First US case of clade I mpox reported in California
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Key takeaways:
- The first U.S. case of clade I mpox is a California resident who returned home from travel in Eastern Africa.
- CDC and state health officials said there is no evidence the mpox strain is circulating in the U.S.
The first known U.S. case of an mpox clade that has historically been more transmissible and deadly was detected in California in a person who had recently returned from travel to Eastern Africa, according to health officials.
The California Department of Public Health confirmed the case of clade I mpox, which has been causing an outbreak centered in the Democratic Republic of the Congo (DRC), leading WHO to declare a global public health emergency in August.
“This case is related to an ongoing outbreak of clade I mpox in Central and Eastern Africa,” the CDC said in a press release. “The risk of clade I mpox to the public remains low, and there continue to be sporadic cases of clade II mpox in the United States.”
According to California health officials and the CDC, the person was treated in San Mateo County, California, after returning from Eastern Africa and was tested for mpox because of their travel history and symptoms.
Since testing positive for clade I mpox, the person has been isolating at home and their symptoms have been improving, the CDC said.
In 2022, clade II mpox caused a global outbreak that reached more than 111 countries, causing 92,000 infections worldwide. At its height in the U.S., the outbreak was linked to more than 2,000 new cases per week.
The CDC first issued a health alert about clade I mpox to U.S. physicians in December 2023. The clade was previously associated with non-sexual routes of transmission, but has been spreading through sexual contact in this outbreak, WHO has said. The clade also has historically been associated with more severe illness and higher case fatality rates than clade II, but recent data show that might not be true in this outbreak, the CDC noted.
“While outbreaks of clade I mpox used to have death rates around 3%-11%, more recent outbreaks have had death rates as low as approximately 1% when patients received good medical oversight and supportive clinical care,” the CDC said. “Death rates are expected to be much lower in countries with stronger health care systems and treatment options, including the United States.”
In June, the CDC published the results of a modeling study that found “close-contact transmission within and between households is unlikely to result in a large number of mpox clade I cases in the United States.”
According to the California Department of Public Health, people who had close contact with the patient with clade I mpox are being contacted. The department said “there is no concern or evidence that clade I mpox is currently spreading between individuals in California or the United States.”
Mpox vaccination is approved in the U.S. for adults and available to at-risk adolescents in the under an emergency use authorization. It has been commercially available at pharmacies, physician offices and other facilities that normally vaccinate since earlier this year.
References:
- California confirms first clade I mpox case. https://www.cdc.gov/media/releases/s1116-california-first-clade.html. Published Nov. 16, 2024. Accessed Nov. 18, 2024.
- California reports first known U.S. case of emerging mpox strain. https://www.cdph.ca.gov/Programs/OPA/Pages/NR24-036.aspx. Published Nov. 16, 2024. Accessed Nov. 18, 2024.
- CDC Modeling household transmission of clade I mpox in the United States. https://www.cdc.gov/forecast-outbreak-analytics/about/modeling-forecasting/mpox-transmission.html. Published June 4, 2024. Accessed Nov. 18, 2024.
- CDC. Mpox in the United States and around the world: Current situation. https://www.cdc.gov/mpox/situation-summary/index.html. Updated Nov. 16, 2024. Accessed Nov. 18, 2024.
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