The death toll from confirmed coronavirus cases in Massachusetts rose by 19 to 9,342, the Department of Public Health reported Wednesday. The number of confirmed cases climbed by 509, bringing the total to 133,868.
State officials also said Boston remained in the high-risk category for coronavirus on Wednesday, as Mayor Martin J. Walsh announced that city schools will delay the start of in-person learning for the next phase of students because of the city’s rising positivity rate.
Boston is one of 40 cities and towns designated high-risk, meaning they have had more than 8 cases per 100,000 residents in the past 14 days, the Department of Public Health reported in its weekly community data set.
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The city’s average daily rate of infection per 100,000 residents was at 10, the department said.
Another 20 communities remained in the red zone: Attleboro, Avon, Chelsea, Dracut, Everett, Framingham, Haverhill, Lawrence, Lowell, Lynn, Marlborough, Methuen, Middleton, Nantucket, New Bedford, North Andover, Revere, Springfield, Winthrop, and Worcester.
And 19 cities and towns were newly designated as high-risk on Wednesday: Acushnet, Amherst, Brockton, Chelmsford, Dudley, Dartmouth, Holyoke, Hudson, Kingston, Leicester, Malden, Plymouth, Randolph, Southborough, Southbridge, Sunderland, Waltham, Webster, and Woburn.
Only two towns — Holliston and Lynnfield — dropped out of the high-risk category.
Middleton remained high-risk one week after officials reported an outbreak of the virus at the Middleton Jail and House of Correction. On Wednesday, the Essex County Sheriff’s office said testing of all inmates at the jail was complete and 139 had tested positive, though nearly three quarters were asymptomatic. Thirty-three staff members also tested positive.
State officials also reported that 16,134 more people had been tested for coronavirus, bringing the total to more than 2.34 million. The number of tests administered climbed to more than 4.47 million. New antibody tests had been completed for 286 people, bringing that total to 121,906.
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The seven-day average rate of positive tests, which is calculated from the total number of tests administered, remained at 1.1 percent for a ninth consecutive day. The lowest observed figure for that metric — a number watched closely by state officials — is 0.8 percent.
The state also offers another measure of test positivity: daily positive tests per people tested, which some specialists have suggested is a better measure of the pandemic. That number stood at 3.2 percent, its lowest rate since Sept. 27.
Meanwhile, the three-day average of hospitalized coronavirus patients grew slightly from 468 to 494 in Wednesday’s report. The lowest that metric has been is 302.
The number of hospitals using surge capacity grew from four to five, and the three-day average of deaths from confirmed cases remained at 13 for a second day, after hovering at 15 for the two previous days; the lowest that number has been is nine.
Jeremy C. Fox can be reached at jeremy.fox@globe.com. Follow him @jeremycfox.