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UPDATED Feb. 3: YourArlington continues to report weekly a running tally here of statistics of Covid-19 incidence regionally, listed in reverse chronological order.

A portion of text from a government website, quoted at the end of this column, suggests that numbers are regarded as more meaningful when considered over several weeks rather than in any given week.

These numbers typically are posted each Thursday evening,  based on the previous day's results, by Biobot Analytics, a relatively new, female-led Cambridge-based firm that samples and analyzes wastewater nationwide. Throughout the United States, Biobot reports numbers county-by-county, including for Middlesex County, where Arlington is located.

YourArlington aims to update this list by 6 p.m. Friday each week.

The numbers represent virus concentration per mililiter of wastewater; however, this is not the same as the number of Covid cases in the county, which is difficult to know currently. Based on numbers as reported Feb. 3, 2023, the numbers for Middlesex County have trended down for the past five weeks.

The list of weekly reported numbers, starting with Nov. 9, 2022, is given farther down in this article. Over the past three months, the second half of December 2022 had the highest numbers.

As of August 2022, the Town of Arlington no longer routinely tested for Covid-19 nor compiled statistics about local infection rates, making Biobot’s information likely the best currently known, most understandable and publicly available. Many mainstream experts consider analysis of wastewater to be a particularly good metric because samples are anonymous, involuntary and universal.

Many mainstream experts also contend that other statistics, because they are primarily based on public testing sites, physician notes and hospital records, may be undercounting the true total number of infections, especially as asymptomatic individuals rarely are accounted for. This is because people with near-non-existent, mild or moderate symptoms of possible Covid-19 sometimes cannot or will not seek medical attention, cannot or will not use nasal-swab-based home tests, or cannot or will not report their positive test results to authorities.

Biobot’s home page demonstrates the national picture, including a graph showing the Northeast having generally outpaced the rest of the nation for more than a year so far.

This page if one scrolls down a bit and looks to the left side can be used to show the graphs and numbers for all 12 counties in Massachusetts. 

Recent numbers to date for Middlesex County are as follows:


Feb. 1, 2023: 732

Jan. 25, 2023: 887

Jan. 18, 2023: 1,063

Jan. 11, 2023: 1,353

Jan. 4, 2023: 1,841

Dec. 28, 2022: 2,344

Dec. 21, 2022: 2,145

Dec. 14, 2022: 2,411

Dec. 7, 2022: 1,417

Nov. 30, 2022: 1,347

Nov. 23, 2022: 867

Nov. 16, 2022: 771

Nov. 9, 2022: 695

A page from the website of the Massachusetts Department of Public Health explains the significance of wastewater analysis as follows: "The amount of virus that a person has in their stool and the length of time that they have virus in their stool varies. Because of this, the amount of virus measured in wastewater does not tell us the total number of cases in an area and does not tell us the amount of increase or decrease in cases in communities. However, if the amount of virus in wastewater increases or decreases over several time points, that information shows that cases are either increasing or decreasing in the community. Importantly, wastewater data can provide an early warning about increasing cases, since virus will show up in wastewater several days, maybe even a week, before positive test numbers start to increase."


Jan. 6, 2023: Majority at town public schools wear masks, complying with ‘strong recommendation’


This runing column by YourArlington Assistant Editor Judith Pfeffer was first published Saturday, Jan. 7, 2022. It was updated Jan. 9, 2023, to change the headline for greater accuracy, and updated Jan. 10, 2023, to state what Biobot Analytics measures, to note that the weekly list is presented toward the end of the article and to provide additional context. It was updated Jan. 12, 2023, to post the latest available weekly number and to include at the end a paragraph from a state website describing what scientists see as the significance of wastewater analysis.It was updated Jan. 19, 2023, Jan. 26, 2023, and Feb. 3, 2023, with the latest data posted by Biobot Analytics.