Category: Community Testing

This is another update that breaks down case and testing statistics by city and town in Massachusetts based on data published in the state’s weekly public health report. In the original community spread post https://www.masscoronavirus.net/community-spread-in-massachusetts-september-26-2020/ I outlined some of the issues with the community data in the weekly report, and described my methodology for calculating how a particular city and town has contributed to the change in either case incident rates or test positivity rates in the state.

 

Table 1: Highest Case Incidence Rates and Contribution to Case Incidence Increase
Period Ending November 14, 2020
Highest Case Incidence Rates				Largest Contributors to Weekly Case Incidence Increase
City/Town	14 Day Case Count	Daily Case Rate per 100,000		City/Town	14 Day Case Count	Daily Case Rate per 100,000	% Contribution
Norfolk	204	116.6		Boston	3058	31.5	9.7%
Lawrence	1328	108.1		Worcester	1014	37.8	4.9%
Fall River	1078	86.2		Lowell	1044	64.2	4.2%
Tisbury	49	83.9		Springfield	1117	51.1	4.1%
Marion	50	77.7		Lawrence	1328	108.1	3.7%
Shirley	85	71.2		Fall River	1078	86.2	3.5%
Chelsea	358	69.3		Lynn	869	61.6	2.7%
Swansea	147	65.8		Cambridge	273	17.4	1.6%
Everett	443	65.2		New Bedford	548	39.2	1.5%
Lowell	1044	64.2		Peabody	289	36.9	1.4%
Total/State	28660	29.4		Total/State	28660	29.4	37.4%

 

Statewide case incidence rates have more than tripled from four weeks ago when I wrote my last update, highlighting the rapid spread of covid throughout Massachusetts during that time.  The list of communities with the highest incidence rates is varied:

(1) relatively small towns such as Tisbury and Marion,

(2) previously identified hotspots such as Lawrence and Lowell,

(3) and communities with large institutional complexes such as the prisons at Norfolk and Shirley. The state has stopped putting asterisks on those communities in the weekly report – a notational change it started several weeks prior.

Overall, only 31 of the 351 communities in the Commonwealth had no cases in the two weeks ending November 14, and only 34 communities have seen a decrease in cases from the previous report.  The largest community with no cases is Provincetown, population about 2,600. 

95% of the state’s population lives in communities which would have been labeled as red zone under the original labeling  guidelines that were relaxed last month.  This is up from 71% just two weeks ago. I noted this labeling change and calculated its impact in a post about two weeks ago (https://www.masscoronavirus.net/massachusetts-reporting-change-november-6-2020/ ). 

As I’ve indicated in prior posts, the communities having the largest impact on the week over week increase in the statewide incidence rate tend to be either very large (e.g., Boston), have had large increases in cases (almost all), or both.  The smallest community on the list is Peabody, population of about 56,000.  Note that only Cambridge has a incidence rate below the statewide average.

 

Table 2: Highest Positivity  Rates and Contribution to Positivity Rate Increase
Period Ending October 17, 2020
Highest Test Positivity Rate				Largest Contributers to Weekly Positivity Rate Increase
City/Town	14 Day Test Count	Test Positivity Rate (%)		City/Town	14 Day Test Count	Test Positivity Rate (%)	Relative Impact (%)
Lawrence	13,003	13.0%		Boston	205,995	1.7%	8.8%
Shirley	817	11.3%		Worcester	46,820	2.4%	4.7%
Tolland	9	11.1%		Lowell	13,408	8.8%	4.7%
Fall River	11,807	10.9%		Springfield	19,188	7.1%	4.1%
Norfolk	2,077	10.0%		Fall River	11,807	10.9%	3.7%
Westport	1,434	9.3%		Lawrence	13,003	13.0%	3.5%
Lynn	11,253	9.1%		Lynn	11,253	9.1%	3.0%
Swansea	1,893	8.9%		Cambridge	50,947	0.6%	1.6%
Lowell	13,408	8.8%		Peabody	6,740	4.8%	1.5%
Somerset	1,938	8.6%		Everett	6,368	8.3%	1.5%
State	1,088,469	3.0%		Total/State	1,088,489	3.0%	37.2%

 

Table 2 focuses on testing statistics throughout the state.  The communities with the highest positivity rates for the last two weeks are similar to those with the highest case incidence rates, since raw testing figures tend to correlate highly with population (95% correlation for testing over the past two weeks).  The one notable exception is Tolland, which had 1 positive case and 9 tests, resulting in a positivity rate of 11.1%.

The ten communities with the largest impact on the statewide positivity rate increase are the same as the communities with the largest impact on the statewide case incidence increase with one exception – Everett has replaced New Bedford. But Everett was 11th on the case incidence list, and 10th here, so this is not a big change.

 

 

This is a follow-up to the first post documenting how the coronavirus has differentially impacted communities in Massachusetts, using the state’s weekly public health report for data. That post https://www.masscoronavirus.net/community-spread-in-massachusetts-september-26-2020/ described some of the issues with the weekly report, as well as my methodology for calculating how a particular city and town has contributed to the change in either case incident rates or test positivity rates in the state.

Table 1: Highest Case Incident Rates and Contribution to Case Incidence Increase
Period Ending October 17, 2020
Highest Case Incident Rates				Largest Contributors to Weekly Case Incidence Increase
City/Town	14 Day Case Count	Daily Case Rate per 100,000		City/Town	14 Day Case Count	Daily Case Rate per 100,000	% Contribution
Middleton*	89	61.6		Boston	1166	12.0	6.2%
Lawrence	567	45.9		Lynn	244	17.3	5.0%
Chelsea	150	28.4		Revere	230	27.0	4.2%
Revere	230	27.0		Gloucester	77	19.2	3.6%
Everett	159	23.4		Lawrence	567	45.9	3.5%
Kingston	41	21.6		Brockton	202	14.7	2.7%
Webster	49	20.4		Chicopee	76	9.5	2.2%
Marlborough	121	19.9		Saugus	71	17.8	2.1%
Acushnet	29	19.8		Methuen	136	18.1	1.9%
Gloucester	77	19.2		Wakefield	59	15.6	1.8%
Total/State	8980	9.2		Total/State	8980	9.2	33.2%

The three left hand columns focus on the communities with the highest per capita case incident rates for the two-week period ending October 17.  The state did make one change to the report, adding an asterisk to communities to indicate where some of the cases are institutional and not directly attributable to the local community.  A municipality has an asterisk if it has a long-term care facility, a higher-education facility, or a correctional facility that (1) has had more than ten cases in the past fourteen days, and (2) these cases are more than 30% of cases in the community over the past fourteen days.  In the case of Middleton, at the top of the list, Middleton House of Corrections has had a large covid outbreak.

The four right hand columns focus on the communities which contributed the most to the increase in the statewide case incidence rate.  As I discussed in the prior post, communities on this list tend to be either large in population (e.g., Boston, which is on the list because of its size), or have had a very large change in case incidence (e.g., Gloucester and Saugus, both with populations of abut 30,000).  Boston’s case incidence rate increased by about 8%, but Gloucester’s rate almost tripled. The case incidence rate increased statewide from 8.7 cases to 9.2 cases per 100,000 population per day.

The last column in Table 1 shows the percentage contribution of each community to the statewide increase. This column emphasizes that the case increase has been distributed widely across the state, rather than concentrated in just a few communities.

Table 2: Highest Positivity  Rates and Contribution to Positivity Rate Increase
Period Ending October 17, 2020
Highest Test Positivity Rate				Largest Contributers to Weekly Positivity Rate Increase
City/Town	14 Day Test Count	Test Positivity Rate (%)		City/Town	14 Day Test Count	Test Positivity Rate (%)	Relative Impact (%)
Buckland	21	23.8%		Boston	173,409	0.8%	6.7%
Middleton*	1,273	8.9%		Lawrence	9,175	8.2%	5.9%
Lawrence	9,175	8.2%		Lynn	7,399	4.3%	5.6%
Revere	6,238	4.7%		Revere	6,238	4.7%	4.3%
Berkley	395	4.3%		Gloucester	2,953	2.8%	4.3%
Everett	4,580	4.3%		Brockton	8,417	3.0%	3.5%
Lynn	7,399	4.3%		Chicopee	4,090	2.3%	2.5%
Chesterfield	74	4.1%		Wakefield	2,816	2.6%	2.4%
Methuen	4,520	4.0%		Methuen	4,520	4.0%	2.1%
New Bedford	5,687	4.0%		Saugus	2,694	2.9%	2.0%
State	885,959	1.24%		Total/State	885,959	1.24%	39.2%

The left three columns in Table 2 focus on the communities with the highest test positivity rate.  There are some surprising names on the list, in particular Buckland and Chesterfield.  This is because they have high positivity rates with very limited testing – Buckland had five positive cases in the two weeks ending October 17, and Chesterfield  had three.  These are hardly hotspots.  However, four of the top ten communities for case incidence rates are also in the top ten for test positivity rates.

The right-hand columns focus on the communities making the largest contribution to the statewide positivity increase from 1.17% to 1.24%.  Boston tops this list as well, even with a very small increase in test positivity from 0.74% to 0.8%, because of its large volume of testing.  In the two weeks ending October 17, almost 20% of testing in Massachusetts was in Boston.  In contrast, Gloucester and Saugus are not large testers, but each had test positivity rate increases of about 1%. The communities driving the increase in case incidence are also driving the increase in test positivity – the top ten communities in Table 1 and Table 2 are the same.

 

What a day, as we learn Trump tested positive for the coronavirus. No further comment is necessary on that. But here’s a trivia question for you. Over the two week period ending September 26, what Massachusetts community had the highest per capita Covid testing rate? Stop. Before you read on, think about it. Is it Chelsea, or Everett, or Lowell, or another one of the hot spot communities in Massachusetts? Is it Boston, because of the many medical centers located there? No.

As Table 1 shows, the big winner is Williamstown, home to Williams College.  More than 4% of Williamstown’s population is being tested each day for coronavirus.  Of course, this figure is somewhat distorted, as many of those tested are presumably students who are not included in Williamstown’s stated population.  But even if one assumes that all of Williams College’s students (about 2,000) were back on campus, the per capita testing rate is astounding.

And there was even more testing being done in Williamstown for the two weeks ending September 19th, as it had the largest dropoff in testing from week to week.  In all, nine of the top ten per capita testing communities are home to college and universities. And even Somerville’s inclusion might partially reflect testing associated with Tufts. (In the original version of this post, I had stated that Dudley was a outlier, because I didn’t realize that it is home to Nichols College, which has done extensive testing.  Thanks to Jen for pointing out the error).

 

Table 1: Per Capita Massachusetts Testing Statistics
Most Testing and Largest Testing Changes
Week over Week Ending September 26,2020
Two Weeks Ending 9/26/20			Weekly Change Ending 9/26/20
City/Town	Daily Tests per 100,000		City/Town	Largest Increase in Daily Tests Per 100,000		City/Town	Smallest Increase in Daily Tests Per 100,000
Williamstown	4,211		Southborough	431		Williamstown	-796
Amherst	3,856		Cambridge	421		Nantucket	-105
Cambridge	2,622		Newton	401		Somerset	-10
Wellesley	2,328		North Andover	379		Charlton	-8
Somerville	2,103		Boston	282		Peabody	-7
North Andover	1,968		Somerville	263		Yarmouth	-4
Norton	1,944		Dedham	259		Rowley	-2
Boston	1,845		Brookline	250		N. Attleborough	4
Dudley	1,806		Wellesley	196		Wrentham	5
Waltham	1,684		Chelsea	158		Westport	6

 

One technical point. It is possible, although unlikely, that there are communities in Massachusetts with higher testing rates than shown here. Why? I am using population estimates that are embedded in the weekly report itself (it can be derived from the daily incident rate and the number of cases). But if there are fewer than five cases, the state suppresses the exact number, so I can’t derive a population estimate. In fact, of the 351 communities in Massachusetts covered in the report, I can’t calculate a population for over half. I could try to pull population estimates from other sources and integrate them into this analysis, but I think it highly unlikely this will add any community to the top ten list (and I’m lazy).

One other point related to the blog itself. As I noted when I first started, I’ve never blogged before. I’m learning as I go. And I noticed yesterday’s post via email, on a tablet, or on cell phone has strange formatting or the numbers weren’t visible through the colors. I am trying to learn how better to format the posts, but for now, if you flip your device to landscape mode, the posts become more readable (and I’ve bolded the numbers within colored cells).

As the Covid case rate and test positivity rate in Massachusetts begin to climb once again (albeit in a much more gradual and controlled fashion compared to the beginning of the outbreak), it is important to understand whether the increase is driven by just a few “hot-spot” communities or more widely distributed throughout the Commonwealth.  Fortunately, the state issues a weekly report that provides case rate and testing positivity information for each city and town within the state.

There are several issues with the report.  First, while it is issued weekly, it provides information for the trailing two weeks, so it is not possible to directly discern weekly trends (as a new week is added, an old week drops off).  Second, by the time the report is published on Wednesday evenings, it is a bit stale, as it contains information only up to the prior Saturday.  Nonetheless, it is what is available.

I’m concerned here with changes in case rates and changes in test positivity, not the absolute levels.  To do so, I look at the two week data published in the most recent report compared to the data in the report issued one week prior.  The rolling two week nature of the report can make the conclusions from this analysis misleading and mask short-term trends.  For example, if a really bad week rolls off the report, and is replaced with a more stable week, it can look as though trends are improving in a particular community when they really aren’t.  But this analysis can certainly provide insight, especially over the longer term.

The report includes new cases and case rates per 100,000 over the prior two weeks.  For the state in aggregate, the case rate is just the weighted average of the case rate in each community in the state, where the weights are equal to the population in that community divided by the population of the state.  Therefore, the change in the state case rate is just the weighted average of the case rate change in each community (with the population-derived weights).

We can then rank communities by their impact on the state case rate change by looking at the product of their case rate change and their population-derived weight.  What does this tell us?  A community is likely to be at the top of the list if (1) it is relatively large, or (2) it has had a relatively large change in case rates, either positive or negative.  Smaller communities with relatively stable case rates have little impact on the overall state figures.  In contrast, Boston, which has about 10% of the state’s population is likely to be at the top of the list even with small changes in its case rate.  Table 1, which shows the top ten biggest contributors to the increase in the state case rate, illustrates this point.

 

Table 1: Top Ten Contributors to Massachusetts Case Incidence Increase
Rolling Two-Week Case and Incidence Rates
Week over Week Ending September 26,2020
	Two Weeks Ending 9/19/20		Two Weeks Ending 9/26/20
City/Town	14 Day Case Count	Daily Case Rate per 100,000	14 Day Case Count	Daily Case Rate per 100,000	% Contribution
Springfield	95	4.3	183	8.3	6.3%
North Andover	26	6.1	111	26.2	6.1%
Haverhill	52	5.6	129	14.0	5.5%
Boston	773	7.9	825	8.5	4.0%
Lowell	129	7.9	179	10.9	3.6%
Lawrence	273	22.1	313	25.4	2.9%
Methuen	59	7.9	94	12.5	2.5%
Plymouth	27	3.1	48	5.5	1.5%
Amherst	3	0.5	24	4.2	1.5%
Burlington	4	1.0	21	5.4	1.2%
Total/State	4823	4.9	5569	5.7	35.0%

 

Both Boston, with a relatively small increase in cases rates, and Amherst, with a population of about 40,000, are in the top ten negative contributors.  However, Amherst has had a significant case increase, presumably from an outbreak associated with UMass.  Note that all the communities in Table 1 moved up one color zone in the state’s three-tier color-coding system, with the exception of Lawrence, which was already in the red zone.

The last column is a measure of the percentage impact each community had on the state’s case rate increase.  The primary takeaway is that the impact is widely dispersed among these communities – there are not a few new “hot-spots” driving the case rate increase.

Table 2 is the equivalent report, but focused on the communities which have contributed the most to a decrease in the state’s case rate.  Because the overall rate is increasing, the impact on the overall rate is significantly smaller for these communities.  Also, only three of them (Newton, Somerville, and Wrentham) shifted down a color zone.  Newton had barely been in the yellow zone to start.

Table 2: Top Ten Contributors to Massachusetts Case Incidence Decrease
Rolling Two-Week Case and Incidence Rates
Week over Week Ending September 26,2020
	Two Weeks Ending 9/19/20		Two Weeks Ending 9/26/20
City/Town	14 Day Case Count	Daily Case Rate per 100,000	14 Day Case Count	Daily Case Rate per 100,000	% Contribution
Newton	52	4.0	33	2.6	-1.4%
Chelsea	118	22.4	99	18.8	-1.4%
Lynn	160	11.3	143	10.1	-1.2%
Framingham	130	12.5	116	11.1	-1.0%
Worcester	238	8.9	224	8.3	-1.0%
Nantucket	42	26.5	30	18.9	-0.9%
Somerville	53	4.9	41	3.8	-0.9%
Hingham	25	7.5	14	4.2	-0.8%
Brockton	92	6.7	82	6.0	-0.7%
Wrentham	19	12.0	11	7.0	-0.6%
Total/State	4823	4.9	5569	5.7	-9.7%

 

The state also provides testing counts and positivity rates by community.   Here, the state provides the data for the lower “all testing” positivity rate (which it has been emphasizing since mid-August), not the individual case positivity rate.  The testing positivity rate was essentially unchanged between the two reports. The statewide positivity rate is just a weighted average of each community’s positivity rate, but the weights are now the number of tests for each community divided by the total number of tests.  Also, unlike population-based weights, the weights for each community can vary from report to report as testing counts change.

 

Table 3: Top Ten Contributors to Massachusetts Test Positivity Increase
Rolling Two-Week Test and Positivity Rates
Week over Week Ending September 26,2020
	Two Weeks Ending 9/19/20		Two Weeks Ending 9/26/20
City/Town	14 Day Test Count	Test Positivity Rate (%)	14 Day Test Count	Test Positivity Rate (%)	Relative Impact (%)
North Andover	6,730	0.40	8,335	1.43	11.4%
Springfield	10,714	1.10	11,488	1.92	11.3%
Haverhill	3,732	1.77	4,466	3.27	9.2%
Methuen	3,237	2.41	3,745	2.99	3.1%
Lowell	6,785	2.24	7,196	2.71	3.0%
Plymouth	2,474	1.21	2,919	1.75	2.2%
Burlington	1,457	0.41	1,616	1.42	2.1%
Amherst	21,102	0.05	21,862	0.12	1.9%
Middleton	421	1.43	529	3.78	1.7%
Webster	1,087	0.28	1,197	1.34	1.6%
State	693,958	0.86%	782,320	0.87%

 

The communities dominating the positivity rate tables are either those with large changes in positivity rates or those performing many tests.  Table 3 shows the top ten contributors based on increases in the positivity rate.  For example, Amherst, which has a very low positivity rate, is a very big tester relative to its population presumably because of UMass.  It is testing at almost eight times the rate of Springfield.

Table 4 shows the top ten communities contributing to a decrease in positivity rates.  Boston is on this list, even with a very small positivity rate decrease, because of its large number of tests (almost 23% of the state total for the last two weeks).  This might appear to contradict the inclusion of Boston as a top ten contributor to an increase in the case rate in Table 1.

However, it does not.  First, case rates and test positivity rates are measuring different things (case rates focus on individuals and test positivity rates are just measuring tests including repeat testers).  Second, the increase in the case rate in Boston can easily be a result of increases in newly tested individuals (impossible to discern from this report), as overall testing increased by 18% from one period to the next.   In other words, there can be both increases in case rates and decreases in positivity rates if more testing is being done.

Table 4: Top Ten Contributors to Massachusetts Test Positivity Decrease
Rolling Two-Week Case and Incidence Rates
Week over Week Ending September 26,2020
	Two Weeks Ending 9/19/20		Two Weeks Ending 9/26/20
City/Town	14 Day Test Count	Test Positivity Rate (%)	14 Day Test Count	Test Positivity Rate (%)	Relative Impact (%)
Lynn	5,641	4.11	6,068	3.33	-8.5%
Worcester	34,906	0.86	36,092	0.79	-7.6%
Chelsea	3,858	4.02	4,690	2.75	-6.6%
Revere	4,636	4.31	5,031	3.82	-4.8%
Boston	152,051	0.60	179,475	0.56	-4.7%
Newton	14,336	0.44	19,485	0.21	-4.4%
Framingham	4,426	3.32	5,511	2.49	-4.1%
Brockton	5,324	2.27	5,623	1.97	-3.6%
Somerville	19,717	0.35	22,532	0.26	-2.8%
Nantucket	1,127	3.73	961	3.23	-2.3%
State	693,958	0.86%	782,320	0.87%