One wastewater coronavirus number ticks down, while another continues to march higher

Coronavirus testing in Lawrence last weekend.Erin Clark/Globe Staff

The amount of coronavirus traces found in wastewater coming from the northern section of the MWRA system, which includes Boston, dipped slightly, while the numbers from the southern section continued to rise to new heights.

Both sections have surpassed the levels that were detected during the springtime surge, according to data posted by the Massachusetts Water Resources Authority. The data, which state officials are monitoring for signals of where the pandemic is headed, reflected tests conducted up to Thursday.

The pilot program looks for SARS-CoV-2 RNA copies per milliliter of wastewater. People shed the virus in their stool and it travels downstream to the treatment plant. Officials are hoping the tests can serve as an early warning system for virus surges.

Cambridge-based Biobot Analytics, which conducts the testing, says it has found that the amount of virus in the wastewater is correlated with newly diagnosed coronavirus cases 4 to 10 days later.

“Hey Boston - wake up - we’re in trouble here,” Joseph Allen, a professor at Harvard T.H. Chan School of Public Health and director of the school’s Healthy Buildings Program, tweeted Friday morning, including the MWRA’s chart of the indicators, which shows both the springtime surge and the current surge, which has outpaced it.

Hey Boston - wake up - we're in trouble here.

[This graph shows the levels of virus detected in wastewater data from the greater Boston area, thru 12/8.] https://t.co/gqpDWnQzSx pic.twitter.com/AzRobknRe3

— Joseph Allen (@j_g_allen) December 11, 2020