Several counties across Alabama have seen a marked increase in coronavirus cases over the last week, after maintaining relatively low numbers through the early stages of the pandemic.

As of April 1, 45 of Alabama’s 67 counties had fewer than 10 confirmed cases of the virus, according to data from the Alabama Department of Public Health. Many of those counties are now seeing rapid increases in case counts.

Marshall County, in northeast Alabama, had just six cases on April 1. It now has 258, and over the past seven days has seen the fastest rate of new cases in the state. It’s seven-day case growth rate was 85.6 percent on Friday afternoon.

Ten counties saw a 50 percent or higher increase in cases from April 18 to April 24. Escambia County, along the Florida border, was second behind Marshall with a 75 percent increase in official cases over the last week.

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Pike County, home of Troy University, was third, with a 67.7 percent increase from 34 cases to 57. Pike is one of several counties in and around the Wiregrass region in southeast Alabama to see large percentage increases in case counts. That region was slow to start seeing confirmed cases.

Other pockets with high percentage increases include parts of west Alabama in the Black Belt, some of the counties around Marshall in northeast Alabama and a pocket in the northeast part of the state.

For some rural counties, or counties that were late to start testing, a large percentage increase may involve just a small number of actual positive cases. For example, while Escambia climbed 75 percent in a week, it only rose from 12 cases to 21.

But that’s not the case in Marshall County.

Marshall’s rapid increase in cases is one of the more shocking in the state. Along with being the highest percentage increase, it’s also the second highest in terms of raw cases added. It added 119 cases in just seven days. That trails only Mobile County, which added 172 cases over that time.

Jefferson County, the most populous in the state, added 105. It was the only other county with more than 100 new cases over that time span.

Tallapoosa County, which was rapidly gaining cases earlier this month, added another 74 cases this week, the fourth highest raw total. Those new cases represent a 41.1 percent increase. It had 254 cases Friday afternoon, four less than Marshall.

Chambers County, which early on was one of the hardest hit counties in the state, may now be on the other side of the curve, but it’s not out of the woods yet. It added 35 cases in seven days, for an increase of 14.7 percent, well down from its pace earlier this month.

Because of the way ADPH compiles its numbers, some counties actually see their case counts go down. That happened this week in Conecuh County, which had one fewer case on the books on Friday than it did last week.

Of course, the number of cases will rise as testing increases. More testing doesn’t entirely explain the results in every county. But testing began unevenly across the state last month, and many counties saw a rapid rise over the last few weeks. No county saw a greater increase in testing than Tallapoosa, which since April 7 saw a more than 1600 percent increase in tests performed by state labs.

The only other three counties with testing increases over 500 percent were neighbors of Tallapoosa - Chambers, Lee and Macon.

AL.com reader Bill Beck, a retired engineer, helped compile data for this report.

Do you have an idea for a data story about Alabama? Email Ramsey Archibald at rarchibald@al.com, and follow him on Twitter @RamseyArchibald. Read more Alabama data stories here.