CHICAGO (Reuters) - New U.S. cases of three common sexually transmitted diseases - chlamydia, gonorrhea and syphilis - reached more than 2 million in 2016, a new record, U.S. health officials said, prompting calls for more effective prevention efforts.

Most of the new diagnoses were cases of chlamydia, which comprised 1.6 million cases. But there were also nearly a half million (470,000) new gonorrhea cases and nearly 28,000 new cases of syphilis, according to an annual report issued by the Centers for Disease Control and Prevention on Tuesday.

All three sexually transmitted diseases can be cured with antibiotics, but if left undiagnosed, they can cause serious health problems, 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,” Dr. Jonathan Mermin, director of CDC’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.”

According to the Sexually Transmitted Disease Surveillance Report, there were 27,814 newly reported cases of syphilis in 2016, up nearly 18 percent from 2015. Most of these cases - 80.6 percent - occurred in men who have sex with men, but rates among women rose 36 percent, and rates among newborns rose 28 percent.

Gail Bolan, director of CDC’s Division of STD Prevention, called the increase in syphilis rates among babies “a tragic systems failure.”

“All it takes is a simple STD test and antibiotic treatment to prevent this enormous heartache and help assure a healthy start for the next generation of Americans,” Bolan said in a statement.

Rates of gonorrhea, a disease increasingly becoming resistant to antibiotics, rose 22.2 percent among men and 13.8 percent among women in 2016 compared with the prior year.

To reverse these trends, CDC is calling on state and local health departments to refocus efforts in investigating these diseases and improving rapid testing and treatment capabilities. The CDC also recommends that providers make STD screening a standard part of medical care.