The number of Americans diagnosed with chlamydia, gonorrhea or syphilis reached a record high in 2016 for the second year in a row, with more than 2 million cases reported, according to recently released federal data.

Cases of these three sexually transmitted diseases have been increasing since 2014, reversing a downward trend that began in 2006. Health officials say the rates reflect decreasing condom usage, a lack of awareness about STDs among doctors and patients and a falling number of STD clinics.

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

As the number of women with syphilis has jumped, so has the number of babies born with syphilis passed down from their mothers. Congenital syphilis, as it is known, can cause still births or permanent disabilities. Since 2012, the number of babies born with congenital syphilis nationwide nearly doubled, reaching 632 last year.

Chlamydia, gonorrhea and syphilis are curable, but if left untreated they can cause infertility or other serious health problems. People may not get tested because they don’t have symptoms or don’t notice their symptoms, but then are still spreading the disease to others.

Dr. Gail Bolan, director of the CDC’s division of STD prevention, said the increase in gonorrhea rates in 2016 was of particular concern as more strains become resistant to antibiotics. There were once several antibiotics that could cure the infection, but the bacteria have mutated and now it is harder to treat.

“We’re down to our last class of antibiotics that we have available to treat gonorrhea,” Bolan said. “In the past, we just moved on to the next class of antibiotics, but we’re now on the edge. … We want to make sure we keep the threat of these potentially resistant strains at a low level.”