State of California—Health and Human Services Agency
California Department of Public Health

Health Advisory

TO: Healthcare Providers

First Clade I Mpox Case Confirmed in California and the United States in a Returning Traveler

11/19/2024

Key Messages

On November 15, 2024, testing at the California Department of Public Health (CDPH) confirmed the first case of mpox infection from clade I monkeypox virus (MPXV) in the United States. The patient recently traveled from an affected country, where clade I MPXV is actively spreading. The patient has relatively mild illness and is recovering after seeking medical care for mpox symptoms.

CDPH along with local health departments (LHD) and the U.S. Centers for Disease Control and Prevention (CDC) are investigating potential contacts to the patient; no additional cases have been detected to date. The overall risk of clade I mpox to the general population in California and the United States continues to be low.

CDPH and the CDC have been preparing for prompt detection and response to potential clade I cases as clade I MPXV has historically been more transmissible and caused more severe disease than clade II MPXV. However, recent outbreaks have reported death rates as low as 1% when patients received good medical oversight and supportive clinical care.

Health care providers are advised to follow infection prevention and control recommendations for all patients with mpox symptoms and have a heightened index of suspicion for clade I mpox in patients who present with signs and symptoms consistent with mpox and who report either: (1) recent international travel, or (2) sexual or close contact with someone who recently traveled internationally, particularly to Central or East Africa.

Follow specimen collection guidelines. Use full PPE and 2 sterile synthetic swabs to vigorously swab and collect specimens from ~2-3 lesions. Do not de-roof or aspirate lesion(s) due to risk of sharps injury and exposure.

If clade I mpox infection is suspected, patients should be advised to isolate and providers should notify their local health department immediately and work with them to send specimens for expedited clade-specific mpox testing, which is available at the CDPH Viral and Rickettsial Disease Laboratory (VRDL).

For specimen submission criteria and shipping instructions to CDPH VRDL, see CDPH VRDL MPXV PCR Test Order. Contact information for the CDPH VRDL: (510) 307-8585 or VRDL.Submittal@cdph.ca.gov.

Medical countermeasures used in the ongoing clade IIb global outbreak, including the mpox vaccine, are anticipated to be effective for clade I MPXV.
In August 2024, initial results from a study in the Democratic Republic of the Congo showed that tecovirimat (TPOXX) was safe but did not improve clade I mpox resolution. Additional data analyses are underway to better understand the results of this study, including if there was any benefit to a subset of people who received TPOXX. Providers should contact their local health department to access medication for any patients who have severe manifestations or are immunocompromised. Inform patients with mpox about the STOMP trial (STOMP Trial, call 1-855-876-9997) and recommend that they enroll. Oral TPOXX is available through the STOMP trial.

Providers and LHDs should continue to encourage vaccination for patients who may be at risk for mpox. Vaccination is particularly important for people with weakened immune systems related to HIV infection or other conditions as they are at risk for severe disease. Vaccination coverage in California remains low, with less than half of people who are eligible to receive the vaccine having received both doses of JYNNEOS vaccine.

The Advisory Committee on Immunization Practices (ACIP) recommends vaccination for people ≥18 years of age who may be at risk for mpox, which now includes people who are traveling to countries with ongoing person-to-person transmission of clade I mpox who anticipate sexual activities, with two doses of the JYNNEOS vaccine (at least 28 days apart).

JYNNEOS may also be given as post-exposure prophylaxis to asymptomatic persons ideally within 4 days but up to 14 days after exposure if they have not already received two doses of vaccine or been previously infected with mpox.

For more information on the evolving clade I mpox situation and recommendations for LHDs, providers, laboratories, and the public, please see the CDC Health Advisory: First Case of Clade I Mpox Diagnosed in the United States.

CDPH STD Control Branch: stdcb@cdph.ca.gov or mpoxadmin@cdph.ca.gov; phone: (510) 620-3400.

CDC Poxvirus and Rabies Branch: poxvirus@cdc.gov or for emergencies, CDC's 24/7 Emergency Operations Center (EOC): 770-488-7100. General inquiries: CDC-INFO (1-800-232-4636).

LHD Communicable Disease Contact Information: California Conference of Local Health Officers (CCLHO). If unable to reach the LHD, healthcare providers may contact the CDPH Duty Officer at (916) 328-3605.