May 29 (UPI) -- A Harvard study released Tuesday determined at least 4,645 people in Puerto Rico died as a result of Hurricane Maria, a sharp contrast to the official death toll of 64.
The study, conducted by researchers from Harvard T.H. Chan School of Public Health and published in the New England Journal of Medicine, blamed most of the deaths on delayed medical care.
When the hurricane hit Puerto Rico in September, it essentially wiped out the entire electrical grid and much of the island territory's infrastructure, including roads, hospitals, water supply and telecommunications networks. The National Hurricane Center said Hurricane Maria caused an estimated $90 billion damage in Puerto Rico and the U.S. Virgin Islands, the third-costliest hurricane in U.S. history.
Researchers said they surveyed 3,299 randomly selected households in Puerto Rico to assess deaths after the hurricane -- including those not considered to be related to the storm. They compared the number of deaths after the hurricane to the same time period in 2016.
There were 14.3 deaths per 1,000 people from Sept. 20 through Dec. 31, resulting in 4,645 more deaths in the same time period the year before -- a 62 percent increase in mortality rate.
"The mortality rate remained high through the end of December 2017, and one third of the deaths were attributed to delayed or interrupted healthcare," the study said.
Researchers said the disparity between the official death toll and their estimates likely resulted from difficulties in physically verifying the causes of death. The Institute of Forensic Sciences must confirm all disaster-related deaths in Puerto Rico.
"This requires that bodies be brought to San Juan or that a medical examiner travel to the local municipality to verify the death, often delaying the issuance of death certificates," the study says. "Furthermore, although direct causes of death are easier to assign by medical examiners, indirect deaths resulting from worsening of chronic conditions or from delayed medical treatments may not be captured on death certificates."
The Puerto Rican government has launched an external review of its death-registry data as a result of the difficulties.
"It took too long to understand the need for an appropriate response was not about politics but about saving lives," tweeted San Juan Mayor Carmen Yulin Cruz, who was vocal in her criticisms of the federal government's handling of relief efforts after the hurricane.