Genetic material from the more severe Clade 1 Mpox virus has been detected in United States wastewater for the first time without a link to a known travel-related case, officials in Pierce County, Washington, confirmed. The finding, identified in a sample taken on September 24, 2025, serves as a stark alert to public health authorities, suggesting potential undetected community circulation of a strain known to cause more serious illness than the Clade 2 variant that dominated the 2022 global outbreak.
The discovery was made by scientists at the Washington State Department of Health (DOH) and the University of Washington. While officials stress that the risk to the general public remains low and no human cases of Clade 1 mpox have been identified in the county, the development has triggered an immediate increase in local and national surveillance efforts. The Tacoma-Pierce County Health Department (TPCHD) is now working closely with the DOH and the U.S. Centers for Disease Control and Prevention (CDC) to expand wastewater testing and monitor the situation.
This detection is significant as it occurs against the backdrop of a large, ongoing Clade 1b mpox outbreak in Central and Eastern Africa, which the Africa CDC continues to classify as a Public Health Emergency of Continental Security. That outbreak has highlighted the virus’s potential for sustained human-to-human transmission and more severe outcomes.
Key Facts: Clade 1 Mpox in the US
- What Happened: Genetic fragments of Clade 1 mpox virus were detected in a wastewater sample from Pierce County, Washington.
- Date of Detection: The sample was collected on September 24, 2025, and confirmed in a public announcement on September 26, 2025.
- Significance: This is the first detection of Clade 1 in U.S. wastewater that is not linked to a confirmed, travel-associated human case. It suggests the possibility of undiagnosed infections in the community.
- Official Response: Local and state health departments, in consultation with the CDC, have increased the frequency and scope of wastewater testing in the region.
- Public Risk Level: Health officials state the immediate risk to the general community is low. There are currently no identified human cases of Clade 1 mpox in Pierce County.
- Global Context: A severe outbreak of a Clade 1b subvariant is ongoing in the Democratic Republic of the Congo and other African nations, with thousands of cases and hundreds of deaths reported in 2025.
Context: A Tale of Two Clades
Mpox, formerly known as monkeypox, is a viral illness caused by the monkeypox virus, a member of the same family as the smallpox virus. There are two primary genetic clades, or types, of the virus:
- Clade I: Historically found in Central Africa, this clade is associated with more severe disease, higher rates of hospitalization, and a case fatality ratio that has historically reached up to 10% in some outbreaks. The current outbreak in the Democratic Republic of the Congo (DRC) involves a subvariant known as Clade 1b.
- Clade II: This clade, historically found in West Africa, generally causes less severe illness. The 2022-2023 global mpox outbreak, which saw tens of thousands of cases in the United States, was caused by the Clade IIb subvariant.
The detection in Pierce County is notable precisely because it is Clade 1. While the U.S. has successfully managed the widespread Clade IIb outbreak with vaccines and treatments, the appearance of Clade 1, even in wastewater, requires a more cautious approach due to its higher intrinsic severity.
Latest Data and Statistics
- Pierce County Detection (Sept. 2025): The Washington State Department of Health and the University of Washington detected Clade I mpox virus DNA in a wastewater sample collected on September 24, 2025.
- U.S. Mpox Cases (2025): The United States continues to see a low but steady level of Clade II mpox transmission. As of early September 2025, the CDC’s national case trend data showed a consistent 7-day average of approximately 3-5 new cases per day nationwide. These are overwhelmingly the less severe Clade IIb strain. (Source: CDC, U.S. Case Trends: Clade II Mpox.
- African Clade I Outbreak (2025): The broader context for this vigilance is the African outbreak. According to a World Health Organization report, from January 1 to September 14, 2025, 25 countries in Africa have reported a total of 34,273 confirmed mpox cases, including 158 deaths. The Africa CDC’s Emergency Consultative Group recommended on September 2, 2025, that the Public Health Emergency of Continental Security remain in place due to the ongoing threat. (Source: WHO, Multi-country outbreak of mpox, External situation report
Official Responses and Expert Analysis
Local officials have been quick to respond while aiming to prevent public alarm.
This is a rare occurrence, and also a great example of how public health keeps a close eye on disease spread to assess risk and inform the community when needed,” said Dr. James Miller, Health Officer for Tacoma-Pierce County, in a statement. “The risk to the community from clade I mpox remains low. If you have symptoms of mpox, you should consult your healthcare provider.
The CDC’s National Wastewater Surveillance System (NWSS) is a critical, non-invasive tool that helps public health officials understand disease trends. By testing sewage, they can detect viruses being shed by people with and without symptoms. Public health experts widely agree that a wastewater detection, particularly for a less common pathogen, is a powerful early warning signal. It suggests that at least one person in the sewershed—the area served by the wastewater treatment plant—is infected and shedding the virus, whether they have sought medical care or not.
While no specific CDC official has commented directly on the Pierce County finding, the agency’s own research has validated the utility of this method. A CDC study on mpox wastewater surveillance from 2022-2023 found the technique was “sufficiently sensitive to detect even a single mpox case in these large, pooled samples,” serving as a vital complement to clinical case reporting.
Impact on People and What to Watch Next
For the residents of Pierce County and the broader U.S., the immediate guidance has not changed. Mpox spreads primarily through close, personal, often skin-to-skin contact with the infectious rash, scabs, or body fluids. It can also be spread by respiratory secretions during prolonged, face-to-face contact.
Symptoms to watch for include:
- Fever and chills
- Swollen lymph nodes
- Headache and muscle aches
- A rash that can look like pimples or blisters, which may be painful or itchy and appear on or near the genitals or anus, but could also be on other areas like the hands, feet, chest, or face.
Health officials are urging healthcare providers to be vigilant. They are encouraging doctors to consider mpox in any patient presenting with a characteristic rash and to inquire about recent travel history to assess the risk of Clade 1 infection.
The key developments to watch next will be:
- Expanded Wastewater Results: Further testing in Pierce County and surrounding areas will reveal if the detection was an isolated event or if the virus is present more broadly.
- Clinical Surveillance: A crucial question is whether this wastewater signal translates into any clinically diagnosed human cases of Clade 1 mpox.
- CDC Guidance Updates: The CDC will continue to monitor the situation and may issue updated guidance for clinicians and the public based on new data.
The detection of Clade 1 mpox DNA in Washington state wastewater is a testament to the power of modern public health surveillance. While it does not signal an impending outbreak, it serves as a critical and timely warning.
It underscores the interconnectedness of global health—where a public health emergency in Central Africa can have faint but important echoes in a community in the Pacific Northwest. For now, the message from health officials is one of vigilance, not panic, as they work to understand the full significance of this silent signal from the sewers.
The Information is Collected from Times Now and Times of India.
