In a surprise twist, authors here retracted findings of a study that found N95 respirators were better than surgical masks at preventing flu.

After a re-analysis prompted by questions from reviewers, the findings were no longer significant, said Holly Seale of the University of New South Wales in Sydney, Australia.

The original study, presented earlier this year, formed the basis of several important policy decisions, including Centers for Disease Control and Prevention guidance on the use of masks in a health care setting.

The retraction — near the end of a presentation at the annual meeting of the Infectious Diseases Society of America — prompted a “rush to the microphones” by those involved in flu prevention, one expert said.

The findings appeared to differ — not only from previous reports, but also from the abstract submitted to this meeting, said Dr. Andrew Pavia of the University of Utah.

Seale acknowledged those differences and agreed that the original results no longer stand. She was not immediately available for additional comment.

The lead author of the study, Raina MacIntyre, also of the University of New South Wales, did not attend the meeting here.

The retraction took experts here by surprise, although many had been critical of some statistical aspects of the study, according to Dr. Neil Fishman of the University of Pennsylvania.

“I think there was little bit of shock that there was such a large change (in the results),” he told MedPage Today after the session.

The study was first presented in San Francisco earlier this year and led to important policy decisions in the United States.

Among other things, it influenced an Institute of Medicine recommendation that health care workers caring for flu patients should use the more expensive N95 respirators.