UMass Amherst released weekly new case counts throughout the 2021-22 school year. The following is a comparison of the UMass new case counts to those from the MassDPH for Hampshire County. Most of the UMass cases are presumably also Hampshire County cases. The DPH uses declared county of residency; although the declared residency of the UMass cases is not publicly available, it seems likely that at least 3/4 of the UMass cases appear in the Hampshire County data. The Hampshire County population is 160,830 in the 2019 census, and the UMass population is 29,300 faculty, staff and students according to campus communication from the Public Health Promotion Center (Sept. 16, 2021). The UMass population that reports Hampshire County as their residence thus likely makes up about 20% of the county population.
To compare the case numbers from these partially overlapping populations, we can take the standard approach of relativizing the raw numbers to population size, as rates per 100,000 people. 100 new cases per week per 100K and above is considered “high” in the CDC transmission levels, and 200 per 100K is the bar used in their community levels along with hospitalization data. The above graph converts the raw weekly numbers (see the end of this post for those numbers and their source) to per capita rates using the populations from the last paragraph. The UMass rates in this graph range from a low of 34.1 per 100K for the week ending November 19th to a high of 1556.3 for February 15th.
New case rates are affected by testing, and because there was likely much more (asymptomatic) testing in the UMass population than in the general Hampshire County population, the actual relative disease prevalence was likely somewhat lower than these per capita rate comparisons would indicate. (Test positivity has the reverse bias: more testing tends to lead to a decreased percent positive.) It is therefore generally more informative to focus on changes in relative new case rates across time than to compare UMass to Hampshire County at a single point in time.
At some points, the UMass per capita rates were lower than Hampshire County – this was true from the week ending October 5 2021 through to the end of the first semester, with the exception of November 9th. (It was also true during the winter break, but the UMass population was of course much lower during this period, so these rates are artificially low). Since there was more testing at UMass, it is likely that there was in fact less disease prevalence there than in Hampshire County as a whole during the first semester after the first month. It is probably relevant that the UMass population had a much higher vaccination rate than the general Hampshire County population, that an indoor mask mandate was in place throughout the first semester, and that UMass was using wastewater surveillance testing with adaptive PCR testing.
The UMass per capita rates were also much higher at some points. This was the case at the beginning of both semesters. The first day of classes in the second semester was January 25. The UMass rate two weeks later was 1419.8 per 100K, compared to 477.5 for Hampshire County. The UMass rates approximated the Hampshire County ones in the middle of the semester, but were more than double on April 5th (348.1 vs. 121.9). The pattern of much higher UMass rates generally continued through to the end of the spring semester. It could well be relevant that the UMass Amherst indoor mask mandate was lifted March 9th.
It is not impossible that the changes in relative new case rates across time are due at least in part to changes in testing, but this seems especially unlikely to have played much of a role in the dramatic increase in the UMass cases relative to Hampshire County in the second part of the second semester. There appear to be no publicly available data that could be used to explore this possibility (see below).
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Data details
UMass data are from https://www.umass.edu/coronavirus/dashboard. They are currently unavailable at that site; the data for these graphs was copied from the presentations available during the 2021-22 school year. All of the data used for these graphs can be found in the Numbers file at this link; other formats available on request.
MassDPH data are from the downloadable dashboard data at https://www.mass.gov/info-details/covid-19-response-reporting. UMass cases seem to appear in the MassDPH data with a report date of about two days later, so the Hampshire County weeks in these graphs were chosen to end two days later, on the Thursday. The dates in the graphs are the Tuesdays.
The raw new case counts are shown below. The UMass data for April 28 (165 new cases) and May 3 (188) are the updated counts supplied the week after. They were originally given as 132 and 156 respectively. There were no UMass data released November 23 or December 28. The numbers from November 30 and January 4 were 77 and 360 respectively. They have been split over the two weeks.