Scottsdale, Arizona - Sexually transmitted infections (STI) have increased in the U.S. for the third year in a row, according to a new report by the Centers for Disease Control and Prevention (CDC). The 2016 Sexually Transmitted Disease Surveillance Report shows more than 2 million cases of chlamydia, gonorrhea and syphilis were reported in the U.S.– the highest number ever.

"Worsening trends are always concerning," says, Dr. Stacey Rizza, Mayo Clinic infectious diseases specialist. "This is a public health issue. More infections mean more transmissions. We need better screening for STIs, better education to the public to use barrier protection, and need people get checked for STIs and then to get treated."

“STIs can cause a number of health issues including infertility, pelvic inflammatory disease, congenital abnormalities to unborn fetuses, urethritis and orchitis," says Dr. Rizza

Sexually transmitted bacterial and parasitic infections including including gonorrhea, syphilis and chlamydia are commonly treated with antibiotics. "Antibiotics may help once the infection has been diagnosed, but are of no use if people don’t get checked, or already have damage done before being diagnosed and treated," says Dr. Rizza. "Unfortunately, some STIs have growing antibiotic resistance."

Gonorrhea has grown increasingly resistant to antibiotics used to treat it–a result of misuse and overuse of antibiotics.

The CDC estimates there are 20 million new STIs in the U.S. each year, and half are among people ages 15 to 24.