Part of our Losing to Lyme series

Lyme disease is a big — and growing — problem in Massachusetts. Here's how the number of cases has risen over the last 12 years:

A few important notes on the data:

In 2012, the state started counting confirmed and probable cases of Lyme disease, which is why there's a clear jump that year.

Data is compiled based on "passive surveillance," which means the state counts reports of positive tests from laboratories, and also waits on health providers to report probable Lyme disease cases.

Other factors can affect Lyme cases, such as the drought conditions from spring 2015 to the spring of this year, because that can affect the numbers of ticks.

The CDC estimates that just 10 percent of cases of Lyme disease are actually reported, so the actual prevalence of disease is much higher.

Below is a county-by-county look at those cases. The map has three views: