Puerto Rico's official death toll for deaths as a direct result of Hurricane Maria is 64, according to the Associated Press.
Researchers from Harvard University who led the new study said 64 deaths are a "substantial underestimate."
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The researchers found that, on average, households went 84 days without electricity, 68 days without water and 41 days without cell phone coverage after the hurricane hit on September 20, 2017, until December 31, 2017.
A total of 31 percent of those surveyed reported a disruption in their medical care and 14 percent said they were unable to access medication after the hurricane struck.
"Indirect deaths resulting from worsening of chronic conditions or from delayed medical treatments may not be captured on death certificates," researchers said.
Many survey respondents were still without water and electricity at the time of the study's publication.
This is the latest study to determine how many people died during or after the Category 4 storm.
"The difference is that we went out and we had boots on the ground and we did the interviews," Domingo Marques, an associate professor of clinical psychology at Carlos Albizu University in Puerto Rico, told CNN. "Statistically, it's like having interviewed the whole island."
The storm caused an estimated $100 billion in damage to the U.S. territory and resulted in the largest blackout in U.S. history. The entire island of 3.3 million people was without power, including hospitals and nursing homes, where people depended on respirators and other medical equipment.
Experts told CNN it is difficult to define which deaths were "caused" by the hurricane during the chaotic and unsafe conditions.
Puerto Rico has hired George Washington University to conduct an assessment of Maria's death toll. Those results have not been released ahead of the 2018 hurricane season.
At least one independent researcher is calling the methods of this new study into question.
"This estimate could be off by thousands. Easily," Donald Berry, a professor of biostatistics at the University of Texas MD Anderson Cancer Center, told The Associated Press.
The government of Puerto Rico issued a statement on Tuesday, saying it welcomed this new research and would analyze it, CBS reports.