LOS ANGELES, Jan. 2 (Xinhua) -- Short-duration school closures during a flu pandemic may increase infection rates and prolong an epidemic, according to a new study.

    The findings indicate that schools may need to be closed for at least eight weeks in order to significantly decrease the spread of infection.

    University of Pittsburgh researchers followed an agent-based computer simulation model of Allegheny County, Pennsylvania, which represented the county's population, school systems, workplaces, households and communities.

    Simulations were based on the movement of residents each weekday from their households to designated workplaces or schools, and included 1.2 million people, 200,000 of whom were school-aged children.

    The study also included more than 500,000 households and nearly300 schools.

    The study found that closing schools for less than two weeks can increase transmission rates by returning susceptible students back to school in the middle of an epidemic when they are most vulnerable to infection.

    "Although closing schools may seem like a reasonable way to slow the spread of flu, we found that it was not effective unless sustained for at least eight weeks after implementation," said study lead author, Bruce Lee, assistant professor or medicine, epidemiology and biomedical informatics.

    Closing schools quickly at the start of an outbreak was much less important than keeping them closed continually throughout the epidemic, he added.

    The value of school closures has been debated as a possible strategy to stem or slow the current H1N1 influenza pandemic.

    The study also found that identifying sick students individually and keeping them from attending school had minimal impact on an epidemic. In addition, there were no significant differences between individual school closures and system-wide closures in mitigating an epidemic.

    The findings were published on the Jan. issue of the Journal of Public Health Management and Practice.