The Centers for Disease Control and Prevention (CDC) estimates indicate about 20 percent of the U.S. population – approximately one in five people in the U.S. – had an STI on any given day in 2018, and STIs acquired that year will cost the American healthcare system nearly $16 billion in healthcare costs alone. Because many cases of STDs go undiagnosed—and some common viral infections, such as human papillomavirus (HPV) and genital herpes, are not reported to CDC at all—the reported cases of chlamydia, gonorrhea, and syphilis represent only a fraction of the true burden of STDs in the United States. Untreated STDs can lead to serious long-term health consequences, especially for adolescent girls and young women, such as infertility. Chlamydia, the most frequently reported bacterial sexually transmitted disease in the United States, is caused by the bacterium, Chlamydia trachomatis. Under-reporting of chlamydia is substantial because most people with chlamydia are not aware of their infections and do not seek testing.