Boston officials urge more residents to get COVID-19 tests. Experts say that message applies to the whole state

William Soto leaned back as registered nurse Kelly Hogan tested him for the coronavirus at a site in Dorchester.Jessica Rinaldi/Globe Staff

Amid Massachusetts' rising COVID-19 cases comes a new concern: a drop-off in new tests in Boston, a city at high risk for community spread.

Boston’s weekly count of residents who were tested for the first time declined nearly 50 percent over a month-long period, data provided by the Boston Public Health Commission shows. The decline, which officials attribute to “COVID fatigue,” has prompted city leaders to urge more residents to seek testing, even if they think they are low-risk — advice scientists say all Commonwealth residents would be wise to follow.

“People have done an amazing job within Boston of trying to do what they need to do to keep each other and their families safe, and part of that is getting tested,” said Marty Martinez, chief of health and human services. “We’re trying to remind folks that everyone should be tested, regardless of symptoms. Unless you’re in complete isolation, there is risk for most people.”

The number of confirmed coronavirus cases in the state climbed by 1,137 on Wednesday, bringing the total number of cases to 150,498, and the death toll from confirmed cases rose by 36 to 9,700, the Department of Public Health reported. Boston has seen 19,986 confirmed cases over the course of the pandemic and 778 deaths, the city’s public health commission reported.

But at the same time that risk is rising, testing in Boston seems to be slipping.

Recent health commission testing counts show a clear downward trend from a mid-September high. At that point, about 20,000 people were tested each week, but between Oct. 13 and 19, just 11,056 people sought testing for the first time. During the same period, the percentage of people testing positive has gone up, reaching 7.8 percent this week.

“The bottom line is that we need more residents to consider getting tested, and make it a regular part of their routine. It gives people a peace of mind while informing their decisions — as well as informing us at the city of future steps in response and recovery," Mayor Martin J. Walsh said in a statement.

Martinez said the health commission’s method for measuring testing is “conservative.” The city only counts first-time test-seekers because it wants to keep the tens of thousands of routine test-takers — such as college students and hospital employees, who are tested frequently, but are usually negative — from skewing the data. Still, half of Boston residents have never been tested for COVID-19, Martinez said. Combined with the fact that the city’s testing centers are not reaching their daily capacity, he said, it is clear that the decline in testing is real and concerning, and even those who have been tested before might need to be tested regularly.

“Whatever regular interactions happen with people, you potentially are exposing yourself,” Martinez said, adding that going to work, attending small gatherings with friends, and traveling are risks that people tend to underestimate. Anyone who does any of that should get tested, he said.

“We know that people can get COVID and have no symptoms, or can even spread it before they’re symptomatic, so it’s really really important that getting tested is something that everyone does,” he said.

Boston lists 22 testing sites on its website, with additional mobile sites available in some neighborhoods on a rotating basis. Visits generally come at no cost to insured people who have symptoms, and mobile sites provide free testing to anyone, regardless of whether they have insurance or feel sick.

Martinez said that several sites have far more testing capacity than demand. With the long waits and lab supply shortages of the spring mostly past, he attributed the drop-off in testing to exhaustion with the pandemic.

Epidemiologists said that keeping close watch of cases is important to controlling COVID-19 throughout the state, not just in Boston.

A number of metrics — daily new cases, data showing traces of COVID-19 in wastewater, and a rising proportion of positive tests — point to a rising level of infection in Massachusetts. Seventy-seven communities are on the state’s list of high-risk cities and towns, and reported cases have topped 1,000 the past several days, levels not seen since May.

“If anything, we need to be testing more,” said Dr. David Hamer, a Boston University epidemiologist and physician at Boston Medical Center. “We need to be aggressive about testing and identifying infected individuals so we can separate them from others they might infect, and trace their contacts.”

Experts said extensive testing is important because it empowers officials — and ordinary people — to stop outbreaks before they start. If people know early on that they have been infected, they can self-isolate, inform contact tracers of others they may have infected, and contribute to the data that helps state officials determine what types of settings are high risk.

“The only tool we have besides mask-wearing and social distancing is testing-tracing-isolation-quarantine,” said Samuel Scarpino, a Northeastern University epidemiologist. It is an approach that has worked well for universities in the Boston area, as well as a number of countries around the world that have kept cases from ballooning out of control.