Here's a gripping conversation starter to bring up over your family's Thanksgiving feast this year: Health officials in Michigan have identified an alarming cluster of syphilis infections in women's eyes.

The first-of-its-kind cluster—in five women all linked to one infected man—raises the possibility that a new strain of syphilis bacteria has adapted to more easily cause systemic syphilis, particularly disease that affects the eyes and central nervous system. A report of the cluster and what it might mean is published today by Michigan health officials in the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Eye syphilis, aka ocular syphilis, is not new. Syphilis bacteria, Treponema pallidum (formerly Spirochaeta pallida) are known to be able to spread to the eye, as well as the inner ear, and central nervous system when the sexually transmitted infection is left untreated. This spread can lead to blindness, deafness, and life-threatening neurosyphilis if it remains untreated.

But ocular syphilis is rare. It's only found in about 1 percent of syphilis cases, similar to inner ear and neurosyphilis, according to a large analysis published last year. When ocular syphilis does develop, it's most often seen in people who have late-stage syphilis, people who are 65 years of age or older, people who report injection drug use, and those who are HIV-positive.

But, in this cluster, the five women all had early-stage infections. They were all between 40 and 60 years old, and none reported injection drug use. This ocular syphilis cluster is also the first one documented as being linked by heterosexual transmission.

Cluster cases

The string of cases began to unravel in March 2022, when the first woman, Patient A, was referred to the Kalamazoo County Health and Community Services Department (KCHCSD) by an ophthalmologist. The woman reported blurry vision, fear of blindness, and genital lesions. Testing indicated syphilis, and she reported only one sex partner in the past 12 months—a man she met online. Within a few days, the state health department reached out to the man but was rebuffed.

Weeks later, in April 2022, Patient B was admitted to a hospital with neurosyphilis. An ophthalmologist had identified cranial nerve abnormalities and had sent her to the emergency department. There, she reported headache, mild hearing loss, blurry vision, and double vision. She named the same recent sex partner reported by Patient A, saying she, too, met him online.

In May 2022, Patient C was reported to a local health department in southwest Michigan. She had a full-body rash, floaters in her eyes, sensitivity to light, and cranial nerve abnormalities. She again reported the same partner as Patient A and B and said she had met him online.

Patient D was diagnosed with ocular syphilis in June 2022, again naming the same partner. And in July 2022, Patient E was admitted to the hospital with ocular syphilis and neurosyphilis, again naming the same partner as the other cases.

From March to May, state health officials reached out to the common male sex partner multiple times. But, he provided little information, said he had left the state, and was a no-show for a scheduled medical appointment in April. In May, after Patient C was identified, a public health doctor looked up the man's electronic medical records, discovering that in January of 2022 he had gone to a hospital emergency department for ulcerative genital and anal lesions. At the time, he was treated for a presumed herpes infection—but his herpes test was negative and he was not tested for syphilis.

Public health implications

Also in May, a state disease intervention specialist was able to renew contact with the man, and he showed up for an appointment at KCHCSD. In the appointment, doctors noted that the man had no signs of syphilis, no vision problems, nor hearing impairment. Laboratory testing confirmed he had early latent syphilis, a stage of the disease that occurs within a year of an initial infection when symptoms appear to resolve but the disease is still present. The man reported having multiple sex partners in the previous year but declined to disclose their identities.

Patient B through E also reported having other sex partners. Of those who were identified, health officials reported negative syphilis tests for them. Patient E did not identify her other partners, and officials were not able to contact them.

Given the odd nature of this cluster, health officials in Michigan speculated that the man may have been infected with a strain of T. pallidum that is more prone to causing ocular and neurosyphilis than others. But, they weren't able to identify the strain. Genetic testing for syphilis works best when there are primary ulcers or moist lesions from which bacteria can be swabbed. Only patient A had primary stage syphilis with genital lesions at the time of diagnosis.

All the women and the man were treated for their infections and, since then, no other cases in Michigan have linked back to anyone in the cluster. The fact makes health officials hopeful they've stopped the spread of this nefarious, unidentified T. pallidum strain, but it's impossible to know without wider surveillance and identification of all sex partners.

Even without a new worrisome strain of T. pallidum around, the state of sexually transmitted infections in the US is dire. Rates of STIs, including syphilis, chlamydia, and gonorrhea, have been skyrocketing for years. In a report earlier this year, the CDC noted that national cases of syphilis increased 74 percent from 2017 to 2021. In 2022, the number of babies born with syphilis was more than 10 times the number in 2012.