Chapter 122: Chlamydia and Other Sexually Transmitted Infections

INTRODUCTION

Three hundred and seventy-six million new cases of the four curable (chlamydia, gonorrhea, syphilis, and trichomoniasis) sexually transmitted infections (STIs) are estimated to occur each year, according to the World Health Organization (WHO).¹ This amounts to more than 1 million curable STIs occurring each day. The burden of viral STIs is similarly high, with an estimated 417 million prevalent cases of herpes simples virus infection (HSV) and approximately 291 million women infected with human papillomavirus (HPV).¹ In contrast to these infections, many countries have achieved successful control of other STIs like chancroid (etiologic agent Haemophilus ducreyi) and lymphogranuloma venereum or LGV (etiologic agent Chlamydia trachomatis serovars L1, L2, and L3).¹ In 2016, WHO released the “Global health sector strategy on sexually transmitted infections 2016-2021,” with a goal of ending STI epidemics as a major public health concern.² This strategy outlined several guiding principles including: achieving universal health coverage; use of evidence-based interventions and policies; promoting human rights, gender equality, and health equality; working through partnerships; integration across relevant sectors; and engagement and empowerment of people most affected. With this in mind, several goals to be achieved by 2030 include: ≤50 cases of congenital syphilis per 100,000 live births in 80% of countries; 90% reduction in T. pallidum incidence globally; 90% reduction in N. gonorrhoeae incidence globally; and 90% national vaccination coverage and at least 80% district coverage in countries with HPV vaccine in their national immunization program.²

Chlamydia, gonorrhea, and syphilis ranked first, second, and third among infectious diseases reportable to the U.S. National Notifiable Diseases Surveillance System in 2017, with chlamydia and gonorrhea alone accounting for 95% of these cases.³ For nonreportable diseases such as trichomoniasis and HPV, data collection is less complete. However, estimates from alternate sources suggest that both of these diseases are even more common than chlamydia.⁴ Data from 2008 estimated that 81 million Americans were living with a chronic viral STI, excluding human immunodeficiency virus (HIV).⁴ Because many STIs are asymptomatic and go undiagnosed, current surveillance systems probably underestimate the actual burden of disease. In truth, the prevalence of STIs in the United States is largely unknown. However, STIs are unquestionably a substantial health and economic burden.

In 2013, the U.S. Centers for Disease Control and Prevention (CDC) estimated 20 million new STIs each year, including HIV, hepatitis B, HSV type 2, syphilis, gonorrhea, trichomoniasis, chlamydia, and HPV.⁵ The economic burden of STIs is substantial, with direct medical costs estimated at 15.6 billion annually in 2008 (in year 2010 U.S. dollars).⁵ These estimates do not account for indirect costs from productivity losses (lost wages) or intangible costs from pain, suffering, or diminished quality of life. Although adolescents and young adults aged 15–24 years constitute only 25% of the sexually active population, they represent over half of new STI cases, contributing disproportionately to the total economic burden of STIs. ...