When flu should trigger a school shutdown

BOSTON, Nov. 9 (UPI) -- Many education officials base decisions on when to close schools for flu on politics or fear rather than data, U.S. and Japanese researchers say.

Epidemiologists John Brownstein and Anne Gatewood Hoen of the Children's Hospital Boston Informatics Program in collaboration with Asami Sasaki of the University of Niigata Prefecture used a detailed set of Japanese data to help guide decision making by schools and government agencies.

Sasaki, Hoen and Brownstein analyzed flu absenteeism data from a Japanese school district with 54 elementary schools. Tracking four consecutive flu seasons -- 2004-2008 -- they asked what pattern of flu absenteeism was best for detecting a true school outbreak, balanced against the practical need to keep schools open if possible.

A school outbreak was defined as a daily flu absentee rate of more than 10 percent of students. After comparing more than two dozen possible scenarios for closing a school, the analysis suggested three optimal scenarios:

-- (1) A single-day influenza-related absentee rate of 5 percent.

-- (2) Absenteeism of 4 percent or more on two consecutive days.

-- (3) Absenteeism of 3 percent or more on three consecutive days.

Scenarios 2 and 3 performed similarly, with the greatest sensitivity and specificity for predicting a flu outbreak. Both gave better results than the single-day scenario (1), the study says.

The findings are published in the journal Emerging Infectious Diseases.