The aftereffects of 2017's Hurricane Irma appear to have killed more than 400 senior residents of Florida nursing homes, a new university study shows.

Researchers at the University of South Florida and Brown University concluded that 433 additional patients died within 90 days of the September 2017 storm, compared to the same period in 2015, when there were no hurricanes.

Their study examined health data for 62,000 patients at 640 Florida nursing homes obtained from the Centers for Medicare and Medicaid Services, according to the Tampa Bay Times. The study was recently released.

The study was prompted by the of 12 residents at a Broward County nursing home. Authorities said those deaths were caused when the storm disabled the central air conditioning and the staff failed to move patients to a nearby hospital. An administrator and three nurses who worked at the Rehabilitation Center at Hollywood Hills have been charged with failing to prevent the deaths.

The researchers found that long-term nursing home residents suffered not only increased after Irma, but more hospitalizations.

"Nursing homes need to really pay attention to these people when they're in the process of reacting to a hurricane," said co-author Lindsay Peterson, a research assistant professor of aging studies at USF.

Brian Lee, director of Families for Better Care, a nonprofit that advocates for better services at , said the study shows that nursing homes need to do a better job preparing for hurricanes.

"This is an extremely vulnerable population, and nursing homes and other facilities need to do a better job of hardening their facilities to protect our loved ones," Lee said.

After Irma, the Florida required nursing homes and assisted-living facilities to install generators to keep residents cool in case of a storm. But the laws need to be tougher, Lee said.

Nursing homes need generators that can allow cooling of residents in their rooms, not spot coolers that were used at Hollywood Hills. That required moving residents into large spaces to keep them cool. Fewer than 100 of the state's long-term care facilities had temporary generators during Irma, the Times reported.

"We need to make sure that facilities can withstand these storms and not worry about transferring residents around and exposing them to potential transfer trauma," Lee said.