Coronavirus wastewater data and CDC guidelines can provide conflicting signals about whether to mask


Detecting coronavirus levels in wastewater offers an alternative to monitoring community spread as many Americans try to move on from the pandemic's peak and as testing dwindles.

Coronavirus wastewater data and CDC guidelines can provide conflicting signals about whether to mask

The CDC collects wastewater data for approximately 650 sewersheds, which represent roughly a quarter of the US population. The amount of virus detected on the majority of those sites has decreased in the last two weeks.

However, for some, the virus load has increased by at least 1,000% compared to 15 days ago.

An early warning sign like this may prompt local leaders to refocus on prevention measures. However, with the vast majority of the country now living in areas with a low or medium "community level" of Covid-19, this surveillance data may contradict what the CDC recommends.

Most likely, the surveillance alerted officials to rising levels of infection days faster than more traditional measures such as testing numbers.

However, according to the new CDC guidelines, the majority of the locations where there has been a recent increase in the amount of virus detected in wastewater are in counties where indoor masking is no longer recommended.

Only four of the 28 sites with a 1,000 percent increase in the last 15 days are in counties with a "high" community level, where indoor masking is still universally recommended as of Wednesday. More than half are in counties with a "low" community level, where masking is not recommended at all.

Previously driven solely by local case rates, the CDC's new masking guidelines now heavily weigh hospital admissions and capacity. Some critics argue that they stray too far from Covid-19 prevention measures, such as minimizing coronavirus transmission.

The CDC continues to monitor community spread, and CDC Director Dr. Rochelle Walensky touted strategies that "can better anticipate a rise in cases" and alert people in real time, including wastewater surveillance, at a briefing last week.

According to the CDC, wastewater data is intended to supplement other surveillance tools. When wastewater levels are low, a small increase can appear to be a dramatic increase, according to Brian Katzowitz, a CDC health communication specialist.

However, it best informs public health decision-making when combined with other metrics.

Although wastewater data is not formally part of the CDC's new guidelines, Amy Kirby, programme lead for the National Wastewater Surveillance System, said the public health response to rising levels would be very similar to those taken if trends with other metrics headed in the wrong direction, including encouraged masking, social distancing, and vaccination.

The CDC has been collecting wastewater data from some sites for more than a year, but only recently has the data been made public.

Coronavirus wastewater data and CDC guidelines can provide conflicting signals about whether to mask

Since the national dashboard's launch, approximately 250 sites representing an additional 30 million people have been added, and new sites are still being added.

The federal dashboard displays coronavirus detection levels in sewersheds as a percentage change over the previous 15 days.

A watershed in St. Louis County, Missouri, serving approximately 116,000 people, was one of 28 on the CDC dashboard that recently saw a more than 1,000% increase in virus levels. However, data in this format, according to Dr. Mati Hlatshwayo Davis, director of the St. Louis City Department of Health, isn't always useful without an understanding of the baseline levels.

As at-home Covid-19 tests become more common – or as testing demand falls – wastewater provides a far more reliable and consistent surveillance alternative.

In an anonymized sample includes people who might be missed in other clinical data, such as those without health insurance who may avoid going to the doctor and those who don't have the resources to get tested or don't feel like doing it.

It's also scalable, which is critical for the country's chronically under-resourced public health system, according to Ghaeli. She claims that testing a wastewater system that serves 100 million people is much less expensive than clinically testing each individual.

She said that wastewater treatment facilities were quick to get started, whereas public health departments were a little slower – and funding was a big factor.

Partnerships with research institutions, such as North Carolina's with the University of North Carolina, aided many early adopters of wastewater surveillance.

Wastewater data may not currently play a formal role in federal guidance, but making the data public removes a barrier to it continuing to play a role in the conversation.

Source : CNN