Using sewage epidemiology to monitor SARS-CoV-2 in Houston

With cases of coronavirus disease (COVID-19) skyrocketing around the world, understanding the full extent of the pandemic is of paramount importance. However, it is an ongoing challenge for public health officials.

Currently, diagnostic testing capacity may be insufficient, and in some hospitals, reporting of COVID-19 patients is delayed for weeks. Furthermore, many infected individuals do not develop symptoms, making it more difficult to identify who should be isolated and quarantined.

In past viral disease outbreaks, scientists monitor sewage or wastewater for traces of a pathogen for effective population surveillance.

Now, a team of researchers from Rice University, Baylor College of Medicine and the Houston Department of Health shows that SARS-CoV-2 RNA wastewater levels are a strong predictor of nasal positivity rate trends with two weeks in advance. This could help monitor the positivity rate for populations, accelerating the isolation and treatment of infected people.

Wastewater monitoring in Houston shows that SARS-536 CoV-2 levels monitor the rate of positivity. (A) Overview of the SARS-CoV-2 Weekly Wastewater Surveillance System. (B) A non-linear (spline) regression was suitable for the observations of each WWTP (the + symbols connected by lines represent the same WWTP; the size of the + indicates the level of uncertainty). The individual splines were transformed into inverse log10, added together and then 1og10 transformed to form the overall spline (green line). The gray line is the 95% confidence band for the overall estimate derived from the sum of variances (each spline). (C) The green line is the average spline for the viral wastewater levels for the 16 WWTPs (from panel B). The dark blue line is the 14-day moving average of the positivity rate (+ denoting the daily observations; the blue line shows the non-linear regression (spline) suitable for those observations). Gray represents the 95% confidence bands. (D) Log10 total positive clinical cases versus log10 total viral load during the study period. The symbols indicate the positive cases of WWTP and the total viral load. Green symbols indicate viral charges and cases of wastewater (11 May – 5 October) and sites with red symbols between 8 July and 5 October.

I study

Wastewater surveillance or monitoring for SARS-CoV-2 provides a way for real-time monitoring of infection in the community. Although COVID-19 is considered a respiratory disease, viral RNA can be detected in wastewater because infected people also excrete SARS-CoV-2 in the stool.

Around the world, SARS-CoV-2 RNA has been detected in many wastewater samples. Wastewater monitoring for SARS-CoV2 has many benefits, including cost-effectiveness, as a complementary tool to diagnostic testing and could identify outbreaks prior to diagnostic testing. In addition, wastewater surveillance avoids bias of other epidemiological indicators and collects information from people who do not have access to primary health care.

If surveillance successfully reveals the dynamics of infection before diagnostic testing, government and public health officials will have near real-time data on disease prevalence.

To arrive at the study results, published on the pre-press server medRxiv *, Researchers conducted a comprehensive sewage monitoring program for coronavirus in Houston, Texas, a city of 3.6 million people. The city experienced a spate of cases, hospitalizations and deaths between May and October.

The team collected samples from 39 of the city’s wastewater treatment plants. They detected SARS-CoV-2 RNA levels in wastewater providing a two-week warning for changes in the positivity rate.

From May to October, the team collected and analyzed 24-hour time-weighted composite influential samples from 16 to 39 wastewater treatment plants once a week. The team collected these samples on the same day every week.

Results of the study

The study results showed that wastewater levels of SARS-CoV-2 RNA were the strongest predictor of trends in the positivity rate about two weeks ahead.

“Given the strong predictive relationship of wastewater viral load and positivity rates, wastewater monitoring represents a viable approach to test the entire Houston population simultaneously and a means to provide continuous, weekly monitoring of the entire population. “concluded the researchers in the study.

Additionally, viral RNA loads from wastewater showed robust and powerful monitoring of the positivity rate for those served by individual treatment plants. These results could be used in real time to establish public health interventions.

The team noted that wastewater monitoring is a quick and cost-effective approach to achieving comprehensive coverage of large populations. However, the researchers also believe that further research is important for estimating the prevalence of wastewater disease.

The team also recommends that the method be used not only in cities but also in the national and global community. In this way, those areas where diagnostic tests are expensive and impossible may have the means to test for the spread of COVID-19.

“After a vaccine has been developed and administered, wastewater monitoring can facilitate early detection of SARS-CoV-2 reappearance in communities and be used to direct resources for vaccine delivery, in line with previous work. carried out in the 1960s which facilitated the acceleration of delivery of the oral polio vaccine to prevent outbreaks, “the researchers added.

The United States remains the nation with the highest number of cases, reaching over 10 million cases. The death toll in the country exceeded 238,000. Globally, the number of cases has surpassed 50.8 million and the number is expected to increase in the coming weeks as more and more countries are experiencing the second wave of the virus.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as consolidated information.