Raleigh, N.C. — State public health officials notified the health departments in New Hanover County on Thursday that four elementary school-aged children in the two counties have contracted the swine flu.

Local officials immediately notified the parents of the children, and the county health department began working to determine who might have been exposed to the H1N1 virus before the children showed symptoms. People who have been in close contact with the children will be advised to go home to limit the spread of the illness.

Three of the students attend Gregory Elementary School of Science, Mathematics and Technology, while the fourth attends Snipes Academy of Art and Design. Officials said they aren't recommending any school closures.

The four new cases bring the total of confirmed swine flu cases in North Carolina to 20. Cases in Onslow and Brunswick counties were confirmed earlier this week.

Meanwhile, public health officials said Orange County's first confirmed case of swine flu appears to have been contained to a UNC Healthcare worker.

The unidentified person, who works at University Pediatrics in Durham, tested positive for the H1N1 virus last Friday, and was immediately isolated to contain the spread of the illness.

Ten co-workers received preventive treatment, and none has exhibited flu-like symptoms, said Dr. David Weber, an epidemiologist and associate director of the UNC School of Medicine. Seventeen patients who came in contact with the worker also were offered anti-viral medications, but not all took them, Weber said.

Some of the clinic patients have been tested for swine flu, but all tests have come back negative, Weber said.

The incubation period for H1N1 is typically one to four days, although it could appear as late as seven days after contact. Weber said officials believe that there won't be more related cases of swine flu in Orange County.

The employee also expects to return to work shortly after recovering from the virus, he said.

More than 7,900 cases of H1N1 have shown up in 48 states, and 11 people in the U.S. have died from the disease, according to the U.S. Centers for Disease Control and Prevention.

At least 42 countries have confirmed cases of the disease, which has sickened more than 11,000 people and caused about 90 deaths, the World Health Organization reports.