CDC reports unique ocular syphilis cluster caused by an unknown strain

Syphilis bacteria

Syphilis bacteria

US Centers for Disease Control and Prevention (CDC) researchers report the first known cluster of ocular syphilis cases linked to a common heterosexual partner, which they say suggests the presence of an unidentified causative bacterial strain with increased risk for systemic complications.

The cluster, identified in southwest Michigan in March to July 2022, was described late last week in Morbidity and Mortality Weekly Report. Treponema pallidum is a spirochete bacterium that causes syphilis, a sexually transmitted infection (STI) that's been on the rise in the United States and other countries.

Untreated syphilis can lead to ocular syphilis, otosyphilis, and neurosyphilis from T pallidum infection of the eye, inner ear, or central nervous system, respectively, the study authors said.

Case investigation, health advisory

The cluster involved five 40- to 60-year-old women who had the same male partner, with whom they engaged in vaginal (100%), oral (40%), and anal (40%) sex. None of the women were HIV-positive or reported drug use or transactional sex. All were diagnosed as having early-stage syphilis, hospitalized, and treated with intravenous (IV) penicillin. They reported a range of ocular, dermatologic, neurologic, and otic symptoms.

The man involved was diagnosed as having early latent syphilis without ocular involvement. A medical records search revealed that he had sought care for ulcerative penile and anal lesions in January 2022 and was prescribed the antiviral drug acyclovir. He reported no male or transgender sexual contact. After his syphilis diagnosis, he received IV penicillin.

State officials launched a case investigation, notified sex partners, and referred patients to a public health clinic for diagnosis and treatment, hospital care coordination, and sample collection.

They also sent a health advisory to healthcare providers and surrounding counties through the Michigan Health Alert Network on the ocular syphilis cases to date; the signs and symptoms of ocular syphilis, otosyphilis, and neurosyphilis; recommendations for obtaining sexual histories, performing examinations, reporting cases to public health, and consultation with specialists; and recommended treatments.

In June, the Kalamazoo County Health and Community Services Department, the Michigan Department of Health & Human Services, and the New York City STD [sexually transmitted diseases]/HIV Training and Prevention Center held a training webinar on syphilis diagnosis and treatment and the Michigan ocular syphilis cluster for county health department nurses, physicians, and STI staff across Michigan.

A sixth patient diagnosed as having secondary syphilis with ocular and otic involvement was considered unrelated to the cluster because no sexual link to any of the other cases was established.

Strain remains unidentified

While the researchers say the case suggests an unidentified T pallidum strain tied to higher risk for systemic involvement, the lack of genetic material in the specimens precluded molecular typing.

"No shared host susceptibility characteristics were identified among patients in this cluster," they wrote. "In addition, no disease transmission linked to the cluster was identified after treatment of the male sex partner, and no ocular syphilis patients with sexual linkage to others who also developed ocular syphilis have since been identified in Michigan."

An immediate ophthalmologic evaluation should be facilitated for persons with syphilis and ocular complaints.

Those observations, they said, suggest that the T pallidum strain may have stopped circulating after all were treated. "However, without cluster-specific or wider geographic T. pallidum molecular typing surveillance, this hypothesis cannot be confirmed," they wrote

"A high index of clinical suspicion and thorough sexual history are critical to diagnosing ocular syphilis, otosyphilis, and neurosyphilis," they wrote. "Coordination of disease surveillance with disease intervention specialist investigation and treatment referral can interrupt syphilis transmission."

Likewise, early diagnosis and treatment of syphilis can prevent systemic complications, including permanent vision or hearing loss. "An immediate ophthalmologic evaluation should be facilitated for persons with syphilis and ocular complaints," they concluded. "Any cranial nerve dysfunction should prompt a lumbar puncture and cerebrospinal fluid evaluation before treatment, if possible."

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