Largely empty campuses haven’t prevented Covid-19 cases from springing up among students at MIT and Harvard. Here a student traverses seating at Harvard Stadium in Allston. (Photo: Ron Gilbert via Flickr)

New Covid-19 cases among Cambridge residents climbed to 48 on Tuesday, bringing the total in the past two days to 92 infections. That increase would have been unheard of last week and far exceeds new cases in most of the spring surge.

Harvard University and Massachusetts Institute of Technology students and staff who are considered residents of Cambridge accounted for 20 of the 48 new cases on Tuesday, or 42 percent, according to the Cambridge Public Health Department Covid-19 dashboard. Counting all students and staff, not just Cambridge residents, both universities have reported increasing new cases on their own dashboards.

City officials didn’t address the big jump in cases on Monday or Tuesday, and there was no Covid-19 update at Monday’s meeting of the City Council. Several councillors asked for a return to weekly updates at which city manager Louis DePasquale, chief public health officer Claude Jacob and police commissioner Branville G. Bard Jr. present the latest news and answer questions from councillors.

The latest test results followed the pattern this fall of young people accounting for most of the cases. Over the past two days, teens and children make up 15 of 92 cases; people in their 20s make up 39 cases; and those in their 30s make up 12 cases.

On Monday the mayor and vice mayor pleaded for shutdowns of indoor dining and other indoor commercial activities, saying the rising caseload would force schools to close under the metrics adopted by the School Committee. The measure asking that the city manager meet with surrounding communities to coordinate a response was blocked by councillor Tim Toomey, who exercised his right to table the order until the next council meeting, Monday.

Arguing for the order, vice mayor Alanna Mallon said one of the metrics, the average number of new cases over seven days, was almost at its limit of 25 new cases; the metric actually measures the average number of new cases per 100,000 population, which was 20.7 as of Tuesday, according to the schools – still uncomfortably close, but not almost at its limit.

A second metric, the percent of positive tests, is artificially low in Cambridge because college students and staff as well as many residents are getting repeated tests, which depresses the ratio. As of last week, it was 0.3 percent, compared with the schools’ limit of 5 percent. A more accurate picture of positive test results, the percent of individuals testing positive, was 4.9 percent for viral tests – the kind most Cambridge residents get – as of the most recent city report, for the week of Nov. 8. It has been rising.

The third metric, the amount of virus in sewage samples, far exceeded the School Committee limit, but that could change as Cambridge begins to test wastewater from the city rather than using measurements from Massachusetts Water Resources Authority sewage collected from much of Eastern Massachusetts.

If two metrics exceed the limits the schools must shut down in-person teaching.