Many U.S. health-care workers who fell sick with swine flu likely didn't take precautions to protect themselves on the job, according to a report released Thursday.

About 80 American health-care workers have been confirmed with swine flu. The U.S. Centers for Disease Control and Prevention looked at 26 of these cases using detailed information as of May 13.

In half of these cases, health-care workers were infected at work, such as a clinic or hospital, and 12 caught the H1N1 swine flu virus from infected patients, CDC said in its weekly report on death and disease.

None of the doctors, nurses, technicians and other health care workers who fell ill fully followed CDC's infection control recommendations on isolating patients with swine flu and wearing masks, surgical gloves, eye protection and gloves when treating them.

The study's sample is too small to generalize about what is happening in clinics and hospitals, but it raises cautions for the pandemic, CDC said.

"I think we've been lucky that this first wave has not been of the lethality that some people feared," Dr. Michael Bell, a CDC official focused on infection control in health care settings, said at a news conference Thursday.

As of last Friday, the U.S. has 18,000 confirmed and probable cases of swine flu, including 1,600 who have been hospitalized and at least 44 deaths, according to CDC.

About 40 per cent of those hospitalized have been people with asthma, diabetes, heart disease and other medical conditions, said Dr. Daniel Jernigan of CDC's flu division in Atlanta.

Seasonal and pandemic strains

Jernigan said it's too soon to tell whether the new H1N1 virus is replacing seasonal flu viruses in the Southern Hemisphere, where flu season has started.

The pandemic virus predominates in countries with longstanding influenza surveillance programs, but testing is also showing human H1N1 and H3N2 viruses as well as some influenza B.

Health officials in Canada, the U.S. and other Northern Hemisphere countries are therefore buying seasonal flu vaccine as well as pandemic vaccine for the fall.

Elsewhere on Thursday, South Africa identified its first case of H1N1, the country's health department said.

As of Wednesday, the World Health Organization reported nearly 40,000 confirmed cases worldwide. Also as of Wednesday, the Public Health Agency of Canada reported 4,905 confirmed cases and 12 deaths.

With files from The Associated Press and The Canadian Press