STDs are having a comeback in the US, according to the latest Centers for Disease Control’s (CDC) data, published on Nov. 17. Syphilis, gonorrhea and chlamydia, in particular, have seen a dramatic increase between 2013 and 2014 that can’t be explained by an increase in screenings. Usually, these diseases can be resolved with simple treatment programs over a few days or weeks. But if they’re left undiagnosed or untreated, they can eventually lead to serious complications, ranging from infertility (gonorrhea), to arthritis (chlamydia), and even death (syphilis).
In 2014, 1.4 million new cases of chlamydia were reported to the CDC by local health department across the US, a 2.8% increase over the previous year. This is the highest number of new cases of a disease ever reported to the CDC.
Interestingly, the reported cases represent only a fraction of the actual number of STD cases. There’s an estimated 20 million new cases per year, most of which often go undiagnosed. At 456.1 cases per 100,000 people, chlamydia is by far the most common STD in the US—though not the fastest growing. That would be syphilis (6.3 cases per 100,000 people), which has witnessed an exponential growth, with an increase of 15.1% from 2013:
Similarly, the cases of gonorrhea (110.7 per 100,000 people), have gone up 5.1% from 2013.
Traditionally STDs affect primarily younger people under 24 (54% reported cases of gonorrhea and 66% of chlamydia) and, except for syphilis, are prevalent amongst women. The recent increases, though, are due primarily to new male cases.
This is especially true of gay and bisexual men, who aren’t only more affected by syphilis but ”are experiencing similar increases in gonorrhea and chlamydia infections” a CDC spokesperson told Quartz in a written statement, “underscoring the need to further understand what is contributing to the rise.”