Dr. Michael Osterholm, chief epidemiologist at the Minnesota State Health Department, has compiled a list of 30 such investigations, often called "look-back studies," said Dr. Schwarz.

Dr. E. Russell Alexander, chief epidemiologist for the Federal program.

"We wanted to define what types of people are walking around with devices in them," said Roscoe Moore, chief epidemiologist at the Center for Devices and Radiological Health.

Dr. Rand Stoneburner, chief epidemiologist of the New York City Department of Health, said even these exceptions could have belonged to risk groups.

"These restrictions change social norms," says Michael Thun, chief epidemiologist for the American Cancer Society.

"There's no question that the ozone problem is really a problem that's not going to go away," said Dr. Clark Heath, chief epidemiologist for the American Cancer Society.

"From the evidence we have, it's a normal flu," said Dr. Lawrence Schonberger, chief epidemiologist in the viral activities branch.

He was appointed as chief epidemiologist shortly after the start of the project, when it was not progressing well.

She in turn alerted the City Board of Health, who immediately dispatched the chief epidemiologist.

Nigeria's chief epidemiologist Dr. Henry Akpan announced the discovery of the epidemic on 4 June 2010.