Health Advisory: Be Alert for Mpox: Clade I Mpox Virus Detected in Wastewater; Rise in Cases of Clade II Mpox

09/29/2025

This is a Provider Alert from the Washington State Department of Health (WA DOH) Office of Infectious Disease. WA DOH is requesting that providers remain alert for cases of mpox due to:

A recent detection of clade I mpox virus in wastewater in Pierce County, and
Rising cases of clade II mpox.

Current Situation:

Mpox (formerly “monkeypox”), the infection caused by the mpox virus (MPXV), has been circulating at low levels in Washington State since the 2022 global outbreak of clade II mpox. We have recently seen an increase in clade II mpox cases in the Puget Sound Area, associated with sexual and intimate contact among gay, bisexual, and other men who have sex with men, transgender people, and non-binary people.

In addition, WA DOH has been monitoring for potentially more severe strain of mpox (clade I) since 2024 due to an ongoing outbreak of clade I mpox in Central and East Africa. To date, we have not identified any cases of clade I mpox in Washington, although other states have identified travel-related clade I mpox cases.

On September 24th, 2025, WA DOH and Tacoma-Pierce County Health Department (TPCHD), in collaboration with the University of Washington, were notified that a wastewater monitoring site in Pierce County detected clade I MPXV. WA DOH has not yet been notified of a case of clade I mpox, and the risk to the community remains low.

Due to the increase in cases of clade II mpox, and the increased likelihood of detecting a case of clade I mpox in Washington after the wastewater detection, WA DOH would like to remind local health jurisdictions and healthcare providers of the following:

Be alert for patients with compatible signs and symptoms of mpox.
Use travel history to assess the risk of clade I mpox – i.e., patients with recent travel to (or close contact with people who have traveled to) Central or East Africa.
Vaccinate at-risk individuals, and vaccinate exposed persons as post-exposure prophylaxis (PEP).
Be aware that mpox continues to primarily, but not exclusively, affect gay, bisexual, or other men who have sex with men (MSM), transgender people, and nonbinary people.

Actions Requested:

Immediately report all suspected cases of mpox to your Local Health Jurisdiction (LHJ).
Consider mpox on your differential for any patients with signs and symptoms of mpox, even if:
- Diagnosis of syphilis or herpes is considered more likely (co-infections can occur)
- The patient has a history of mpox vaccination. Mpox infections in people who previously received one or more vaccine doses are usually:
  - Less severe
  - May present subtly as proctitis without anogenital lesions, or with only a few lesions
  - May present without prodromal constitutional symptoms.
Be aware of the ongoing outbreak of clade I mpox circulating in Central and East Africa.
Be aware that there is noclinical distinction in the signs and symptoms of clade I mpox and clade II mpox.
- Suspect clade I mpox infection in a patient with compatible signs of mpox AND:
  - Reported recent travel to Central or East Africa (or other areas with ongoing clade I mpox transmission), AND/OR
  - Contact with a confirmed or suspected clade I mpox case.
Testing for mpox:
- Testing may be available through your facility’s clinical or commercial laboratory.
- If possible, choose a PCR test option that includes clade determination testing.
- Follow mpox specimen collection guidelines for your facility, or refer to specimen collection guidelines from WA DOH.
If you do not have access to clade determination testing and suspect clade I mpox, contact your Local Health Jurisdiction to request testing at the WA Public Health Laboratories (PHL).
- Do NOT send specimens to the PHL without prior approval from your Local Health Jurisdiction.
The treatment and management for patients with clade I mpox is the same for clade II mpox.
- Most immunocompetent patients with mpox will improve with supportive care alone.
- Mpox treatment is available under the CDC’s Investigational New Drug Protocol for qualifying patients who are immunosuppressed or have severe disease.
- Contact your Local Health Jurisdiction and/or WA DOH at mpoxconsult@doh.wa.gov for assistance with evaluating need for therapeutics.
Continue to vaccinate individuals who are eligible to receive mpox vaccination.
- Mpox vaccine is effective against both mpox clades.
- Booster doses are currently not recommended by the CDC if someone has already completed their series.
- Obtain vaccine from commercial suppliers.
  - WA DOH offers limited doses of JYNNEOS vaccine to clinics who serve individuals for whom vaccine is recommended (see Mpox Vaccine Opportunity).
Offer the mpox vaccine as post-exposure prophylaxis (PEP) to individuals who have had direct contact with someone with mpox. PEP is effective against both mpox clades.
- Encourage patients to work with local health jurisdictions to connect close contacts and sexual partners to PEP.
- PEP should be offered as soon as possible after exposure to someone with mpox:
  - Within 4 days of exposure to prevent illness
  - Up to 14 days after exposure to reduce risk of severe disease.
Offer HIV and syphilis testing, mpox vaccination, HIV pre-exposure prophylaxis (PrEP), and doxy-PEP to patients who are gay or bisexual men, or the sex partners of gay or bisexual men.
Travel health providers should conduct a sexual health history with patients and offer mpox vaccination to travelers visiting a country with sustained clade I mpox transmission regardless of the patient’s gender identity or sexual orientation, if they anticipate experiencing any of the following:
- Sex with a new partner,
- Sex at a commercial sex venue, like a sex club or bathhouse,
- Sex in exchange for money, goods, drugs, or other trade,
- Sex in association with a large public event or festival.

Background

MPXV is the virus that causes mpox infection. Since the 2022 global outbreak of mpox, mpox has continued to occur in WA with a pattern of diagnoses concentrated in the late summer and fall. Mpox is often associated with a painful rash, frequently located on the genitals or anus, along with other symptoms, that progresses through several stages. Mpox is spread through close contact with a person with mpox, direct contact with contaminated materials, or direct contact with infected animals.

There are two clades of MPXV, clade I and clade II. While both clades cause similar symptoms, there is historical evidence that clade I MPXV is more transmissible, and often causes more severe disease than clade II, with case fatality rates reported up to 10%, with higher risk for children and pregnant people. However, people with clade I mpox who are provided high-quality supportive care have a significantly lower mortality than those who were not connected to care. The management of clade I mpox is similar to that for clade II mpox. Mpox continues to be reported across the United States and six clade I cases have been reported in the United States.

Tecovirimat, or TPOXX, is an antiviral for smallpox that was used for mpox treatment during the 2022 global clade II outbreak. Initial results from two clinical trials have demonstrated that tecovirimat is safe to use for people with mpox, but that it did not reduce the time to resolution of mpox lesions. Tecovirimat efficacy is still being evaluated for patients who are immunocompromised and for those with severe disease. Tecovirimat, along with other investigational drugs, are still available under CDC’s expanded access Investigational New Drug Protocol for eligible patients.

Resources

Contact:

To report suspected cases, for questions about staging a syphilis case, or for any other questions, please contact:

Yakima Health District

(509) 249-6541