Rare Mpox Strain Detected In SF
- Mpox cases are rising across California, and health officials say a rare strain was detected in San Francisco for the first time. - The discovery has prompted heightened surveillance, contact tracing, and concern among public-health teams. - Officials are urging eligible Californians to get vaccinated and take precautions to slow the spread (patch.com).
Mpox is a viral disease that usually spreads through close skin-to-skin contact, and San Francisco has now confirmed its first clade I case in a city resident. (sf.gov) San Francisco Department of Public Health said the case was confirmed on April 14, 2026, in an unvaccinated adult who was hospitalized and is improving. The patient reported close contact with someone who had traveled internationally to an area where clade I mpox is circulating. (sf.gov) Clade is the virus’s family branch, like one limb on a tree, and clade I is different from the clade II strain that has circulated in California since 2022. California health officials said this San Francisco case is the state’s seventh identified clade I case since November 2024 and its first in San Francisco. (cdc.gov; cdph.ca.gov) State officials said they have started enhanced surveillance and contact tracing around the San Francisco case. San Francisco also sent a health alert to clinicians on April 16 telling them to watch for suspected cases and report them quickly. (cdph.ca.gov; sf.gov) California is also dealing with the older clade II outbreak at the same time. The California Department of Public Health said clade II cases rose in July and August 2025, especially in the San Francisco Bay Area, and the Centers for Disease Control and Prevention says most U.S. mpox cases are still clade II. (cdph.ca.gov; cdc.gov) The Centers for Disease Control and Prevention said the risk from clade I to most people in the United States remains low. But the agency also said the United States reported 11 clade I cases from November 2024 through February 2026, plus five more reported since March 2026 that were not linked to each other. (cdc.gov) California already saw a change in October 2025, when state officials reported the first clade I cases in California and the United States without international travel. The state said those infections showed person-to-person community spread, primarily affecting gay and bisexual men, other men who have sex with men, and their social networks. (cdph.ca.gov) San Francisco health officials said the mpox vaccine protects against both clade I and clade II and urged people at higher risk to get both doses. State officials tied that push to summer travel and large events, saying April is the time to get protected before exposure happens. (sf.gov; cdph.ca.gov) San Francisco’s public dashboard says local case counts are updated Monday through Friday and can change as reports are confirmed. For now, the city’s first clade I case has turned a travel-linked infection into a local public-health response. (sf.gov; sf.gov)
