Massachusetts Reporting Change: Probable Cases

On September 2, Massachusetts once again changed its coronavirus reporting – this time changing the definition of “probable cases”. According to the Massachusetts Dashboard “The previous case definition defined probable cases as individuals: with a positive antigen or serology test AND symptoms or likely exposure; with COVID-19 listed as an underlying or contributing cause of death on a death certificate; and with appropriate symptoms and likely exposure.”

However, “The new case definition updates the clinical criteria associated with COVID-19; defines probable cases as individuals: with a positive antigen test, with COVID-19 listed as an underlying or contributing cause of death on a death certificate, or with appropriate symptoms and likely exposure .” Furthermore, “the criteria indicating likely exposure are now restricted to known contact with a case or association with a specific outbreak. Individuals with positive serology (antibody) tests have been placed in a new suspect category which is not reportable to CDC.”

The Commonwealth indicates that the new reporting standard is more objective, is able to be more consistently applied through time, and brings Massachusetts’ reporting of probable cases more in line with the reporting standards of other jurisdictions. (Note that not all jurisdictions even report probable cases).

Significantly, all of the prior reporting on probable cases, hospitalizations, and deaths has been adjusted and backdated for this change. What are the ramifications of this? First, the Commonwealth reduced the number of probable cases substantially – from 9,755 under the old standard to 1,705 under the new standard (a reduction of 8,050).

The chart below shows the weekly change in probable cases over time. Most of the cases dropped were from May, when the pandemic was raging in Massachusetts. However, a substantial number of cases from June through August were also eliminated.

The number of probable deaths from Covid19 also dropped, but much less substantially – from 233 to 207 (26 deaths). The eliminated probable deaths are spread relatively uniformly over time. Ironically, however, the first death reported in Massachusetts, which occurred on March 10, was a probable case that was eliminated. I have adjusted my reporting statistics where possible to reflect these changes in cases and deaths.

The other consequence of this change is that it impacts how Massachusetts stands relative to other states in the case horse race (a horse race nobody wants to win). Early on, Massachusetts was third in the country in the number of cases, trailing only New York and New Jersey. As our case rates dropped substantially, and the pandemic spread to the Sun Belt, we had dropped in the rankings to 13th in the total number of cases, and 17th in cases per capita (per the worldometers aggregation site We are now ranked 16th in total cases and 22nd in cases per capita.

Unfortunately, our per capita death ranking remains unchanged – we have the 3rd highest per capita death rate, trailing (once again) only New York and New Jersey.

4 replies on “Massachusetts Reporting Change: Probable Cases”

Thank you for this blog! It is such a public service for you to interpret and post information for us in an easily digestible, elegant way. We are grateful.

Thanks once again for these updates. While I don’t want you to feel obligated, I’m hoping you have more readers so these updates keep coming. ?

Thanks. I intend to. In terms of getting more subscribers, I’ve only hawked this on the Globe comment section, so we’ll see how it goes.

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