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UPDATED May 29: YourArlington continues to report a running tally of Covid-19 incidence regionally based on wastewater analysis by Biobot Analytics. These figures are in reverse chronological order toward the end of this ongoing column, along with an explanation of why most scientists consider wastewater analysis statistics to be valuable data.

This information may be of greater meaning now in mid-2023, as major organizations including many Massachusetts hospitals are ceasing universal masking mandates -- and many other measures of what is no longer officially a pandemic soon may no longer be kept at all.

Based on readings taken May 24, 2023, Middlesex County, where Arlington is located, is down from the week prior, to 306, making it probably the second-highest in the commonwealth, second only to Barnstable County's 406, though with Franklin and Hampshire not yet posting updated numbers. Currently the national average is 186.

All the numbers cited here represent Covid-19 virus concentration per mililiter of wastewater; however, this is not the same as the total number of Covid-19 infections, which is near-impossible to know. 

As of the May 24 reading, the other numbers were Berkshire, 221; Bristol, 180; Essex, 181; Hampden, 143; Nantucket, 202; Plymouth, 136; Suffolk, 219; and Worcester, 188. 

In broad terms, historically, Covid numbers tend to be lower in warmer months, when people are more likely to be outside, and higher in colder months, when people spend more time together indoors. The longest stretch of high numbers recently in Middlesex County ran from Nov. 30, 2022, through Jan. 18, 2023. The county's weekly number has now been in triple digits for more than four months.

All current results commonwealth-wide are relatively low especially compared with highest totals statewide since the pandemic began in mid-March 2020 -- in some cases nearing the five-digit range and notably exceeding the national average at that time -- in late December 2021 through early January 2022.

Biobot Analytics is a relatively new, female-led, Cambridge, Mass.-based firm that samples and analyzes wastewater nationwide. Biobot tests, analyzes and reports Covid-19 data for all 50 states except for Michigan; statistics are also listed for the District of Columbia and the U.S. Virgin Islands. 

Throughout the United States, Biobot reports numbers county-by-county within each state, displaying them graphically and comparing them to the U.S. average for each week. All the counties in Massachusetts are monitored; however, this is not necessarily true of every state.

For some localities, the percentage of known variants of the virus for a given week are also shown.

The list of weekly reported numbers for Middlesex County, starting with Nov. 9, 2022, is given further down in this article.

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 probably 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 contend that other Covid-19 statistics, being primarily based on public testing sites, physician notes and hospital records, may be significantly undercounting the true total number of infections, especially as asymptomatic individuals rarely are accounted for. This is because people with 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. 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 U.S. states save Michigan; these graphs also compare each monitored county to the national picture for the same timeframes. One may choose to see the charts/numbers for the past six weeks, the past six months or overall for the past three-plus years.

Recent numbers to date for Middlesex County, Mass., per Biobot Analytics are as follows: 


May 24, 2023: 306

May 17, 2023: 447

May 10, 2023: 211

May 3, 2023: 236

April 27, 2023: 386

April 19, 2023: 223

April 12, 2023: 258

April 5, 2023: 420

March 29, 2023: 387

March 22, 2023: 366

March 15, 2023: 588

March 8, 2023: 438

March 1, 2023: 435

Feb. 22, 2023: 542

Feb. 15, 2023: 678

Feb. 8, 2023: 881

Feb. 1, 2023: 774

Jan. 25, 2023: 890

Jan. 18, 2023: 1,118

Jan. 11, 2023: 1,461

Jan. 4, 2023: 1,879

Dec. 28, 2022: 2,452

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 running column by YourArlington Assistant Editor Judith Pfeffer was first published Jan. 7, 2022. It was updated Jan. 9 to change the headline for greater accuracy and updated Jan. 10 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 to post the latest available weekly number and to include at the end a paragraph from a state website describing the scientific importance of wastewater analysis. It has since been updated Jan. 19, Jan. 26, Feb. 3, Feb. 10, Feb. 17, Feb. 25, March 1, March 10, March 17, March 27, April 3, April 9, April 17, April 21, April 27 and May 5, 2023, with the latest data reported publicly by Biobot Analytics of Cambridge, Mass. The text was corrected May, 6, 2023, to give the current national average rate, and May 9, 2023, to report results for four commonwealth counties whose numbers were not posted as soon as those of the other eight. The column was updated most recently May 14, 2023, May 22, 2023, and May 29, 2023.