State health officials say Colorado saw a major increase in syphilis cases between 2018 and 2023, especially congenital syphilis,which is when infection passes from mother to baby during pregnancy.
“Like other sexually transmitted infections, the risk is going to occur when individuals are having sex,” Colorado Department of Public Health & Environment state epidemiologist Dr. Rachel Herlihy said.
The Colorado Department of Public Health and Environment says congenital syphilis cases increased more than seven times over a five-year period prompting the state to declare an epidemic in 2024. During that time, Governor Jared Polis called the yearslong trend a “real danger” for Colorado newborns.
“I think certainly having sex with multiple partners, or having sex with partners that you don't know, is going to be some of the increased risk factors for the infection,” Dr. Rachel Herlihy said.
Dr. Herlihy told Denver7 limited access to healthcare, especially prenatal care, is a major risk factor for syphilis and congenital syphilis because it can prevent people from receiving important screening tests and treatment during pregnancy. Other factors linked to rising syphilis cases include inconsistent syphilis testing by providers, substance use, and homelessness.
“People weren't routinely being tested for syphilis. So, if you would get a screening test done for sexually transmitted infections, most likely you would be tested for chlamydia and gonorrhea, maybe HIV, but syphilis wasn't as commonly being tested for. That's one of the messages that we've been emphasizing with healthcare providers in the last few years, is the importance of also testing patients for syphilis,” Dr. Herlihy said.
But now, the state is seeing a shift and finding out why.
Provisional data shows the state recorded 64 congenital syphilis cases in 2024 compared to 44 in 2025. Overall cases also appear to be trending down from more than 3,200 cases in 2024 to 2,400 cases last year.
“We're obviously being cautiously optimistic that things are trending in the right direction. We would love to see a continued downward trend,” Dr. Herlihy said.
State epidemiologists told Denver7 increased testing may have temporarily boosted reported cases in 2024,
“One of the things that can happen when you put this emphasis on increased screening and increased testing is a temporary increase in the number of cases. That may have occurred in 2024, but 2025 numbers have come down, and that is a good sign for us,” Dr. Herlihy said.
Officials are hopeful the latest numbers show those interventions are starting to work.
“One of the things that we put in place in Colorado in 2024 was this really significant emphasis on increasing screening and then increasing treatment for individuals that screen positive. Those two actions have been really important for us to try and stabilize and ultimately decrease the number of syphilis and congenital syphilis cases that we're seeing,” Dr. Herlihy said.
State health officials said early testing during pregnancy is critical because syphilis is treatable with antibiotics when caught early.
“If treatment does not occur, the baby can be born with what's called congenital syphilis, and that can be a variety of symptoms, including cognitive issues, neurologic issues, and bone deformities. A lot of really severe manifestations of that infection can occur,” Dr. Herlihy added.
