual’s sexual activity and related behaviors that increase their risk for developing an STI and becoming pregnant.^{70, 71} Key elements to a sexual health history include an individual’s sexual orientation; frequency of sexual activity and the number of partners; and type of sexual engagement (e.g., penile-vaginal intercourse, oral sex, anal sex).⁷⁰ These are often referred to as the Five P’s: partners, practices, prevention of pregnancy, protection from STIs, and past history of STIs.^{1, 70} Numerous national organizations, including the American Academy of Pediatrics,⁷² the Centers for Disease Control and Prevention (CDC),¹ the American Academy of Family Physicians (AAFP),⁷³ and the American College of Obstetrics and Gynecology (ACOG)^{74, 75} recommend that physicians periodically obtain a sexual history or sexual risk assessment and discuss risk reduction with all patients. Additionally, these organizations and others have developed sexual history-taking or sexual risk assessment tools that providers can utilize in primary care to enable comprehensive, nonjudgmental risk assessment and obtain more complete and accurate information from patients.^{71, 76}

Behavioral Counseling Interventions to Prevent STIs

After determining STI risk, clinicians can reduce a patient’s future risk of contracting an STI by providing or referring patients for behavioral counseling aimed at increasing their likelihood of engaging in safer sexual practices and reducing sexual risk behaviors. While the availability of biomedical interventions to reduce transmission of viral STI (e.g., HIV pre-exposure prophylaxis, hrHPV vaccination) and bacterial STI (expedited partner treatment with antibiotics) has increased, the emphasis of behavioral counseling is on supporting individual health protective behaviors such as increasing condom use and reducing sexual risk behaviors. Guidance from the CDC cautions that in order to be effective, prevention counseling must be done in a nonjudgmental and empathetic way that is suitable to the patient’s culture, gender identity, language, age, and gender of sexual partners.¹ As part of the prevention message, health care providers should educate patients on how to reduce their risk of STI transmission, including abstinence, correct and consistent condom use, and limiting the number of sex partners.^{1, 77} An interactive approach that is tailored to the patient’s personal risk has been shown to be effective, as well as behavioral counseling that utilizes personalized goal-setting, motivational interviewing, and client-centered counseling.¹ Motivational interviewing is a behavior change technique that is used to increase motivation and commitment to change, help patients identify the problematic behaviors that the individual is most willing and able to change, help patients feel a sense of agency for promoting their own health. The CDC maintains a website of interventions it considers effective for HIV risk-reduction, including over 25 behavioral interventions tailored for a variety of different populations.⁷⁸ They commonly include motivational and cognitive-behavioral elements such as skills development with role-play, communication or negotiation training, values clarification exercises, and problem-solving.

Current Clinical Practice and Recommendations of Others

In 2015 the CDC issued new prevention guidelines for STIs, recommending that all providers routinely obtain a sexual history from their patients and encourage risk-reduction strategies, including prevention counseling.¹ ACOG echoed this recommendation and encourages providers to discuss contraception and STI risks with both adolescent and adult patients.^{74, 75, 79} Similarly, the AAP recommends that pediatricians and other health care providers actively support and encourage the consistent and correct use of condoms with adolescent patients and promote communication between parents and adolescents regarding healthy sexual development and appropriate contraception use.⁷² NICE recommends that upon identifying patients at high-risk for contracting an STI, providers should have one-on-one structured discussions aimed at encouraging preventive behaviors to reduce their risk.⁸⁰ Among vulnerable adolescents, they recommend that when appropriate, health practitioners provide one-on-one counseling, which includes education on how to prevent and/or get tested for STIs. The Society of Adolescent Health and Medicine (SAHM) recommends that health care providers provide STI and HIV education, counseling, and services to all adolescents, and that these services are incorporated into well-adolescent and contraception visits. A list of recommendations from other organizations can be found in Appendix B Table 1.

Surveys examining STI counseling practices among physicians in the United States have shown varied results. A survey of 508 pediatricians found that only 28 percent offered sexual risk reduction guidance to more than three-quarters of the parents of their adolescent patients.⁸¹ Similarly, a recent retrospective, cross-sectional study of 1000 randomly selected adolescent well-child visits found that only 21.2 percent had a documented sexual history⁸² and another study utilizing patient chart reviews found that sexuality-related education was provided to fewer than 20 percent of adolescent patients.⁸³ Conversely, 88 percent of 541 Pennsylvania primary care physicians reported asking their adolescent and young adult patients (ages 15 to 25 years) about sexual activity; 80 percent reported counseling those patients about STI/HIV transmission and prevention.⁸⁴ In the same study, however, 70 percent of the clinicians believed STI counseling in general to be ineffective. Higher compliance was also reported in a recent survey of 1,154 practicing OB/GYNS, which found that 63 percent reported routinely asking patients about their sexual activity and history.⁸⁵ Primary care physicians frequently reported insufficient time as the main barrier to providing STI and/or HIV counseling during a patient visit.^{77, 86, 87} Other barriers reported include insufficient staff, lack of comfort discussing sexual health-related topics, and inadequate knowledge.^86–89

Previous USPSTF Recommendation

Identifying patients at risk for STIs and identifying effective behavioral interventions to reduce future infections is an important clinical step for primary and secondary preventive interventions in primary care. Screening and treatment are also important for secondary prevention of STIs, and the USPSTF provides several recommendations. For example, the USPSTF recommends early screening for syphilis infection in all pregnant women (A recommendation) as well as in nonpregnant adolescents and adults who are at increased risk for infection (A recommendation).^{90, 91} The USPSTF also recommends screening for chlamydia and gonorrhea in sexually active women aged 24 years and younger, as well as older women who are at increased risk for infection (B recommendations – currently being updated), but found insufficient evidence to recommend screening for chlamydia and gonorrhea screening in sexually active men. The USPSTF also recommends screening for hepatitis B infection in persons at high risk for infection (B recommendation).⁹² The USPSTF recommends against routine serologic screening for genital HSV in asymptomatic adolescents and adults, including those who are pregnant (D recommendation).⁹³ Finally, the USPSTF has previously concluded that there is insufficient evidence to recommend routine screening pelvic examinations for asymptomatic women who are not at increased risk for any specific gynecologic condition, including STIs (I recommendation).⁹⁴ An important opportunity to discuss sexual health risks and to recommend behavioral counseling interventions may occur when patients are identified for STI screening in primary care on the basis of existing USPSTF guidelines.

In 2014, the USPSTF recommended intensive behavioral counseling for all adolescents who are sexually active adolescents and for adults at an increased risk for sexually transmitted infections (B recommendation).⁹⁵ They found adequate evidence that intensive behavioral counseling interventions reduced the likelihood of STIs in sexually active adolescents and among adults at increased risk for STI.⁹⁵ Additionally, the USPSTF found adequate evidence that intensive interventions reduced risky sexual behaviors and increased the likelihood of condom use and other protective sexual practices. They found adequate evidence that the harms of behavioral interventions to reduce the likelihood of STIs were small at most, with the primary harm being the opportunity cost associated with intensive behavioral counseling.⁹⁵ The USPSTF concluded with moderate certainty that intensive behavioral counseling interventions reduce the likelihood of STIs in sexually active adolescents and in adults who are at an increased risk, resulting in a moderate net benefit.