The U.S. Centers for Disease Control and Prevention (CDC) actively monitors the Covid situation around the country and worldwide following the recent surge in cases in China.

Its newest effort to take extra caution amid the spike involves testing wastewater from airplanes as concerns continue to grow over travelers from China.

The National Association of County and City Health Officials CEO Lori Tremmel Freeman said Wednesday that the US CDC has “done some very preliminary work” to carry out wastewater testing with airlines.

“I think they’ve done some early piloting of one flight, for example, testing the blue water in one flight,” she was quoted as saying by CNN.

Freeman noted that the program could be expanded to include retrieving samples of wastewater from multiple flights or a single airport for COVID-19 testing.

“So they’re looking at that, and it does require some agreements to be made with the airlines and so forth – and then how and when to do this – but it does look like a promising area of surveillance for the future. Certainly, expanding the wastewater surveillance just is another data point that can be helpful, and it’s a less-intrusive way of doing disease surveillance,” Freeman said.

It wasn’t clear which airline participated in the initial phase of the program. But United Airlines has been in touch with the national public health agency, telling CNN that it’s still “evaluating our participation” in the program.

Before 2022 ended, the CDC announced it would require travelers flying to the U.S. from China to present negative COVID-19 test results within two days before boarding their flights due to the latest surge in the Asian giant.

The requirement started to be implemented on Thursday in airports with flights to the U.S. based in the People’s Republic of China and the Special Administrative Regions of Hong Kong and Macau.

On the same day, the World Health Organization (WHO) called out China for allegedly “under-representing” the true impact of the disease in the country by changing its definition of COVID-19 death to only include patients who succumbed to respiratory failure due to the viral infection.

Within two weeks since the change, Chinese officials only reported fewer than 20 Covid deaths because patients who tested positive for SARS-CoV-2 before and after dying due to other complications were not counted.

The Chinese government has also insisted that its COVID-19 data is transparent despite releasing significantly low official figures amid the alarming surge in cases in the country.