The levels of coronavirus detected in Eastern Massachusetts waste water, an important indicator of the prevalence of COVID-19 infections, shot up sharply in recent days.
Officials say waste water data from the Massachusetts Water Resources Authority can be an early warning signal, detecting COVID-19 infections before people get tested and the tests are officially reported.
The numbers have become even more crucial as more people are using rapid, at-home tests that don’t get reported and reflected in official case counts.
The latest waste water data posted by the MWRA covered samples taken up until Monday. The numbers had been fluctuating for several months, but began rising on Sept. 21.
“This uptick is concerning as wastewater sampling is our best leading indicator for transmission,” Andrew Lover, an assistant professor of epidemiology in the School of Public Health and Health Sciences at the University of Massachusetts Amherst, said in an e-mail. “However, we’ll need another few sampling days to see if the trend continues before making any firm conclusions.”
Waste water from 43 communities, including Boston, converges at the MWRA’s Deer Island plant on Boston Harbor for treatment before being piped miles into the ocean. The sewage is tested for traces of the deadly virus. The MWRA reports numbers for both the southern and northern sections of its system. The testing determines the number of SARS-CoV-2 RNA copies per milliliter of waste water.
The northern MWRA section saw five days of increases. The seven-day average count reached 1,016 copies/mL of the virus on Monday. The number had been as high as 1,273 on May 17 during a spring bump in infections. But it had been as low as around 100 in March during a lull after the winter’s devastating Omicron surge.
In the southern section, the seven-day average count rose over the same five-day period, ending at 993 copies/mL on Monday. The number had gone as high as 1,332 on May 17. In March, it had dropped into the low 90s.
Experts have said they expect COVID-19 to make a comeback this fall and winter, but it likely won’t be as bad as the past two years because it will be blunted by the immunity people have built up from previous infections, vaccinations, and updated boosters. One caveat, however, is that a new variant could change the game significantly.
Other Massachusetts COVID-19 metrics such as total cases and hospitalizations are not showing spikes right now, though there has been a recent increase in cases among children and teenagers. The Department of Public Health’s next weekly data release will come out Thursday.
Matthew Fox, a professor of epidemiology and global health at the Boston University School of Public Health, said the wastewater numbers suggest that “cases are going up pretty quickly.”
“But given our levels of immunity in the population through prior vaccination and through prior infection, it’s too early to say that this is going to lead to a lot of hospitalizations. Right now they are stable. I think we can expect they will go up as cases go up but the hope is they don’t go up dramatically. That’s what I’ll be watching out for,” he said in an e-mail.
Boston health officials said Friday they were seeing upticks in COVID-19 transmission and hospitalizations, and urged residents to get the new Omicron-specific booster shot.
Material from prior Globe stories was used in this report.
Martin Finucane can be reached at firstname.lastname@example.org.