Health Alert: San Franciso Reports First Clade I Mpox Case

Disease Prevention and Control

Situational Update

On April 14, 2026, the first clade I mpox case in San Francisco (SF) was confirmed. The case occurred in an unvaccinated adult who was hospitalized and is improving. The individual reported close contact with someone who traveled internationally to an area where clade I mpox is circulating.

Clade I mpox is distinct from clade II mpox. The mpox outbreak in the United States that began in 2022 is due to clade II mpox and has led to 1066 cases in SF as of April 9, 2026. In contrast, an outbreak of clade I mpox in Central and Eastern Africa has been ongoing since 2023, with sporadic travel-associated cases reported in non-endemic countries and increasing reports of locally-acquired clade I mpox in Europe. Over the last two years, 15 clade I mpox cases have been reported in the United States, including 6 in California. Public health officials are monitoring cases to determine if clade I mpox is more severe than clade II mpox in the United States.

In San Francisco, clade II mpox cases have typically remained low in the winter and early spring, with <10 cases in the first quarter of prior years. In contrast, in 2026, 24 SF residents were diagnosed with clade II mpox from January-March 2026. Cases of clade II mpox may increase further in the summer and fall with events and travel that have previously been associated with increased cases.

Recommendations for SF Clinicians

Prevention

  1. Recommend JYNNEOS vaccination for patients at risk of mpox exposure.
    1. Include assessment of mpox risk and vaccination status at all visits for men, trans, or nonbinary people who have sex with men, trans, or nonbinary people.
    2. Persons planning travel to an area where clade I mpox is circulating should receive mpox vaccination if they anticipate having sex with a new partner, sex at a sex club or bathhouse, sex in exchange for money or other trade, or sex in association with any large public event such as a festival.
    3. The two doses are administered 28 days apart. If a person received 1 dose >28 days ago, the second dose can be administered immediately.
    4. The vaccine is safe for people who are immunocompromised or taking immune suppressing medications.
    5. Vaccination is not recommended in persons who have previously been diagnosed with mpox as infection confers immune protection.
    6. Booster doses are not recommended.
  2. Counsel patients that vaccination with JYNNEOS significantly reduces the risk of mpox infection and severe disease but is not 100% effective at preventing all disease. Condom use and reducing the number of sex partners are additional strategies to reduce risk.

Diagnosis, Testing, and Infection Control

  1. Recognize that both clade I mpox and clade II mpox may present with flu-like symptoms, including fevers, chills, lymphadenopathy or malaise, for several days before or simultaneously with development of mpox lesions.
  2. Have a heightened index of suspicion for clade I mpox in patients of any age or gender who present with signs and symptoms consistent with mpox AND who report either:
    1. recent international travel to an area where clade I is circulating, OR
    2. sexual contact with someone who recently traveled internationally to an area where clade I is circulating.
  3. Recognize and test suspected lesions. Follow specimen collection guidelines and your laboratory’s submission criteria to submit 2 swabs, 1 each from separate lesions.
  4. Follow infection prevention and control recommendations for all patients with mpox symptoms.

Treatment

  1. Provide supportive care and symptomatic treatment to patients diagnosed with clade I or clade II mpox.
    1. There is no FDA-approved treatment for clade I or clade II mpox infection.
    2. TPOXX monotherapy was not found to be effective for patients with mild to moderate mpox.
  2. Consider use of TPOXX in combination with Brincidofovir for patients with severe immunocompromise or patients at risk of severe disease.
    1. To request TPOXX and Brincidofovir for a patient who meets CDC eligibility criteria, contact SFDPH at the phone numbers provided below.

Reporting

  1. Notify SFDPH immediately if clade I mpox is suspected. To report a suspected clade I mpox case, call 628-217-6688 Monday-Friday 8 am to 5 pm. For after hours, weekend, and holiday reporting, call 628-217-6100 and follow instructions to page the on-call clinician.
  2. Report clade II mpox cases by submitting a Confidential Morbidity Report form by email (DPH-STIReactorDesk@sfdph.org) or fax: (628) 217-6603.

References:

More information about mpox can be found here:

To view or sign up for SFDPH Health Alerts, Advisories, and Updates visit: sf.gov/healthalerts