Monday’s announcement that the Maine Center for Disease Control and Prevention is scaling back case investigation and contact tracing is not likely to have a dramatic impact because COVID-19 already has become so widespread.

“To be honest, you can’t really do contact tracing when you have a huge amount of transmission,” said Robert Horsburgh, an epidemiologist at Boston University. “It’s a very good strategy for tamping down an epidemic that hasn’t gotten started. Once it’s widespread, it’s less useful. A lot of people simply have no idea where they are being infected.”

As of Monday, the CDC said it will investigate and contact trace only people younger than 18 or 65 and older, health care workers and first responders, those who are hospitalized, those with disabilities, people living or working in congregate living facilities, and individuals associated with schools or childcare facilities.

Many other states have made similar moves, including New Hampshire last month.

Maine CDC Director Dr. Nirav Shah had been saying for weeks that despite rapidly rising case numbers, contact tracing remains a valuable tool and he was reluctant to throw in the towel. He reiterated that message Monday and said the state will continue to bring on new employees and use its resources to track the most vulnerable populations.

But Shah also acknowledged a hard truth: The state simply doesn’t have the ability to keep up with the increased volume. Every positive test requires work by the CDC to ensure that it is indeed a new case. The recent surge has created a backlog of more than 4,000 tests for the first time since the pandemic began.

“The sustained increase in numbers of new cases and new lab reports has outpaced the CDC’s approach that has taken us to where we are right now,” Shah said at a media briefing.

Those who test positive for COVID-19 and are not in the targeted categories will still be notified by state officials, but they will be asked to reach out to possible contacts themselves. Previously, a CDC contact tracer would work with the individual to identify where they might have become infected and to list their contacts so the CDC worker could call them.

Stephen Kissler, a post-doctoral researcher in immunology and infectious diseases at the Harvard T.H. Chan School of Public Health, agreed with Horsburgh’s assessment that the shift is not surprising.

“You certainly lose the ability to stop clusters of infections as they arise and prevent them from spreading further,” he said. “But with so much spreading in community, you reach a point of diminishing returns.”

Kissler said he’s encouraged Maine will continue to investigate and trace vulnerable populations.

“Although we probably haven’t seen huge benefits on the scale of the whole population, in local communities, it can be different,” he said. “There are still benefits to contact tracing in health care facilities, schools, nursing homes.”

Still, asking some people to be their own contact tracers could be a burden.

“You hope people who test positive are doing their due diligence already,” Kissler said. “But with no real regulations and not much public health messaging, it could be a lot to ask.”

For most of the summer and early fall, Maine avoided widespread community transmission. That all changed in late October. Total cases have more than doubled since then and the seven-day average stood at 291 per day on Monday after a record-setting 427 cases were announced. There were more deaths in November, 67, than any other month and more than the previous five months combined. Hospitalizations are at an all-time high as well.

There has been a dramatic shift since the spring that shows younger people – often the most likely to be asymptomatic – are being infected at a much higher rate. On May 1, people under the age of 30 represented 13.2 percent of the total COVID-19 cases in Maine. On Dec. 1, that age group made up 31.5 percent of the total. Conversely, people over the age of 70 made up 26 percent of the total number of cases on May 1. By Dec. 1, they represented 13.5 percent of the total.

Still, individuals over the age of 70 are far more likely to die from the virus. Of the 227 deaths reported so far, 193, or 85 percent, of individuals have been 70 or older.

Since the pandemic began, Maine and other states have been using contact tracing and case investigation to identify people who have come into contact with confirmed cases. Those individuals have then been asked to isolate until no longer infectious to avoid spreading the virus further. Contact tracing has long been a tool in public health to monitor and limit disease spread and has been used for outbreaks of tuberculosis, smallpox, syphilis and, more recently, to mitigate the spread of the Ebola virus in West Africa in 2014.

When the pandemic first reached Maine, the Maine CDC had 15 contact tracers and case investigators. The number gradually increased to more than 100 by the fall and now stands at 135, with another 80 currently in training. A report in April from the National Association of County and City Health Officials said each state should have 15 contact tracers per 100,000 people during normal times. During a pandemic, the rate should double to about 30 per 100,000 people.

Maine has 1.3 million people, which means it would need between 200 and 400 contact tracers based on that calculation.

Politifact, the fact-checking arm of the Tampa Bay Times, reported in October that many states were having challenges with contact tracing. Problems such as delays with testing and major case surges have impeded this work, but a bigger issue has been lack of community buy-in. Not enough people were participating. There also has been some suggestion that not everyone who tests positive is being forthright about all their possible contacts.

“People are having too many contacts,” Horsburgh said. “The virus can’t spread without contacts.”

He said contact tracing is a valuable epidemiological tool, but the nature of COVID-19 has made it more challenging than normal.

“So much is spread by people who are not symptomatic,” he said. “The whole idea is that you have a sick person, you can go to them and find out who they interacted with before and after. If people aren’t presenting as sick, you don’t have anyone to go to.”

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