Testing Wastewater: A Useful Tool for Tracking Moxp Outbreaks

In today's Morbidity and Mortality Weekly Report, researchers are sharing insights from two studies on mpox in the US. The studies delve into the effectiveness of wastewater detections and the implications of a 2023 outbreak in Los Angeles County.

The first study focuses on findings from the CDC's National Wastewater Surveillance System, which started testing US wastewater for mpox (formerly monkeypox) virus in October 2022, following a global outbreak mostly affecting men who have sex with men.

Covering samples collected from August 2022 through May 2023, the study aimed to determine the sensitivity and predictive values of wastewater mpox detection. Results showed that in a single week, a wastewater mpox detection had a sensitivity of 32% for one or more people shedding the virus, 49% for five or more people, and 77% for 15 or more people. The predictive values for cases per day and weekly were also outlined.

The authors emphasized that detecting Monkeypox virus in wastewater signaled the likely presence of at least one case in the county. Conversely, the absence of detection, combined with no reported cases, offered reassurance to public health officials.

The second study highlighted moderate levels of mpox transmission in LA County during spring and summer of the previous year, emphasizing the importance of vaccination. Although the county experienced high mpox levels in 2022, a decline was observed until an uptick in May 2023.

From May 4 to August 17, 2023, 56 mpox patients were identified, with only 29% fully vaccinated. One patient was hospitalized, and no deaths occurred. The outbreak mainly affected men, with 80% identifying as gay or bisexual. Among the cases, 57% were unvaccinated, 14% partially vaccinated, and 29% fully vaccinated.

The authors concluded that mpox was spreading at low levels within LAC, suggesting possible endemic transmission, especially with declining vaccination rates. They stressed the ongoing need for accessible mpox vaccination, particularly for those at risk of severe disease, including individuals with uncontrolled or advanced HIV, and groups with low vaccination coverage such as young, Black, and Hispanic individuals, and those living with HIV.