People stand in line to receive the monkeypox vaccine at San Francisco General Hospital.

A man who recently sought care for monkeypox at Stanford did not report sexual contact or lesions on the anus or genitals — an unusual case that highlights the need to better understand how the virus may be spreading beyond sexual networks.

The man’s case was documented in a research letter published Tuesday by Stanford researchers in the Emerging Infectious Diseases journal.

The man had recently traveled to the United States from the United Kingdom, and his highest-risk exposure was attending a crowded outdoor event, where he had close contact with others, including dancing, for a few hours, researchers said. He did not come into contact with anyone who appeared sick, or who had visible lesions. It was not an event attended specifically or mostly by gay and bisexual people, the letter said.

“His case highlights the potential for spread at such gatherings, which may have implications for epidemic control,” it said.

Dr. Abraar Karan, an infectious disease researcher at Stanford and the letter’s lead author, characterized the report as just one case, and a “rare event,” since there have been very few cases documented outside of sexual networks in the current outbreak.

The patient’s first lesion appeared about 14 days after the event, and he also attended other similar outdoor events over several days. Lesions were found on his hands, lip, torso and back.

Researchers did not provide the date the man’s case was first confirmed, citing privacy reasons, but it was several weeks ago.

Researchers were not able to pinpoint the exact route of transmission, just that it was not a high-risk sexual exposure. It may have been from skin-to-skin contact, touching surfaces, or respiratory droplets. These are all known modes of transmission from previous outbreaks of monkeypox, which is endemic in central and western Africa and in 2003 resulted in an outbreak in the Midwest, with 47 cases that were traced to pet prairie dogs imported from Ghana.

Contact aside from sexual intimacy is an infrequent way for monkeypox to spread in the context of the current global outbreak. The vast majority of cases have been transmitted though sexual networks, mostly among men who have sex with men. In the United States, more than 90% of cases are in this community, according to analysis of the cases where demographic information was available, said the Centers for Disease Control and Prevention. In total, about 12,600 cases in all have been documented in the United States.

Researchers emphasized that one single case report should not prompt major changes in the public health response to the outbreak, but that it is interesting because it shows there are multiple ways the virus can spread.

“This should not be a cause for concern in the sense that this remains a very rare event we haven’t documented in the medical literature in this outbreak, aside from just a few times,” said Karan. “The overwhelming majority of transmission is still through high-risk sexual networks and high-risk sexual exposure. This should be taken as a case report. That’s all it is.”

Catherine Ho (she/her) is a San Francisco Chronicle staff writer. Email: cho@sfchronicle.com Twitter: @Cat_Ho

Catherine Ho covers health care at The San Francisco Chronicle. Before joining the paper in 2017, she worked at The Washington Post, the Los Angeles Times and the Daily Journal, writing about business, politics, lobbying and legal affairs. She's a Bay Area native and alum of UC Berkeley and the Daily Californian.