susan bigelow / ctnewsjunkie
susan bigelow / ctnewsjunkie

Prevalence maps, which show the number of cases per 10,000 people, are useful for determining how severe an outbreak is in a given area over a specific period of time. They also factor in differences between population density per town – Hartford is naturally going to have more cases than East Windsor, because there are more people there. That’s why they examine cases per 10,000 people, rather than just cases per town.

This week, we’ve developed a prevalence map for the week ending April 12, and another for the week ending April 19. Both calculate the rate of infection per 10,000 people. Mouse over the current interactive version of the map to get specific data for each town.

We were originally using a map that showed the rate of infection per 10,000 for the entire crisis stretching back into March. This was becoming less useful, as it was growing harder to see where the pandemic was receding and where it was growing more severe.

Prevalence maps are supposed to be snapshots in time, and the old prevalence map was showing the disease over a longer and longer period of time. That would have eventually created a map that was functionally identical to the current cases per town map – with a slight correction for population. Another problem was that towns that previously had bad outbreaks but were now seeing fewer cases, such as Westport, weren’t represented. Towns that had seen relatively few cases initially but were now seeing many more, such as Woodbridge, were not adequately represented either.

And here is the current interactive map based on data through April 19:

The new weekly maps should give readers a better understanding of the current state of the epidemic in Connecticut. This will be especially important as our leaders weigh difficult decisions about when to begin re-opening the state’s economy.

The differences between the map for the week ending April 12 and the map for the week ending April 19 shows the concentration of new COVID-19 cases moving out of Fairfield County, to what has to be great relief.

The two areas with the highest percentage of new cases per population are the Hartford area and the New Haven area. The New Haven area is likely hitting its peak, while Hartford may be doing so this coming week. New Haven will be less hard hit than Fairfield County was, and hopefully Hartford will be somewhat less severe than either of them. Rural counties have by and large escaped major spikes in cases so far, and this will likely continue to be true unless something changes.

A few caveats: this map relies on testing data, and tests are not always given to everyone who may have the disease. Address verification may take several days, and test results are still lagging several days behind as well.

By and large, though, this past week saw a plateauing or even a slowing in the rate of growth of the virus in many areas. That is a very good thing, and suggests that social distancing measures are working.

We’ll update this map next Sunday to see how things stand at that point.

Susan Bigelow is an award-winning columnist and the founder of CTLocalPolitics. She lives in Enfield with her wife and their cats.

DISCLAIMER: The views, opinions, positions, or strategies expressed by the author are theirs alone, and do not necessarily reflect the views, opinions, or positions of

Susan Bigelow

Susan Bigelow is an award-winning columnist and the founder of CTLocalPolitics. She lives in Enfield with her wife and their cats.