(with data to June 13, 2020)
Trends in new COVID-19 cases will be important for state and local decisions about when and how to reopen schools. Here we look trends for the largest eastern Massachusetts counties using case counts come from Massachusetts Department of Public Health (DPH) and county population figures come from the UMass Donahue Institute. Keep in mind that counts reflect not only the incidence of the disease but also the amount of testing that is done.
Chart 1 shows cumulative COVID-19 cases counts per 1000 population. These are cases as reported by DPH and consist of only confirmed cases to May 31, 2020 but include both confirmed and probable cases from June 1, 2020 forward. Essex County and the other non-Boston areas are on lower paths of cumulative case counts than Suffolk County. Essex County confirmed case counts per capita are now consistently well above the statewide average after tracking very near the state average up to April 2nd. Essex County cumulative cases per capita are now 29 percent above the state average, and 37 percent above neighboring Middlesex County.
Chart 2 presents daily new cases as a seven-day moving average. This smooths out the day-to-day variation and avoids any day-of-the-week reporting effects. From mid-April to mid-May Essex County daily COVID-19 cases per capita tracked above other eastern Massachusetts Counties excepting Suffolk County and was higher than Suffolk County at times in May. Recently the most populous eastern Massachusetts counties have had fairly similar rates for new COVID-19 cases. These rate have been trending generally downward in May and for the first part of June.
Notes on reported case count methods and data: (1) The change in reporting of probable cases added to case counts on June 1 and increase the seven day moving average significantly for counts on June 1 to June 7; (2) The Massachusetts Department of Public Health (DPH) on April 24th noted a reporting error that reduced case counts for data from April 13 to April 23 due to a backlog in reporting cases from Quest Diagnostics. DPH provided revised case counts for that period for Massachusetts, but not for individual counties. The results reported here thus reflect under-reporting of COVID case counts for April 13 to 22 and increased case counts for April 24 to account for the previous under-counts