Elijah Alfred "NatureBoy" Alexander, Jr. keeps cool under a tree in Lafayette Park in Washington, D.C. on July 22. (Marvin Joseph/THE WASHINGTON POST)

The unusually high number was due in part to the long stretch of hot weather. Temperatures had topped 90 degrees for nine days before the week began, reaching 106 degrees July 22 at Baltimore-Washington International Thurgood Marshall Airport and 101 degrees July 29.

"The cumulative effect of day after day of this sort of heat takes a toll, particularly on people who have weakened circulatory systems," said Fran Phillips, deputy secretary for public health at the Maryland Department of Health and Mental Hygiene. "The effect is worse when there are no breaks in the hot weather. People with circulatory problems have an extra load on their heart and lungs."

A review of last year's heat-related deaths found that most involved people "who do not have air conditioning at home and who do not leave home," Phillips said.

All of the people who died in last week's heat had underlying health conditions that made them more vulnerable, she said.

Read the full story at baltimoresun.com.