David Harvey, executive director of the National Coalition of STD Directors, called the situation "out of control".
Officials are working on new approaches to the problem, such as home-test kits for some STDs that will make it easier for people to learn they are infected and to take steps to prevent spreading it to others, Mena said.
Another expert said a core part of any effort must work to increase the use of condoms.
"It's pretty simple. More sexually transmitted infections occur when people are having more unprotected sex," said Dr Mike Saag, an infectious disease expert at the University of Alabama at Birmingham.
Syphilis is a bacterial disease that surfaces as genital sores but can ultimately lead to severe symptoms and death if left untreated.
New syphilis infections plummeted in the US starting in the 1940s when antibiotics became widely available. They fell to their lowest ever by 1998, when fewer than 7000 new cases were reported nationwide. The CDC was so encouraged by the progress it launched a plan to eliminate syphilis in the US.
But by 2002 cases began rising again, largely among gay and bisexual men, and they kept going. In late 2013, CDC ended its elimination campaign in the face of limited funding and escalating cases, which that year surpassed 17,000.
By 2020 cases had reached nearly 41,700 and they spiked even further last year, to more than 52,000.
The rate of cases has been rising, too, hitting about 16 per 100,000 people last year. That's the highest in three decades.
Rates are highest in men who have sex with men, and among Black and Hispanic Americans and Native Americans. While the rate for women is lower than it is for men, officials noted that it's has been rising more dramatically - up about 50 per cent last year.
That ties to another problem - the rise in congenital syphilis, in which infected moms pass the virus on to their babies, potentially leading to death of the child or health problems like deafness and blindness. Annual congenital syphilis cases numbered only about 300 a decade ago; they surged to nearly 2700 last year. Of last year's tally, 211 were stillbirths or infant deaths, Mena said.
The increases in syphilis and other STDs may have several causes, experts say. Testing and prevention efforts have been hobbled by years of inadequate funding, and spread may have gotten worse - especially during the pandemic - as a result of delayed diagnosis and treatment. Drug and alcohol use may have contributed to risky sexual behavior. Condom use has been declining.
And there may have been a surge in sexual activity as people emerged from Covid-19 lockdowns. "People are feeling liberated," Saag said.
The arrival of monkeypox added a large additional burden. CDC recently sent a letter to state and local health departments saying that their HIV and STD resources could be used to fight the monkeypox outbreak. But some experts say the government needs to provide more funding for STD work, not divert it.
Harvey's group and some other public health organisations are pushing a proposal for more federal funding, including at least $500 million for STD clinics.
Mena, who last year became director of the CDC's Division of STD Prevention, called for reducing stigma, broadening screening and treatment services, and supporting the development and accessibility of at-home testing. "I envision one day where getting tested (for STDs) can be as simple and as affordable as doing a home pregnancy test," he said.
