Health officials say syphilis has reached its highest level since 1995 with the increase all in men.
Syphilis remains far less common in the U.S. than many other sexually spread diseases. But there has been a steady rise in gay and bisexual men catching the disease. They account for most of the recent infectious cases.
Since 2005, the rate in men has nearly doubled. It is much lower in women and hasn't changed much.
Syphilis is a potentially deadly bacterial disease that surfaces as genital sores. It was far more common until antibiotics became available in the 1940s, slashing the number of annual cases to below 6,000.
Last year, there were nearly 17,000 cases.
The Centers for Disease Control and Prevention released the numbers Thursday.
Explore further: Two sex-spread diseases increase, syphilis down
CDC report: www.cdc.gov/mmwr