A spike in potentially deadly syphilis infections in fetuses and infants represents a massive failure of prevention and prenatal care in the United States, reflecting racial and geographic health-care disparities across the country.

The number of congenital syphilis cases increased by 261 percent between 2013 and 2018, the Centers for Disease Control and Prevention (CDC) reported Thursday, in a finding that alarmed sexual health experts. Congenital syphilis, in which a fetus or infant acquires the sexually transmitted infection (STI) during pregnancy, can cause miscarriage, stillbirth, early infant death, and lifelong physical and neurological problems.

Congenital syphilis is preventable, as long as the pregnant person’s syphilis is diagnosed and adequately treated during pregnancy. But that hasn’t stopped the numbers from rising dramatically, particularly in Black and Latinx communities. In 2018, there were 1,306 congenital syphilis cases in the United States, up from 362 in 2013. The CDC found that 94 cases in 2018 resulted in stillbirth or early infant death.

Congenital syphilis “serves as a prism for health inequities” in the United States, said Dr. Christopher Hall, clinical advisory chair for the National Coalition of STD Directors.

“It’s greater in the South and the West, where we see women who have more limited access to prenatal care and appropriate therapies,” Dr. Hall told Rewire.News. Data from the CDC study backs that up. Fifty-three percent and 36 percent of 2018’s congenital syphilis cases were in the South and the West, respectively, compared to just 8 percent in the Midwest and 4 percent in the Northeast.

And like most STIs, congenital syphilis disproportionately affects communities of color—39 percent of infants with the infection were born to non-Hispanic Black women; 32 percent to Hispanic women; and 22 percent to non-Hispanic white women, according to the CDC.

Syphilis is caused by a bacteria, and the infection’s primary and secondary stages are marked by sores, rashes, and flu-like symptoms. If not treated, syphilis can go on to damage the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints. It’s one of the oldest STIs—it was recorded as early as the 1400s—though infection rates in the United States were so low by the late 1990s that public health experts believed they could eliminate the disease entirely.

But syphilis has roared back, with cases rising consistently for the past two decades. Though men, particularly men who have sex with men, account for most syphilis cases, the rate of primary and secondary stage syphilis for women increased by 173 percent between 2014 and 2018.

The CDC recommends pregnant people be screened for syphilis at their first prenatal visit, and that those at high risk be screened again at 28 weeks, and a third time at delivery. Those who test positive are treated with penicillin, and infant infection can be avoided if an antibiotic regimen is started at least 30 days before delivery.

That means every case of congenital syphilis essentially represents a failure to diagnose or treat a pregnant person. The CDC study was designed to identify the missed opportunities that led to that disturbing failure. There were many.

In 28 percent of cases, the women didn’t receive timely prenatal care. There are many barriers to prenatal care, including a lack of health insurance and a lack of available and accessible providers, especially in rural areas. Other vulnerabilities such as homelessness and substance abuse can prevent people from getting the care they need during pregnancy.

But even when pregnant people were tested and diagnosed in time, many failed to receive adequate treatment. Dr. Anne Kimball, the lead author on the study, explained that syphilis is treated with intramuscular shots of penicillin. Pregnant people diagnosed with primary and secondary stage syphilis need just one injection. For those diagnosed with late latent syphilis, treatment requires three shots given seven days apart.

If a patient misses one of these shots by more than a few days, they must start the series again. And the completed series must begin more than 30 days from delivery, Dr. Hall said.

“The lives of many of the women most at risk for syphilis during pregnancy are chaotic, so getting them to clinic three times is not easy,” he said. The timing of treatment is also complicated by the fact that untreated syphilis often leads to premature birth, and it is difficult to accurately predict delivery dates.

In 9 percent of cases, the pregnant person received prenatal care without being tested for the STI, according to the CDC study. Pregnant people were categorized as having received prenatal care even if they had just one visit prior to delivery, Dr. Kimball said, which could explain the lack of testing.

“This is why we recommend syphilis testing the first time a woman seeks prenatal care,” she said.

This finding, Dr. Kimball said, points to a need for additional provider education, as many providers were trained in an era when congenital syphilis was not an issue.

Eleven percent of cases in the CDC study involved pregnant people whose syphilis was diagnosed too late in the pregnancy to complete treatment. These infants are treated as soon as they are born, but treatment can be complicated and expose infants to invasive tests and procedures like X-rays, spinal taps, and IV antibiotics, Dr. Hall told Rewire.News.

The good news is that we know how to prevent congenital syphilis and the infant mortality it causes. But closing the gaps in care will require concerted efforts to expand prevention, increase testing for people before and during pregnancy, and improve access to prenatal care across the country for people of all socioeconomic backgrounds.

“In order to prevent babies from getting syphilis we have to identify and treat infections in moms, but we also have to prevent those women from becoming infected in the first place,” Dr. Kimball said. “There’s an important role for primary prevention in adults.”

Correction: A previous version of this article incorrectly attributed a quote to Dr. Christopher Hall.