The Massachusetts Institute of Technology and other schools have brought back students in depressed numbers during the coronavirus pandemic. (Photo: alist via Flickr)

The Massachusetts Institute of Technology and other local universities have begun conducting Covid-19 tests on a vast scale as their students return to campus. During four days last week, MIT performed a total of 6,598 tests of students and staff. Three people tested positive on Wednesday, the school reported.

At Boston University, 7,676 tests between Aug. 15 and Friday produced 14 positive results; another 62 were invalid and must be redone, the university said. Northeastern University said one person tested positive out of 5,080 tests during four days last week. Harvard University, where about 1,600 undergraduates, mostly first-year students, and 200 graduate students are expected to move in starting next week, does not yet report testing results publicly but intends to do so, a spokesman said Monday.

It’s not known how much of the MIT testing has been reported on state or Cambridge coronavirus websites. For example, on Wednesday, the institute said it performed 1,839 tests of which three were positive. The city dashboard reported no increase of cases between Tuesday and Wednesday. The state daily report of the number of Cambridge residents tested gave a total of 816 on Wednesday, less than half the number of tests the institute reported, though some of its tests could have been repeats.

One big unknown in reporting is that Cambridge says it counts only infected people with a city address, and college students may have off-campus housing in a city near Cambridge or be listed by an address in their hometown. Vice mayor Alanna Mallon has asked the health department to disclose the number of positive cases at Cambridge colleges; chief public health officer Claude Jacob said he would consult with his staff.

The large-scale testing programs at campuses will continue during the fall semester because the universities plan to test on-campus students and staff repeatedly to identify outbreaks. The repeat testing is necessary because the “gold standard” tests the institutions are using, PCR tests that look for fragments of the coronavirus, show only whether people are infected on the day they get tested; someone could test negative one day and be positive and capable of transmitting the virus the next day.

Harvard and MIT tests are being analyzed at the two universities’ affiliated research center, the Broad Institute. Its high-speed laboratory can handle 35,000 samples of Covid-19 a day and is giving test results to scores of colleges and universities. In the past week, the Broad Institute has stepped up the number of samples it’s processing in a big way: Between Aug. 18-21 the institute handled 114,120 tests, or an average of more than 28,500 a day. During the previous four days the average was 11,490 tests a day. Turnaround time is less than two days.

The state is also using the institute to test samples from residents of hot spot communities where case rates are highest, and previously sent tests of nursing home and assisted living residents and staff to the Broad.

And in Cambridge, the institute analyzes samples from the Public Health Department’s free testing program at locations in North Cambridge, The Port and now expanded testing slots in East Cambridge.

While college students get access to repeated tests – because they’re required – others throughout the state complain of limited availability and long waits for results. The Cambridge health department has been opening up appointments by the week in July and August and slots available online have often disappeared within a few days. As of Saturday there were few times available in The Port on Wednesday and a week after; none in North Cambridge; and many open at the new location at the King School in East Cambridge. Results are available from the Broad Institute within 36 hours, officials have said, but people may wait longer to hear from the department.

It’s not known how much it costs to process tests at the Broad Institute. The Massachusetts Senior Care Association, which represents nursing home and assisted living operators, offers Broad Institute processing for $60 a test to its members.