Coronavirus waste water numbers have nearly tripled just three weeks after dropping to their lowest levels in two years, suggesting that cases of COVID-19 are ticking up in the greater Boston area.
The Massachusetts Water Resources Authority regularly tests waste water from Boston’s Deer Island Treatment Plant for traces of the virus that causes COVID-19. The testing determines the number of coronavirus RNA copies per milliliter of waste water, as shed by people with and without symptoms.
The latest seven-day averages, through July 18, show that Boston and areas to the north reached 278 copies per milliliter of waste water, and areas to the south of Boston reached 255 copies per milliliter of waste water, up from a low of 82 and 91 copies, respectively in late June. On Monday, the numbers hit levels not seen since March before dropping slightly.
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However, it is too early to know whether this is a significant uptick, experts said.
“No major shifts in the variants that are circulating in the area offer an obvious explanation,” said Dr. Jeremy Luban, a professor at UMass Chan Medical School. “More likely it reflects people’s behavior.”
As the summer continues, many have abandoned preventive measures, creating a higher risk for infection.
“Since the end of the public health emergency was declared, many people are downplaying their symptoms and many more have stopped masking, even at large events,” said Dr. Cassandra Pierre, associate hospital epidemiologist and medical director of public health programs at Boston Medical Center and assistant professor at Boston University’s Center for Emerging Infectious Diseases.
The weather could also be a factor in the rising number of infections, Pierre said. As showers and thunderstorms poured down on Massachusetts over the last two weeks, many folks have been forced to remain inside and opted to host large indoor events.
Although elevated waste water numbers sometimes precede increases in COVID-19 hospitalizations, experts believe the rising levels will not translate to severe cases right now.
“Our understanding of the correlation between the waste water numbers and people who need to be hospitalized has changed a lot in the last year,” said Dr. Paul Biddinger, chief preparedness and continuity officer for Mass General Brigham.
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“We have not seen many severe cases,” he said. Across all 16 Mass General Brigham hospitals, only eight patients are currently hospitalized due to COVID-19, he said. Statewide, hospitalizations have continued to drop. On Thursday, the state reported a seven-day average of 102 COVID-19 hospitalizations, down from 113 the week before.
However, experts say that we should still be wary of the coronavirus.
“We have a lot of vaccine- and infection-derived immunity, which may mean that there may be a lot of asymptomatic transmission that’s happening at this moment,” said Pierre.
Therefore, experts recommend taking preventive measures, including avoiding crowds and indoor activities, and testing for COVID-19 when experiencing symptoms.
For people who are at higher risk of infection, however, experts recommend masking out of an abundance of caution and keeping an eye on exposure risk.
Being fully vaccinated also decreases the chances of severe complications from COVID-19, Pierre said. The general public should be aware of the most recent CDC guidelines, which call for everyone age 6 and up to get an updated bivalent booster.
“I think each person needs to make their own risk assessment,” said Biddinger, “Though we are hopeful that the clinical coronavirus cases will remain very low, we want people to protect themselves and take all the steps necessary to avoid infection.”
Material from Globe wire services was included in this report.
Emma Obregón Dominguez can be reached at emma.obregon@globe.com. Follow her on Instagram @eobredom.