These STDs Are the Most Common Infectious Diseases Reported to the CDC

Sexually transmitted disease diagnoses in 2018 broke a record for the fifth consecutive year, according to new data from the U.S. Centers for Disease Control and Prevention (CDC).

Chlamydia was the most common STD in 2018, with more than 1.7 million cases reported, followed by more than 580,000 cases of gonorrhea—3% and 5% increases over 2017, respectively. Though less common, syphilis diagnoses also rose, topping 115,000 cases in total, according to the CDC.

“These are just infections that were diagnosed and reported,” says Elizabeth Torrone, an epidemiologist at the CDC. Since lots of STDs are asymptomatic, “many people have infections that never get diagnosed and reported. This really just gives us the minimum burden of the STD epidemic.”

The report says chlamydia and gonorrhea also topped the CDC’s most recent list of “nationally notifiable” illnesses, a collection of about 120 infectious diseases and other conditions that local health departments report to the CDC. (Full 2018 data is not yet available; 2017 is the latest year on record.) Other common STDs, like HPV, are not considered nationally notifiable.

Torrone says she’s particularly worried about the rise in syphilis, both among adults and babies who contract the infection from their mothers during pregnancy or delivery. About 1,300 cases of congenital syphilis were reported in 2018, a 40% increase over the year before, and the disease contributed to 94 infant deaths.

“All of those cases of congenital syphilis, including those deaths, could have been prevented,” Torrone says, if the mothers had been treated during pregnancy. The CDC advises all pregnant women to undergo screening for syphilis and other STDs to prevent transmission to their children.

There are a few possible reasons for persistent increases in STD diagnoses, Torrone says. One could simply be that more people are getting screened, thus leading to more case reports to the CDC. But Torrone says research also suggests fewer people are using condoms, particularly in high-risk populations such as young adults and men who have sex with men. And certain diseases that previously impacted subsets of the national population seem to have spread to new groups, which makes it harder to prevent and contain infections. For example, syphilis historically affected primarily men who have sex with men, but is now also on the rise among women.

The CDC is working on these issues at the public-health level, but Torrone emphasizes that individuals should also do their part by using condoms properly, getting tested regularly and talking about sexual health with their partners and health care providers. “We need to take action to break the cycle of increases,” Torrone says.