The Hawaii Department of Health announced April 27, 2026 that a wastewater sample collected on April 13 from a treatment facility at Joint Base Pearl Harbor-Hickam on Oahu tested positive for clade I mpox.
The sample came from a facility that serves on-base military housing and public sites including the Pearl Harbor National Memorial Museum. The department received notice of the initial detection on April 20 and later received confirmatory positive results on April 24. A follow-up sample collected on April 20 from the same facility tested negative.
Health officials emphasized that this is the first time clade I mpox has been detected in wastewater in Hawaii, and stressed that no clinical case of clade I mpox has been identified in the state. "The presence of clade I mpox virus in wastewater does not confirm a clinical case or community spread," officials said, adding that the finding should be treated as a signal, not proof of infection among the population served by the facility.
The detection matters because it triggers heightened surveillance and public health guidance tied to a virus with distinct public-health implications. Major civilian wastewater facilities on Oahu are routinely tested for clade I mpox, and as of Wednesday all major civilian wastewater samples on Oahu had tested negative. The isolated positive at the Joint Base facility breaks that otherwise clean run of results and prompted the department to remind residents how mpox transmits and whom to watch for symptoms.
Officials reiterated known transmission pathways to put the result in practical terms: both clade I and clade II mpox spread through close contact with body fluids, lesion material or items used by someone with mpox. Mpox does not spread through the air or casual contact typically encountered in shared spaces like a classroom, office or swimming pool, the department said. Symptoms to monitor include a rash, fever, chills and swollen lymph nodes; the rash typically begins as bumps that progress to blisters and pustules on the hands, feet, chest, face or mouth, or near the genitals.
The discovery also revived a travel-linked pattern seen with clade I in the continental United States. So far, clade I cases in the continental U.S. have been among people who recently traveled to countries with ongoing outbreaks in Western Europe and Central and Eastern Africa. The department encouraged anyone who recently traveled to an area with active transmission, or who has been in close contact with a symptomatic individual, to monitor their health and consult a health care provider about testing and vaccination.
Health officials offered specific prevention advice for people at higher risk. "Instead, it serves as an indicator to be alert for possible mpox cases. People at higher risk of mpox infection should consider being vaccinated with two doses of the JYNNEOS (mpox) vaccine if not already protected," they said. The department reiterated that the risk to the general public remains low.
The tension in the report is plain: a positive environmental signal at a facility that serves both military housing and tourist sites, but no confirmed human illness connected to that signal. Wastewater detection can indicate viral shedding by an infected individual, transient contamination or even a false positive; health officials were careful to say the result does not establish community spread. The mixed set of results—an April 13 positive, notification April 20, a negative April 20 follow-up sample, and a confirmatory result April 24—left public-health authorities with a narrow, time-bound signal rather than a clear chain of transmission.
What happens next is already laid out by the department: continued wastewater monitoring, clinical surveillance and advice for people who may be at higher risk. Anyone who develops symptoms and believes they are at heightened risk should contact their health care provider immediately to discuss testing and vaccination. For the rest of Oahu, the department's public assessment is straightforward—low immediate risk, continued vigilance and more samples to read before any broader conclusion can be drawn.
