Many health care workers fail to use required masks or respirators and often don’t think about the possible risks they’re causing, according to a new study.

The study by the Centers for Disease Control and Prevention (CDC) found that the inadequate use of mask or respirators put health care workers at risk of 2009 H1N1 infection which took place during the earliest stages of the 2009 pandemic in the U.S.

The study tracked 63 Southern California health care workers who had contact with six of the first eight laboratory-confirmed 2009 H1N1 cases in the U.S. H1N1 was the most common cause of flu that year.

Researchers found that 9 of 63 health care workers became infected with the 2009 H1N1 virus, which the authors say is likely from their contact with infected patients.

The researchers said that mask and respirator use was disappointingly low.

The authors said that only 19 percent reported using a mask during every patient encounter and that the use of a mask was especially low among outpatient workers, who also made up the majority of those who became infected with 2009 H1N1.

"The findings highlight the challenge of getting health care personnel to routinely wear Personal Protective Equipment," said Jenifer Jaeger, MD, MPH, an Associate Pediatrician at Massachusetts General Hospital.

"The study also suggests that greater attention to infection control and preparedness, particularly among outpatient workers, is needed."