Home Covid tests are in supply at a Cambridge pharmacy. (Photo: Marc Levy)

The city’s count of Covid-19 cases, steadily rising again because of a new, more contagious variant, might be higher yet if there was more testing and if all home test results were reported to health authorities. This month the city cited lower demand when it reduced free walk-in tests to one day a week while continuing to offer tests by appointment every day with partner CIC Health. Another major test provider, the Massachusetts Institute of Technology, made testing optional for staff on Feb. 21 and students on March 14.

Less testing in laboratories where results are reported and more use of home tests make case counts less reliable. The Institute for Health Metrics and Evaluation at the University of Washington School of Medicine estimates that only 7 percent of daily infections in the United States are now being reported. Some scientists worry that incomplete counts could hurt efforts to respond to the pandemic.

The Cambridge Public Health Department believes there is enough testing. “At this juncture we are not overly concerned that there is inadequate testing/testing capability within Cambridge,” spokesperson Dawn Baxter said Thursday. At the remaining testing sites “there continues to be demand,” she said. The city is watching the percentage of tests that are positive, Baxter said; it has been rising.

Every week the state health department reports the number of PCR tests performed within each city and town over the previous two weeks. The figures show that the two-week total in Cambridge dropped sharply in January after the omicron peak and continued to decline until reaching bottom in the second half of March – after MIT made testing optional for students. Since then the total has risen slowly.

Cambridge has reported that cases among university employees and students who live in the city account for a substantial portion of the city’s case count. In the first week of April “higher ed made up 41 percent of cases in Cambridge, with the other 59 percent coming from the [non-university] community,” Baxter said.

Harvard and MIT

Harvard University “represented a little over 70 percent of the higher ed cases,” Baxter said. Harvard, though, still requires students and staff to be tested once a week. Baxter said health officials have no way to estimate whether required testing at Harvard contributes to that 70 percent figure.

The requirement also means that Harvard can report a lower positivity rate than the city, because individuals are tested repeatedly and must test whether they have symptoms or have been exposed to the virus. “That said, required testing means more testing, and more testing likely identifies asymptomatic cases that would otherwise go undetected,” Baxter said, referring to university surveillance testing in general and not just Harvard.

The university will eventually drop that requirement for people without symptoms, The Harvard Crimson reported April 13, based on an interview with university president Lawrence Bacow. Bacow didn’t provide a date. Meanwhile, cases there began rising in February, fueled by infections in undergraduates. Harvard College tightened restrictions, and cases fell.

Graduate students started getting infected in greater numbers last month, pushing up the total. Case numbers have remained high, with more contribution from undergrads again.

MIT, meanwhile, is also reporting rising numbers but doesn’t disclose the number of tests. Unlike Harvard, MIT is not reporting its positivity rate because those who choose to get tested are more likely to be infected and because fewer people are getting tested, the university said.