Healthcare Providers

On November 16, 2024, CDC and the California Department of Public Health announced the first clade I mpox case in the U.S.

• The patient had recently traveled from Eastern Africa, where there is an ongoing clade I mpox outbreak.
• On November 18, CDC issued a Health Alert Network Health Advisory .

About Clade I

Clade I mpox has historically caused more severe illness and deaths than clade II mpox, which is the cause of the 2022 global outbreak. However, recent data indicate that infections from clade I mpox in the current outbreak may not be as clinically severe as in previous outbreaks.

CDC recently assessed the risk to the U.S. posed by the clade I mpox outbreak. Currently:

• The risk to the U.S. overall population remains low.
• The risk to men who have sex with men (MSM) and people who have sex with MSM, regardless of gender (via sexual transmission) is low to moderate.

Recommendations for Clinicians

• Consider mpox as a possible diagnosis in patients with epidemiologic characteristics and lesions or other clinical signs and symptoms consistent with mpox. Ask about travel history.
• Test all suspected cases for mpox, even if the person has been vaccinated or had mpox in the past.
• Contact your local health department if a patient with suspected mpox has traveled or had contact with someone with mpox symptoms who traveled to Central or Eastern Africa the 21 days before symptom onset so that clade-specific testing can be performed through the state lab, the Division of Consolidated Laboratory Services (DCLS).
• Discuss mpox prevention and risk reduction strategies with all travelers to countries with ongoing human-to-human transmission of clade I mpox.
• Recommend vaccination to people who are eligible for mpox vaccine, including those who may have recent mpox exposure. Vaccines are expected to be effective for both clade I and clade II infections.
• For more information, please see CDC’s HAN Advisory.

Additional Information on the Clade I Mpox Preparedness and Response

• CDC HAN Alert Advisory: First Case of Clade I Mpox Diagnosed in the United States (11/18/24)
• CDC Public Health Strategies for Mpox
• CDC HAN Alert Update: Prevention Strategies for Mpox, including Vaccinating People at Risk via Sexual Exposure, for U.S. Travelers Visiting Countries with Clade I Mpox Outbreaks (9/23/24)
• CDC HAN Alert Update: Mpox Caused by Human-to-Human Transmission of Monkeypox Virus in the Democratic Republic of the Congo with Spread to Neighboring Countries (8/7/24)
• CDC COCA Call: Mpox Update: Clinical Management and Outbreaks (6/27/24)
• CDC MMWR: U.S. Preparedness and Response to Increasing Clade I Mpox Cases in the Democratic Republic of the Congo — United States, 2024 (5/16/24)

Outbreak Updates

• Since January 2024, the Democratic Republic of the Congo (DRC) has reported more than 47,000 suspect clade I mpox cases and more than 1,000 deaths. The current outbreak is more widespread than any previous DRC outbreak and has spread to some neighboring countries. Clade I mpox historically has caused more severe illness or death compared to clade II but recent data suggest clade I mpox infections in the current outbreak may not be as severe as in previous outbreaks.
• On August 7, 2024, CDC reported that the DRC outbreak continues to grow and has resulted in clade I transmission to neighboring countries, including the Republic of Congo, Central African Republic, Burundi, Rwanda, and Uganda.
• On August 14, 2024, WHO determined that the upsurge of mpox in the DRC and a growing number of countries in Africa constitute a public health emergency of international concern (PHEIC).
• On August 15, 2024, the Public Health Agency of Sweden reported the first case of clade I MPXV infection outside of Africa. Since then, several additional countries outside of Africa have reported travel-associated clade I mpox cases.
• On November 16, 2024, CDC and the California Department of Public Health announced the first known clade I mpox case in the U.S.