The California Department of Public Health has confirmed the first known case of clade I monkeypox (mpox) in the United States. This case is linked to a current outbreak of clade I mpox in Central and Eastern Africa. Despite the confirmation, the risk to the American public is considered low, with continuing sporadic cases of clade II mpox in the country.
The clade I mpox case was detected in an individual who recently traveled from Eastern Africa. The patient received treatment shortly after returning to the United States and has since recovered at home without further treatment specific to mpox. Symptoms are reportedly improving. Specimens from the patient have been verified as clade I mpox and are being forwarded to the Centers for Disease Control and Prevention (CDC) for additional viral characterization.
The CDC is collaborating with California health officials to trace and contact potential exposures. Casual contact, such as that experienced during travel, is deemed unlikely to significantly increase transmission risk. Current CDC guidelines suggest avoiding close contact with symptomatic individuals, steering clear of contaminated materials, and receiving the recommended mpox vaccinations if eligible.
There are two primary types of mpox, clade I and clade II, each with distinct subclades. The recently diagnosed case in California is particularly significant as clade I mpox had not previously been identified in the United States. Other travel-associated clade I cases have appeared in nations such as Germany, India, and the UK, with no related deaths reported.
Historically, clade I mpox has resulted in greater severity and higher mortality rates than clade II. However, recent data suggest infections from the ongoing outbreak are less severe. Past mortality rates for clade I ranged between 3%-11%, but recent outbreaks show rates below 1% with adequate medical support. This rate is even lower in countries like the U.S. with better healthcare systems.
Symptoms of mpox typically include a rash that can appear on various parts of the body, with an incubation period ranging from 3-17 days. This case of clade I mpox is part of a larger effort by the CDC to contain the virus’s spread, building on its experience with the clade II outbreak since 2022.
Preventive measures in the United States include wastewater monitoring to detect mpox presence, allowing for preemptive public health responses. The CDC extends its work internationally to mitigate transmission in Central and Eastern Africa through training, testing, and on-ground support.
Travelers to regions experiencing outbreaks are advised to stay informed and vigilant. More information is available online through the CDC’s dedicated mpox resource page.
