More than two million cases of chlamydia, gonorrhea and syphilis were reported in the United States in 2016, the highest number ever, according to the annual Sexually Transmitted Disease Surveillance Report released today by the Centers for Disease Control and Prevention (CDC).

The majority of these new diagnoses (1.6 million) were cases of chlamydia. There were also 470,000 gonorrhea cases and almost 28,000 cases of primary and secondary syphilis – the most infectious stages of the disease. While all three of these STDs can be cured with antibiotics, if left undiagnosed and untreated, they can have serious health consequences, including infertility, life-threatening ectopic pregnancy, stillbirth in infants, and increased risk for HIV transmission.

“Increases in STDs are a clear warning of a growing threat,” said Dr. Jonathan Mermin, director of CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention. “STDs are a persistent enemy, growing in number, and outpacing our ability to respond.”

Epidemic accelerating in multiple populations—impact growing in women, infants, and gay and bisexual men

While young women continue to bear the greatest burden of chlamydia (nearly half of all diagnosed infections), surges in syphilis and gonorrhea are increasingly affecting new populations.

Syphilis rates increased by nearly 18 percent overall from 2015 to 2016. The majority of these cases occur among men – especially gay, bisexual and other men who have sex with men (MSM) – however, there was a 36 percent increase in rates of syphilis among women, and a 28 percent increase in syphilis among newborns (congenital syphilis) during this period.

MSM bear a great syphilis burden. MSM make up a majority of syphilis cases, and half of MSM diagnosed with syphilis were also living with HIV – pointing to the need to integrate STD and HIV prevention and care services.