In crush of data and analysis, one key is missing: Who is getting tested?

A person got tested for coronavirus at the Stanley Street Treatment and Resources in Fall River.Barry Chin/Globe Staff/The Boston Globe

As Massachusetts reopens its economy, local health officials are tracking coronavirus infections for signs of trouble, wading through spreadsheets that chart new infections, deaths, and people who thankfully have recovered.

But in the flood of metrics about this pandemic, one key measure is often missing: Most Massachusetts cities and towns are not routinely told how many people in their communities have been tested for the virus.

“That’s actually the biggest data gap that we have and something that we think is really important for us to have access to at the local level,” said Sharon Cameron, Peabody’s health and human services director. “I think many communities have been communicating to the state that it’s a big need for us.”

Local health officials in Quincy, Watertown, Lexington, and beyond have voiced similar concerns. Without the data, officials say, they are unable to fully gauge the prevalence of the virus in their community and ensure everyone has equal access to testing. Test numbers also help put new infections in context: 10 positive results out of 20 tests carry a different meaning than 10 positives out of 1,000.

Governor Charlie Baker’s administration does release a daily figure for the number of people tested statewide, reporting Tuesday that 4,920 more new tests had been performed. That increased the total since January to 545,481 or 8 percent of the state’s population.

But that statewide number does not indicate whether the tests come from people living in densely populated cities or rural towns, from people who live in nursing facilities or single-family homes.

Hours after this story was published online Tuesday night, state health officials said they would begin publishing on Wednesday data regarding the total number of tests and positivity rate for each city and town, according to an e-mail from Department of Public Health spokeswoman Ann Scales. The Globe had first requested the information May 11.

The Baker administration has made testing data a key component of health metrics guiding the state’s reopening. The top indicator is a seven-day, rolling statewide average of the percentage of tests that come back positive. This measure is often called the positivity rate — and the statewide average has been dropping.

Public health experts cautioned against relying too heavily on a statewide positivity rate because testing availability and demographics can vary dramatically from the Berkshires to the fishing docks of Gloucester. While the seven-day rate could offer a broad overview of progress, it has limitations and needs to be viewed in conjunction with hospitalizations, deaths, and other metrics.

There's going to be a temptation to hunt for that "silver metric," the one above all others that indicates it's safe to reopen, but the Baker administration is wisely considering a broader array of indicators, said Dr. Ranu Dhillon, an instructor at Harvard Medical School who specializes in the management and response to epidemics.

The World Health Organization has advised governments that before reopening the positivity rate should remain below 5 percent for at least 14 days. In Massachusetts, that measure has trended consistently downward but has never been under that 5 percent benchmark. Johns Hopkins University’s Coronavirus Resource Center noted Monday that Massachusetts’ positivity rate of 9.1 percent made it one of 29 states that did not meet the criteria.

Dhillon suggested — as the World Health Organization recommends — that Massachusetts should focus on a 14-day positivity measure because symptoms of COVID-19 can take up to two weeks to appear after someone is exposed. The state’s current seven-day average may not capture percolating infections, especially as new sectors of the state reopen, he said.

The state also should be carefully monitoring positive rates among different demographic groups, Dhillon said, because that rate can swing dramatically depending on the pool of people tested.

"Communities of color and those who have been marginalized typically are the places we have seen more cases, or more cases having bad outcomes," Dhillon said. "That's important in this epidemic … and if you aren’t measuring it, you won't know what's happening around it.”

In Massachusetts, the state routinely notifies local boards of health that they have new COVID-19 cases in their community, with details available in the state’s infectious disease database. But there is no easy way for local officials to determine the number of people who have been tested in their communities, according to a spokesperson for the state Department of Public Health.

The state is working to address the issue, according to the spokesperson, who added that cities and towns can ask the state to run a report tallying the total. Boston, for example, has received the data on a regular basis. Still, the data lack key demographic information about who is getting tested.

Earlier this month, the town of Norwood made a request and received the total number of tests since the start of the pandemic, which showed that the town has a positivity rate of 24 percent, according to the Norwood public health director, Sigalle Reiss. That rate was slightly higher than the comparable statewide figure at the time, but there was not enough context to calculate the recent trend, Reiss said.

The result is that, in the race to assess the impact of public health actions, cities and towns are only receiving half of the data needed for measurement. Local officials need both figures — the number of positive cases and the total number of people tested in their community, said Cindy Prins, an associate professor of epidemiology at the University of Florida.

"If you are in an area with limited testing, your 10 positive cases may be hiding more widespread transmission than you realize," Prins said.

Biostatistician Helen Jenkins of Boston University said in an e-mail that instead of a statewide positivity rate, it was "more useful to break those metrics down by age group or county, for example, to get a better understanding of what is really happening.”

Several other states provide significantly more information to the public and its local health departments. New York State’s COVID-19 tracker showed, for example, that Sunday in the Bronx there were 110 positive results among the 2,445 people tested. Rhode Island’s data center includes a breakdown for each city and town, showing Sunday that 16 percent of the population in Central Falls had been tested.

Illinois goes even further, publishing an interactive ZIP code map that shows a breakdown of testing data by age, gender, and race.

In Massachusetts, there has been a struggle to obtain better testing data, according to the health department spokesperson, who noted that a person’s address and other personal information isn’t always submitted to the state.

That lack of information can hamper municipalities such as Watertown, where the public health director, Larry Ramdin, doesn’t know how many people in his town are tested each day for COVID-19. And Ramdin doesn’t know how many are infected are hospitalized.

If he had these two pieces of data, Ramdin said, he would be able to better understand and manage the risks of infection in his community.

Lexington’s health director, Kari Sasportas, said she has been so swamped trying to stay ahead of COVID-19, that she hasn’t had the chance to ask the state for more complete data about testing in her town. But information about who is — and is not — able to get tested in Lexington would be helpful.

"It allows us to think about whether … we are targeting the response and intervention to the right population,” Sasportas said. “And are we mobilizing our resources to the right places.”