Of the 12 health care personnel who were infected by patients, 11 reported information on their use of personal protective equipment when caring for the presumed source patient.
Three reported always using either a surgical mask or an N95 respirator.
Five reported always using gloves.
None reported always using eye protection.
None reported always using gloves, gown and either surgical mask or N95 respirator.
One physician reported always using an N95 respirator when with an infected patient, but also reported never having had a fit test for the respirator. There was no information on whether the doctor wore a gown or eye protection.
A nurse anesthetist reported always using gloves and a surgical mask with the presumed source patient, but only sometimes using a gown, N95 respirator and eye protection.
And one registered nurse who was caring for an H1N1 patient reported always using a surgical mask and gloves with the patient but never using a gown, N95 respirator, or eye protection.
The CDC infection-control recommendations for the care of H1N1 patients included the use of fit-tested N95 respirators, eye protection, and contact precautions, in addition to routine infection-control practices used for seasonal flu.
Among the 11 health care workers for whom data is available, "none adhered to these recommended practices completely," the agency said.
On the positive side, the agency said, among confirmed and probable cases reported to CDC as of May 13 in adults ages 18 through 64, about 4 percent have occurred in health care workers.
About 9 percent of working adults in the U.S. are employed in health-care settings, the agency said.
The comparison should be interpreted with caution, the CDC said, because the case reports are geographically uneven and substantial under-reporting is probable.
Whatever the actual risk, the CDC noted, it is mostly found in outpatient settings.
As of May 31, only 6 percent of 10,053 H1N1 patients needed inpatient care, the agency said. And six of the 12 health care workers whose infections were associated with employment said they had been caring for outpatients in the week before the onset of symptoms.