When Should Flu Trigger A School Shutdown?

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When Should Flu Trigger A School Shutdown?

ScienceDaily (Nov. 6, 2009) — As flu season approaches, parents around the

country are starting to face school closures. But how bad should an influenza

outbreak be for a school to shut down?

A study led by epidemiologists Brownstein, PhD, and Anne Gatewood Hoen, PhD

of the Children's Hospital Boston Informatics Program, in collaboration Asami

Sasaki of the University of Niigata Prefecture (Niigata, Japan), tapped a

detailed set of Japanese data to help guide decision making by schools and

government agencies. The analysis was published by the Centers for Disease

Control and Prevention in the November issue of Emerging Infectious Diseases.

" Currently many U.S. schools don't have specific or consistent algorithms for

deciding whether to shut down, " says Brownstein. " They don't always use

quantitative data, and it may be a political or fear-based decision rather than

a data-based one. "

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.

" You'd want get a school closed before an epidemic peaks, to prevent

transmission of the virus, but you also don't want to close a school

unnecessarily, " explains Brownstein. " We also wanted an algorithm that's not too

complex, that could be easily implemented by schools. "

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

The scenarios #2 and #3 performed similarly, with the greatest sensitivity and

specificity for predicting a flu outbreak (i.e., the fewest missed predictions

and the fewest " false positives. " ) Both gave better results than the single-day

scenario (#1). The researchers suggest that scenario #2 (with a sensitivity of

0.84 and a specificity of 0.77) might be the preferred early warning trigger,

balancing the need to prevent transmission with the need to minimize unnecessary

closures.

" Our method would give school administrators or government agencies a basis for

timely closure decisions, by allowing them to predict the escalation of an

outbreak using past absenteeism data, " says Hoen. " It could be used with data

from schools in other communities to provide predictions. It would leave

decision-making in the hands of local officials, but provide them with a

data-driven basis for making those decisions. "

Japan makes a good model for studying influenza in schools because it closely

monitors school absenteeism due to flu, requires testing for the flu virus in

students who become ill, and has a track record of instituting partial or

complete school closures during outbreaks. However, Brownstein cautions that the

scenarios might play out differently in the U.S. than they would in Japan,

mainly because students here aren't required to be tested for influenza as they

are in Japan, so it's less certain whether they actually have the flu. Also, the

vaccination status of students in this study was unknown.

Last spring, during the early days of the H1N1 influenza pandemic, the CDC

recommended first a 7-day school closure, then a 14-day closure after appearance

of the first suspected case. Later, as more became known about the extent of

community spread and disease severity, the CDC changed the recommendation to

advise against school closure unless absentee rates interfered with school

function. CDC's current guidelines

(http://www.cdc.gov/h1n1flu/schools/schoolguidance.htm, 10/21/09) don't provide

a specific algorithm, but state that " the decision to selectively dismiss a

school should be made locally, " in conjunction with local and state health

officials, " and should balance the risks of keeping the students in school with

the social disruption that school dismissal can cause. " When the decision is

made to dismiss students, CDC recommends doing so for 5 to 7 calendar days.

Researchers at the Harvard School of Public Health, the Boston University School

of Public Health, and Niigata University were coauthors on the study. The study

was funded by the Takemi Program, the Japan Foundation for the Promotion of

International Medical Research ation, the National Institute of Allergy

and Infectious Disease, the National Institutes of Health Research and the

Canadian Institutes of Health Research.

Journal reference:

1. Sasaki A, et al. Evidenced-based tool for triggering school closures

during influenza outbreaks. Emerging Infectious Diseases, November 2009

http://www.sciencedaily.com/releases/2009/11/091104152302.htm