Samples from US wastewater sites have shown an increase in the coronavirus this month in a third of locations, said the Centers for Disease Control and Prevention, suggesting that cases in key cities including New York are rising.

The rise in the virus that causes COVID-19 was detected in wastewater samples collected from March 1-10, the CDC's COVID-19 data tracker showed. Thirty-six percent of samples from wastewater sites showed an increase in the presence of the virus, according to Bloomberg. That was more than twice the levels reported from Feb 1-10.

The CDC confirmed on Tuesday that there had been an increase in the virus in wastewater samples. But COVID-19 cases remain relatively low across the United States when compared with the same time last year. At least 81 percent of US citizens have received at least one dose of a COVID-19 vaccine. That's led several cities including New York and Los Angeles to drop mask mandates.

Data from the CDC shows that between Feb 26 and March 12, out of 398 wastewater sites collecting data, 44 saw an increase of at least 10 times of the virus, and 62 sites saw an increase of more than twice the levels recorded in the prior period.

Wastewater samples provide important, advanced information about the spread of the coronavirus because those who are infected shed the virus in their feces. The agency added wastewater data to its COVID-19 tracker on Feb 4.

CDC Director Rochelle Walensky said during a White House news briefing on Feb 9: "This is a powerful tool that, when paired with traditional public health surveillance, can help us identify where the disease is spreading and how best to distribute resources."

John Dennehy, a professor of biology at Queens College of the City University of New York, researches virus evolution, ecology and emerging viruses in new host populations.

Dennehy told China Daily: "In cities with sewers, everyone contributes to the wastewater, thus wastewater provides an unbiased snapshot of SARS-CoV-2 prevalence."

But the increase of the virus detected in the samples comes amid fears that a new coronavirus variant, BA.2, could be more virulent than the Omicron variant.

BA.2 made up 23.1 percent of the variant spreading in the US as of March 12 in the US, the CDC said.