As the number of cases of lung disease injuries and deaths associated with the use of e-cigarettes continue to rise around the country, many are looking for warning signs that the products were dangerous early on.

According to Bloomberg, there were, and scientists, regulators and proponents of the products missed, ignored or even downplayed the risks, which were apparent in medical literature, government documents and interviews with doctors.

The number of lung injury cases associated with vaping jumped to 530 this week, and eight deaths have been reported in the U.S. The string of illnesses has led the CDC and several states to investigate the root cause, and a criminal probe has also been opened. Amid the turmoil, the CEO of one of the biggest e-cigarette makers, Juul, stepped down this week.

However, vaping injuries in the U.S. have been reported since as early as 2011, Bloomberg found. Scientists and researchers may have been more focused on whether vaping helped adults quit smoking, Bloomberg noted. Other cases may have also been overlooked.

“These cases have been reported for several years but nobody put two and two together because they were too isolated,” Stanton Glantz, a tobacco researcher from the Center for Tobacco Control Research and Education at the UC San Francisco, told Bloomberg.

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