HOUSTON -- Harris County health officials warned residents to take precautions to protect them from the swine flu, even though no cases have been reported in the Houston area, KPRC Local 2 reported Monday.

Health officials said it's just a matter of time before someone contracts swine flu in Houston because of the city's large population and the amount of travelers.

"It is certainly reasonable to expect that we will be seeing it shortly. It is here in Texas. It's in five states. It's in several countries. One would expect that we'd see it in an area as large a metropolitan and with as much domestic and international traffic," said Dr. Herminia Palacio with Harris County Public Health and Environmental Services.

Health officials said people can reduce the risk of catching the illness by keeping a good distance from others, washing hands frequently and staying home when sick.

"I think the most important thing right now is if you are sick, don't go to work," said Kathy Barton of the Houston Health Department. "If your children are sick, don't send them to school."

The Houston Independent School District sent out automated messages and e-mails to warn parents about the danger. School nurses are monitoring students for symptoms. If students have temperatures of 100 degrees or more, they will be sent home and urged to see a doctor.

Concerns about swine flu has people clearing drugstore shelves of masks and antibacterial products. Stores have sold out of masks.

Palacio said, however, that face masks and respirators are really only helpful in areas of confirmed cases. They are not recommended in Houston yet.

Anyone who shows flu-like symptoms of fever, lethargy, nausea, vomiting or diarrhea is urged to see a doctor.

Barton said the only way to know if someone has swine flu, or any other flu, is to have a doctor do a nasal swab test.

Harris County set up a phone bank to answer residents' questions about the swine flu. Call 713-212-0200 from 8 a.m. until 8 p.m. Monday through Friday.

U.S. Outbreak 'Less Severe' Than Mexico

Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, said that so far the disease in the United States seems less severe than the outbreak in Mexico, where more than 1,600 cases have been reported and where the suspected death toll has climbed to 149. No deaths have been reported in the U.S, and only one hospitalization.

"I wouldn't be overly reassured by that," Besser told reporters at CDC's headquarters in Atlanta. He raised the possibility of more severe cases -- and deaths -- in the United States.

"We are taking it seriously and acting aggressively. ... Until the outbreak has progressed, you really don't know what it's going to do," Besser said.

Warning Issued For Mexico Travel

The head of the Homeland Security Department said travel warnings to Mexico will remain in place as long as swine flu is detected.

Secretary Janet Napolitano made the announcement at a news conference Monday. She said the Centers for Disease Control had issued an alert and the State Department's version would be forthcoming.

The virus began in Mexico and had spread to the United States and beyond, with at least 40 cases reported in the U.S.

Napolitano said she had been in touch with Mexican officials and border state leaders to coordinate responses to the outbreak.

Many travelers arriving in Houston from Mexico have been wearing masks because of swine flu fears.

"Everyone was covering their mouth and people were talking about suspending school and church services," said Nancy Guzman, who arrived by bus from Monterrey, Mexico.

Travelers from Mexico City said they saw the same thing.

"The roads are empty and all the public places are basically empty," Enrico Gianetti said. "Everybody knows to stay home."

Houstonian Patricia Casanova brought her grandchildren who live in Mexico City to Houston as a precaution.

"Schools have been let out, football games have been suspended," she said. "They're taking a lot of steps and very cautious."

Mexico's consul general in Houston said people should be aware of what's happening, but not panic.

"For people who get sick, there's enough medication to be treated," Consul General Carlos Gonzalez said.