Background 

Monkeypox virus (MPXV) has two distinct genetic clades, clade I and clade II. Each clade has sub-clades, including clade Ia, clade Ib, clade IIa, clade IIb. 

The 2022 global mpox outbreak was caused by clade IIb, which continues to circulate in the United States. Most clade IIb cases have occurred in gay, bisexual, transgender and other men who have sex with men (MSM). Clade II cases in San Francisco remain low, with 22 mpox cases reported in 2024 thus far. 

In contrast, an outbreak of clade I mpox has been growing in the Democratic Republic of the Congo (DRC) and neighboring countries since 2023. Thus far, no cases of clade I mpox have been detected in the United States. However, mpox clade I cases could be imported to the U.S. due to travel in areas where clade I is circulating. 

Mpox typically presents with skin lesions and may be preceded, accompanied by, or followed by fever, chills, lymphadenopathy or malaise. Constitutional symptoms may be absent. Symptoms typically appear within 3-17 days and can appear up to 21 days after exposure.

Situation Update 

Since late July 2024, clade I mpox has been reported in multiple non-endemic countries, including Rwanda, Uganda, Burundi, and Kenya. On August 7, 2024, CDC released a Health Advisory on clade I mpox, and on August 14, 2024, WHO declared the clade I mpox outbreak in central and east Africa a public health emergency of international concern. On August 15, the first clade I diagnosis outside of Africa was reported in Sweden. 

Since January 2023, there have been over 15,000 suspected or confirmed clade I cases in central Africa. There are uncertainties about the primary modes of clade I transmission, populations at risk, and severity. 

• Preliminary data show clade Ia is affecting mostly children, with multiple modes of transmission (e.g. close contact with infected persons or infected animals). 
• Clade Ib is affecting mostly adults, primarily through sexual contact. The case identified in Sweden is clade Ib.
• Historically, clade I has been associated with more severe illness compared with clade II. Approximately 3% of suspected mpox cases in the 2023 DRC clade I outbreak have been reported as deaths. There has been limited access to diagnostics, treatment, and prevention in the DRC. 
• The CDC anticipates medical countermeasures used for clade II to be effective for clade I, including the JYNNEOS vaccine, tecovirimat, brincidofovir, and vaccinia immune globulin. The STOMP trial, evaluating tecovirimat for mpox treatment in the United States, is ongoing and providers should continue to refer patients with mpox to the STOMP Trial. 

SFDPH is monitoring the outbreak alongside state and federal partners and will update guidance as the situation evolves.

Actions requested of SF Clinicians: 

We reiterate our previous recommendations for SF clinicians below, and are adding a new recommendation to suspect clade I mpox in patients with compatible symptoms who have recently returned from international travel, especially to the DRC, Central African Republic, the Republic of the Congo, Rwanda, Uganda, Burundi, and Kenya. These patients may include children and adults who are not MSM. 

1. Wear appropriate PPE when mpox is suspected.
2. Maintain awareness of potential mpox cases and recognize suspected lesions. Mpox may appear similar to other viral exanthems.
   • Screen patients with suspected lesions for recent travel or close contact, including sexual contact, with travelers returning from affected countries within the prior 21 days.
3. If infection with MPXV clade I is suspected based on both rash appearance and epidemiological risk factors, report the suspected case to SFDPH by phone at (628) 217-6639 from Monday to Friday, 8 am to 5 pm. For after hours and weekend reporting, call (415) 554-2830 and follow the instructions to page the on-call physician.
   • Please collect two specimens for testing. After calling SFDPH above to discuss, contact the SF Public Health Lab at 415-554-2800 to arrange for clade I testing from Monday to Friday, 8 am to 5 pm. Instructions for submitting specimens can be found at www.sf.gov/PHL
4. Recommend Jynneos vaccination among persons who are eligible. International travel alone is not currently an indication for vaccination. Two doses are administered 28 days apart. If a person has received 1 dose more than 28 days ago, the second dose can be administered immediately, and the series does not need to be re-started. Booster doses are not recommended at this time. Jynneos can be obtained commercially for administration in your office or clinic setting.
5. Counsel patients who are traveling to the DRC or surrounding countries to review the most up to date CDC Travel Health Notices and use precautions.
6. Refer anyone diagnosed with mpox to the STOMP Trial, a national randomized controlled trial on the efficacy and safety of tecovirimat (TPOXX). Persons with severe disease will be prescribed TPOXX and persons with mild to moderate disease will be randomized to either TPOXX or placebo. TPOXX can be prescribed by clinicians though an EA-IND protocol through the CDC. If you are not a TPOXX prescriber and would like to become one, information can be found here.

Additional Resources

SF.gov Mpox pages for the public: sf.gov/mpox

SF City Clinic Provider Pages: www.sfcityclinic.org/providers

CDPH Mpox: www.cdph.ca.gov/Programs/CID/DCDC/Pages/Mpox.aspx

CDC Health Alert: emergency.cdc.gov/han/2024/han00513.asp

Program Contact Information

San Francisco Department of Public Health

HIV/STI Prevention and Control Section

Tel: (628) 217-6074

Email: Julia.janssen@sfdph.org

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