Diane Barrera disinfects a classroom in Dallas, Texas, after the school was temporarily closed as a precaution in April after officials learned a student probably had swine flu. (Associated Press/LM Otero)

Closing schools to prevent the spread of swine flu in the fall should be avoided unless many students are sick and the virus starts to spread faster, according to U.S. guidelines released Friday.

"We know now that closing schools is not the best option in most cases," Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, told reporters.

Rather, officials should try to slow the spread of the H1N1 virus by keeping students further apart such as by moving desks, keeping classes from mixing and encouraging children to wash their hands several times a day with soap and water, especially after coughing or sneezing.

"Based on the experience and knowledge gained in jurisdictions that had large outbreaks in spring 2009, the potential benefits of pre-emptively dismissing students from school are often outweighed by negative consequences, including students being left home alone, health workers missing shifts when they must stay home with their children, students missing meals, and interruption of students’ education," the guidelines for students in kindergarten to Grade 12 read.

Schools for pregnant mothers and children with disabilities are an exception, given their high risk from flu.

School closure decisions rest with local school officials, but the CDC prepared the advice to help guide their decisions in dealing with the new flu strain for students in kindergarten to Grade 12, one-fifth of the country's population.

Close for high absenteeism

"Basically, this will be a tiered response," Education Secretary Arne Duncan said in an interview Friday on CBS's The Early Show. "If there's a handful of children at a school who might be sick, we want the parents to keep them home. If the numbers escalate dramatically, then we might have to close the schools."

Schools are considered a breeding ground for infections, and the CDC said schools should be vigilant about keeping sick students and staff at home. Every winter, seasonal flu outbreaks prompt a few schools to do so.

Specifically, the department also recommended:

• People with influenza-like illness stay at home until at least 24 hours after they are free of fever of 37.8 C or greater, or signs of fever, without the use of fever-reducing medications.
• Students and staff who appear to become sick with flu should be separated in a well-ventilated area and sent home.
• Respiratory etiquette, such as covering the nose and mouth with a tissue when coughing or sneezing and throwing the tissue in the garbage.
• Routine cleaning of all areas and items that are more likely to have frequent hand contact, such as keyboards or desks.
• Early treatment with antiviral medications for staff and parents of ill students at higher risk of complications from influenza.

"One change is the period of exclusion. It used to be seven days," Frieden said. "Now it is 24 hours after the fever goes away, and that's based on new information we have on how the virus spreads in the laboratory and person to person,"

If the severity of illness caused by the H1N1 virus worsens, then other strategies could be used, including:

• Actively screening for fever and respiratory infection symptoms when people arrive at school.
• Permitting high-risk students, staff and students with ill family members to stay home.
• Extending the exclusion period for people with influenza-like illness to at least seven days.
• Reviewing policies on school dismissals with public health officials if excessive absenteeism occurs or to reduce demand on the health-care system.

Last spring, some schools in Canada and the U.S. temporarily closed their doors.

With files from The Associated Press