Deer Island digester tanks process sewage from 61 communities. Cambridge says it is now testing sewage within the city instead for a more accurate sense of local coronavirus issues. (Photo: Eric Kilby via Flickr)

As the city reported 30 new cases of Covid-19 Thursday, the largest daily jump since the spring, officials also announced that the program to test Cambridge sewage for the virus has begun. The wastewater analysis could give health officials advance knowledge of outbreaks – earlier than testing results – and might point to individual areas where infections are occurring.

Update on Nov. 14, 2020: On Friday, the city reported 33 new cases of Covid-19; on Saturday, the city reported 25 new cases of Covid-19, bringing the city to 147 within a seven-day period.

The sewage testing program calls for weekly samples to be collected at three locations that cover wastewater from the entire city. The city’s announcement didn’t say when sampling began or is planned to begin, or if the city has already received results from Biobot, the company doing the analysis. Biobot is also analyzing sewage at the Massachusetts Water Resources Authority’s Deer Island treatment plant, which receives wastewater from much of Eastern Massachusetts.

According to the announcement, the city will disclose the results to the public “in the coming weeks.” Cambridge Public Health Department spokeswoman Susan Feinberg didn’t immediately respond to an email seeking more specifics.

Meanwhile, the School Committee held a special meeting Thursday to consider using the new Cambridge-specific wastewater results as one of its metrics that decide whether in-person learning can continue in public schools. The district now looks at Deer Island testing that includes 61 communities – and other metrics the district uses to assess coronavirus dangers are either statewide or encompass all of Suffolk and Middlesex counties, which holds some 2.4 million people. In each instance, the district would switch to looking at data from within Cambridge.

Among younger residents

The 30 new cases – which brings the city to 89 within a five-day period – follow the pattern since the summer lull of young people showing the highest infection rate. Of the 30 residents who tested positive, 29 were under 40. Six were in the youngest age group, 19 and under; 16 were in their 20s; and seven in their 30s.

The total included four new cases among Harvard University students and staff who live in Cambridge, and two new infections in Massachusetts Institute of Technology students and staff. Hult International Business School, with one to four cases previously, now has five cases.

The sharp rise in Cambridge cases means that the city now has an average infection rate of 8.9 confirmed cases per 100,000 population over the past two weeks, up from five cases per 100,000 for the previous two-week period and 3.9 cases per 100,000 in the period before that. The figures come from the state Department of Public Health, which still categorizes the city as “green” or low-risk under new metrics adopted last week.

The latest rate validates city councillor Quinton Zondervan, who said Monday that the infection rates reported weekly by chief public health officer Claude Jacob are outdated and make Cambridge look better than it is. Jacob, who provides the state figure from the previous week at his council presentations on Mondays, acknowledged that it is dated. Zondervan had said his own calculation showed a rate of nine cases per 100,000 on Monday, close to the state’s rate reported Thursday.

Among older residents

Cases have not increased in the city’s long-term care facilities since Oct. 26, when the city announced that a resident of an assisted living center had tested positive, bringing the total to 274 cases. The city didn’t name the place, but other sources indicated it was Neville Place at Fresh Pond. Earlier in October, there were seven new cases among residents and one in a worker at Sancta Maria Nursing Facility, also unnamed by the city but identified from other sources. The city included only five of the Sancta Maria cases in its total because the other two residents had been discharged to another community, and the worker did not live here.

In addition, one employee at Cambridge Rehabilitation & Nursing Center has tested positive recently, and one to four workers at Youville House Assisted Living were newly reported as infected on Nov. 5-6. None of these cases are included in the city’s total, because the employees are not Cambridge residents.

Update on Nov. 16, 2020: Nicole Breslin, chief executive and president of Youville House, said Monday that no Youville House staff had tested positive. She said she was unaware of the state reports and would correct them. The state Department of Public Health says the data in the daily posts are “self-reported” – in other words, reported by the long-term care facilities.

Reports to the U.S. Centers for Disease Control and Prevention say two Cambridge nursing homes, Cambridge Rehabilitation and Sancta Maria, had empty beds early this month: Sancta Maria reported 117 occupied beds out of 134 and Cambridge Rehabilitation, 65 beds filled out of 83. Neville Center, the third Cambridge nursing home, has reported data to the CDC, but the federal agency has not posted it because it says the information failed a quality audit.

The number of Covid-19 patients in the hospital has risen steadily statewide. The Cambridge Health Alliance has 21 patients in its two hospitals in Cambridge and Everett, spokesman David Cecere said Thursday. That is far below the census during the spring surge, but the number has been increasing this fall. Cecere has said the health care system is operating normally and has been preparing for a second surge.