Maine reported 519 new cases of COVID-19 on Friday as the BA.2 omicron subvariant continues to drive up infection rates across the Northeast.

The seven-day average of new cases in Maine rose to 310 Friday, a nearly 50 percent increase in less than a week. The average daily case number had slowly increased to about 200 over the past few weeks before the uptick this week. The state reported 605 new cases of COVID-19 on Wednesday, the highest one-day total since March 4.

As the daily case count rises, more Maine counties have been reclassified as having a moderate risk of virus transmission and increased hospitalizations.

The five northern and eastern counties of the state – Aroostook, Piscataquis, Penobscot, Washington and Hancock – now are in the moderate risk category, according to the U.S. Centers for Disease Control and Prevention. The other 11 counties remain in the low-risk category.

Last week, Aroostook was the only Maine county not considered to be at low risk.

Residents of moderate risk counties are advised to wear masks when indoors if they are at high-risk of complications from COVID-19 because of their age or underlying health conditions. There is no official masking recommendation in low-risk counties.

The low-risk designation does not mean the virus is not circulating in that county. It indicates the level of transmission and rate of hospitalizations are not expected to place a strain on local hospitals.

The rise in cases coincides with increasing levels of the virus in wastewater samples in many parts of the state. Levels have risen in York, Brunswick, Lewiston-Auburn and Bangor, while remaining fairly stable in Portland and Augusta, according to the Maine Center for Disease Control and Prevention.

The number of hospitalized patients stood at 101 Friday, up one from the day before. No additional deaths were reported.

The number of patients with COVID-19 has so far held steady in Maine and the Northeast despite a rise in infection rates in recent days and weeks.

While hospitalization increases always follow weeks behind any rise in infections, many experts have said high levels of immunity in the United States should prevent another major surge of hospitalizations from the BA.2 variant.

Of those hospitalized Friday, 18 were in critical care and four were on ventilators.

Since the pandemic began, Maine has recorded 239,649 cases and 2,276 deaths.

The number of new cases reported by Maine and other states has always understated the actual number of infections because not everyone who gets the virus gets a test. But the daily case reports now represent a more significant undercount because of the increased reliance on at-home tests, which are not included in official reports.

That growing gap between actual infections and reported cases means case counts can’t be directly compared to other points in the pandemic. However, the data is one indicator of how infection rates are changing and where they are rising the fastest.

New cases have begun rising nationwide, with the Northeast recording the most significant spike.

Maine had the seventh highest infection rate in the United States as of Wednesday, with 133 cases per 100,000 residents over the previous seven days, according to the U.S. Centers for Disease Control and Prevention. The national infection rate is 62 cases per 100,000 people. Vermont, Washington, D.C., Rhode Island, New York,  Massachusetts, New Jersey had the six highest infection rates.

Maine’s rate of positive tests also has increased over the past several weeks, indicating a higher level of community spread of the virus. Seven percent of test results statewide on Wednesday were positive, according to the Maine CDC. The positive test rate had dropped to 3 percent in March after peaking at more than 20 percent during the omicron wave in January.

Walgreens also tracks the positivity rate for tests performed at its pharmacies. Of the nearly 700 tests performed at Walgreens pharmacies in Maine last week, 22 percent came back positive, up from 14 percent the previous week, the company said.