The study is a follow-up survey of 71,000 people, all who were possibly exposed to pollutants on Sept. 11, 2001, the New York Post reported.
The survey is being conducted to determine if respondents who previously reported being ill are still so, and if those who indicated being healthy are now sick.
New York City Health Commissioner Thomas Frieden said the study has been a planned procedure and is not a response to any recent rash of health crises, as was thought by some emergency responders.
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