Confirmed COVID-19 infections among Massachusetts residents younger than 20 are higher than they have been through the entire pandemic, prompting one leading expert to say the rising caseload is likely a reflection of increased testing and another to warn it could forecast a wave of transmission in older adults.

While some communities are backing away from in-person learning amid a statewide increase in cases, the infection rate among the state’s youngest age group has grown more rapidly in the past two months than any other cohort. Officials have been consistently pointing to unsafe behavior among young adults as driving a significant portion of the uptick.

Between Oct. 5 and Oct. 18, the Department of Public Health recorded 1,914 new cases of the highly infectious coronavirus among residents between the ages of 0 and 19, more than in any of the seven other age groups, according to data published Thursday.

That figure is higher than any two-week sum for the state’s youngest residents since March, a News Service analysis found, an unusual record that no other age groups — all of which saw far more substantial spikes in the spring — mirrored.

Several experts said the trendline for children and teenagers does not warrant sounding the alarm, pointing to the expanded access to testing and noting that hospitalizations and deaths have remained virtually flat alongside rising case numbers.

Dr. Lloyd Fisher, president of the Massachusetts chapter of the American Academy of Pediatrics, said the new levels of positive tests among the youngest is “a good thing,” describing it as evidence that the public health apparatus is catching cases and responding with contact tracing and isolation.

“In the past, we weren’t testing the mildly symptomatic or asymptomatic kids,” Fisher said. “We were only testing the really sick kids. So we’re not seeing more sickness, we’re just seeing more positives.”

Massachusetts General Hospital Center for Disaster Medicine Director Paul Biddinger, also an MD, struck a more concerned tone.

The reasons behind the increase in pediatric COVID cases could be partly tied to increased testing, he said, but “in any age range, rising case numbers are of concern.”

“On top of that, in other parts of the country, when we’ve seen case rates rise among younger populations, two to four weeks later, we see case rates rise in older populations,” Biddinger said. “One of the significant worries is whether this is a harbinger of increasing illness in older adults who do need hospitalization, intensive care unit care, and unfortunately do experience death at higher rates as well.”

Thursday’s weekly data report was the first time in DPH records that the 0-to-19 range counted the most new cases out of all age groups.

Adjusted for population, the infection rate was higher among four other groups covering ages from 20 to 59. But that metric, too, shows fastest growth among the youngest: the infection rate per 100,000 people has tripled since mid-August for ages 0 to 19, while for all other groups it has multiplied roughly two to two and a half times.

Higher numbers of recorded cases have not coincided with more hospital admissions or fatalities among the youth. Two-week sums of new hospitalizations continue to hover in the single digits for the youngest group, several times lower than any other age range, while the DPH has only counted two COVID-related deaths among children and teenagers since April.

Another issue is the group’s range: unlike most of the age ranges tracked by DPH that count a single decade, the lowest tier counts two decades, from newborns up to 19-year-olds, so it is unclear if a subset such as college students is disproportionately lifting up the cohort’s totals.

Much of the increase has taken place at the same time that many K-12 school districts welcomed students back for partial or full in-person learning. Some districts, including Boston Public Schools, have reversed course and shifted to all-remote learning amid rising statewide case counts.

Experts interviewed by the News Service offered a range of opinions on the overlap between schools and young COVID infections.

Biddinger said there is not yet sufficient data to determine if students returning to school has affected transmission, while both Fisher and MGH infectious disease specialist Dr. Sandra Nelson said they believe the available evidence indicates that education is not directly driving infections.

“If schools were driving transmission, we would see a disproportionate increase in cases in younger adults, the 5-to-17 age range, relative to cases in the rest of the state,” Nelson, who has served as a medical adviser to the state focusing on education since June, said. “What we’re seeing is rates in the 0 to 19 (range) are increasing in parallel with rates elsewhere.”

By contact tracing backwards from confirmed cases, experts have found many infections among children were likely contracted after a family member was exposed rather than at school, Fisher said.

The state Department of Elementary and Secondary Education’s data also does not indicate widespread infections in schools, Fisher and Nelson said.

“Almost all of the cases in schools are one case here and there,” Nelson said. “They’re not reporting multiple cases or evidence of clusters, and the only clusters that have been reported generally have been attributed to out-of-school activities.”

Many colleges and universities in Massachusetts have offered testing to their students and faculties, sometimes several times per week, but the same options are often not made available to public school families.

Gov. Charlie Baker has aimed his focus in recent weeks on young adults, warning this week that those between 19 and 39 represent “where the vast majority of the increase in positive tests has been happening.”

Much of the uptick, he argues, is linked to individual behaviors such as hosting or attending large gatherings and disregarding public health precautions, rather than the resumption of business activities or in-person schooling.

“The real-life experience and the research with respect to schools is overwhelming at this point that schools are not spreaders,” Baker said Thursday when asked about Boston’s decision to go remote. “The kids in schools are not spreaders of COVID.”

He declined to “Monday morning quarterback” the decision by city officials, then again stressed that “people are not finding schools, K-12 schools, to be a big issue with respect to spread.” Baker said the 150-plus cases linked to public schools in Massachusetts come from a pool of “hundreds of thousands of people,” representing a low positive test rate.

Fisher, who has also communicated with the Baker administration to offer his insight, said DPH should work to break down case numbers by age groups in each community, which would offer a clearer indication whether any spikes are related to school or other causes.

His recommendation: prioritize education as the “first to open and the last to close” through the course of the pandemic.

Without in-person learning, Fisher said, children face enormous risks of negative mental and social health impacts. Experts have already observed an increase in depression, anxiety and suicidal ideation among young children, and the harm could be disproportionate on English language learners or families with essential workers for whom child care is difficult to obtain.

“We could be causing really significant harm to the future of this generation, especially for underserved populations,” he said. “I’m very worried, and we all are, about the impact on our vulnerable populations.”

State officials reported 202 new cases of COVID-19 in Massachusetts public schools this week, including 129 among students engaged in-person and hybrid learning models. The other 73 cases reported to the Department of Elementary and Secondary Education were among school district staff with building access. The total case number in the department’s Thursday evening report was up from last week’s 92 student and 68 staff cases.

The education department this week began including in its case report the total number of people who are accessing public school buildings, saying the 129 COVID-positive students came from approximately 450,000 who are attending in-person school at least some of the time, and the 73 staff cases were among a workforce pool of roughly 75,000.