The Puerto Rican government has a list of 64 dead from Hurricane Maria, the tropical cyclone that hit the island in September 2017.。

This number, however, is "highly uncertain" notes the National Oceanic and Atmospheric Administration (NOAA). A new study published Tuesday in 
。 The New England Journal of Medicine 。puts that number at an estimated 4,645 — 70 times higher than the official estimate.。

"Our results indicate that the official death count of 64 is a substantial underestimate of the true burden of mortality after Hurricane Maria," write the authors, led by researchers from the Harvard T.H. Chan School of Public Health. 。

NOAA says that the storm, which caused some $90 billion in damage, is the third costliest in U.S. history. But it's the deadliest in over a century, since a hurricane pummeled Galveston, Texas, in 1900, killing more than 6,000 people. Back then, both NOAA and the National Hurricane Center didn't exist, so people were largely unaware of the power brought by the coming cyclone.。

Puerto Rico knew what was coming, but the hurricane's wind and downpours ravaged the island's water system and electrical grid. The storm blew down more than 80 percent of the island's utility poles and transmission lines. "Practically all cell phone service was lost and municipal water supplies were knocked out," said NOAA.。

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While some fatalities were caused by drownings and people being carried away in unprecedented floodwaters, the researchers show that thousands more succumbed during the period between September 20 through December 31, 2017. Around a third of those died due to "delayed or interrupted health care." 。

NOAA satellite GOES-16 captures an image of Hurricane Maria hitting Puerto Rico on September 20, 2017.Credit: cira/noaa 。

For this reason, the researchers relied upon a survey of 3,299 randomly chosen homes all over Puerto Rico, asking residents about the causes of death and other factors, like whether or not they were forced to leave their houses. Only 7 percent of households involved did not complete the survey.。

Once the surveys were reviewed, the researchers compared the rate of deaths that occurred between September 20 and December 31 in 2016 and 2017, finding that there were more than 4,500 "excess deaths" in 2017 — i.e., deaths that would not have occurred without the devastating impacts of Hurricane Maria. 。

"These numbers will serve as an important independent comparison to official statistics from death-registry data, which are currently being reevaluated, and underscore the inattention of the U.S. government to the frail infrastructure of Puerto Rico," write the authors.  。

If the official government report approximates this latest estimate by researchers outside the government, it may persuade current and future U.S. lawmakers to address the aftermath of a tropical cyclone more promptly, and with a heightened awareness of the necessary resources. 。