Measles Virus in Wastewater a Concern For Public Health

Authored By:

Venkat Rao

There have been numerous reports in the past few years on the detection of SARS-CoV-2 in wastewater as a reliable indicator of the prevalence of COVID-19 disease in the communities in the drainage network.

Interestingly, Texas, Austin Public Health reported in July detection of Measles virus in wastewater samples collected from the Travis County drainage network with urging all residents to update the status for measles, mumps, and rubella (MMR) vaccination. Although Travis County in Texas has reported only two confirmed cases of measles, wastewater surveillance results may point to a wider prevalence of the virus in the environment and undetected cases.

Measles is regarded as the most contagious infectious disease in the world. A single measles-infected person can spread the virus to as many as 18 others in a susceptible population. Measles spread through person-to-person droplets in the breadth that are released into the air during coughing, sneezing, and speaking. The virus remains viable (alive) for nearly 2 hours suspended in the air. Given that the virus is highly contagious, large-scale vaccination and herd immunity are keys to stopping the spread of the virus.

In the past few months, other states have reported detection of measles virus in wastewater samples from the Provo area in Utah, Luna county in New Mexico, sewer district area of Sacramento, California.

Wastewater surveillance for infectious diseases has been in practice has been around since the 1050s when Typhoid—a life-threatening infection caused by the bacterium Salmonella typhi, that spread through contaminated water and food—was detected in the wastewater samples serving as a source of disease transmission surveillance to track spread of the disease.

Essentially, wastewater surveillance involves collection of sewage water samples at various locations with a sewage network starting either from a node within the network collecting sewage from a smaller residential block or collecting samples downstream at centralized locations that receive sewage from nodes upstream. Obviously, downstream, centralized locations aggregate multiple nodal locations upstream and represent a much larger community, whereas upstream samples are from smaller clusters of homes enabling detection of infected individuals that much easier.

A good illustrative example of this approach is the University of Arizona study which utilized sampling of sewage samples from student housing blocks and detected in near real-time appearance of SARS-CoV-2 virus in the sewage to specific housing bloc and three SARS-CoV-2 infected students, one symptomatic and two asymptomatic, as they re-entered the campus to attend the fall semester. Positive detection of virus RNA was used to target re-entry dates of students to identify virus-infected students. This study serves as a good example of using wastewater-based epidemiology to monitor infectious diseases.

During the early phase of the COVID-19 pandemic, in 2020, scientists employed wastewater samples from Madrid region to pinpoint temporal appearance of SARS-CoV-2 virus with prior patients visit to hospital with COVID-19 symptoms, which is now a proven a monitoring technique used by public health department all over the United States and elsewhere.

The recent study implied undetected cases of measles in the Travis County, TX. This follows an earlier report from the Utah Department of Health and Human Services that measles virus was detected in wastewater samples collected from the Provo area, suggesting at least one person was infected with the virus. As of this week, 36 cases of measles are reported in Utah compared to only 22 cases early in the month, which is a significant increase in the number of cases reported in Utah. Other states tracking wastewater for measles include New Mexico and California in the Sacramento area where confirmed cases of measles are reported based on surveillance of wastewater.

Nationwide data is now available for tracking and detecting measles based on wastewater surveillance.

A network of public health scientists has established the WastewaterSCAN providing information consolidated information on wastewater tracking for more than a dozen infectious diseases across the country and share the surveillance data for use by public health agencies. Data collected from nearly 150 wastewater treatment facilities across 40 states provide highly valuable surveillance and early detection of highly infectious diseases such as measles, so preventive measures could be implemented by the public health agencies before the infection takes a foot hold in the community. Early in the summer, WastewaterSCAN surveillance data allowed the detection of  measles virus RNA at three locations Hollywood (MD), Sacramento (CA), and Stamford (CT).CDC’s National Wastewater Surveillance System (NWSS) monitors wastewater at 1400 locations across the nation and does not yet include measles virus. As of now NWSS monitors COVID-19, Influenza A, Avian Influenza A (H5), Respiratory Syncytial Virus (RSV), and Monkeypox (Mpox).

Note that public health agencies have been monitoring wastewater for infectious disease for nearly a century starting with polio in the 1930s. Wastewater surveillance not only provided the presence of a viral pathogen in the community, but its presence was also linked to the projected number of cases in the affected community. As a result, public health agencies have employed wastewater surveillance where applicable to detect, contain and eradicate infectious disease outbreak.

Prior results from polio virus monitoring in wastewater network provided the basis for one of the largest sewage waters surveillances for COVID-19 in global public health history. As described earlier, wastewater surveillance provided a reasonably good estimate on the number of symptomatic and non-symptomatic cases of COVID-19 in the community linked to the wastewater network. However, surveillance of infectious disease through other data sources such as environmental monitoring such as air, food and wastewater and prescription drug buying trends at local pharmacies has not gained the prominence that they deserve. Wastewater surveillance technique provides exceedingly early data for the presence of a viral pathogen in the community and help identify cases well before patients show up at hospitals with symptoms of the disease, creating increased risk of person-to-person contact and transmission of the disease, as it happened with the COVID-19 pandemic.

Sewage water monitoring involves collection of samples at various nodal locations in the sewage network. Samples collected at upper end of the network connected to the apartment or building levels enable precise estimation of the number of cases, compared to the lower aggregated ends closer to the sewage treatment areas. Surveillance plan generally adopt sampling at localized level. Pathogens such as SARS-CoV-2 and measles virus are predominantly excreted via fecal matter and remain relatively stable in wastewater, making them excellent candidate for wastewater monitoring for community level surveillance for the suspect disease.

Although wastewater surveillance caught public attention during the COVID-19 pandemic, it is nothing new  to researchers and public health agencies. As a surveillance tool, wastewater monitoring for measles is a useful public health tool as it provides geospatial information on the size and scope of prevalence of a pathogen in the community. Measles patients shed the virus in urine, feces, and saliva, making it an ideal candidate for wastewater surveillance.