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Volume 20, Number 7—July 2014

Dispatch

Rates of Influenza-like Illness and Winter School Breaks, Chile, 2004–2010

Gerardo ChowellComments to Author , Sherry Towers, Cécile Viboud, Rodrigo Fuentes, and Viviana Sotomayor
Author affiliations: Arizona State University, Tempe, Arizona, USA (G. Chowell, S. Towers); National Institutes of Health, Bethesda, Maryland, USA (G. Chowell, C. Viboud); Ministerio de Salud, Santiago, Chile (R. Fuentes, V. Sotomayor)

Main Article

Table 2

ILI incidence rate ratios for schoolchildren-to-adult age groups during 6-week periods surrounding school winter breaks, Chile, 2004–2010*

Age group, y ILI incidence rate ratio

p value
Before school break During school break After school break Before break vs. during break† During break vs. after break‡
Adults >20
Schoolchildren 5–14 2.59 (0.14) 1.28 (0.16) 1.98 (0.10) <0.001 <0.001
Schoolchildren 15–19 2.02 (0.07) 1.22 (0.04) 1.66 (0.07) <0.001 <0.001
Schoolchildren 5–19
2.40 (0.11)
1.26 (0.11)
1.87 (0.07)

<0.001
<0.001
Adults 20–64
Schoolchildren 5–14 2.52 (0.11) 1.25 (0.16) 2.00 (0.10) <0.001 <0.001
Schoolchildren 15–19 1.97 (0.05) 1.18 (0.04) 1.68 (0.07) <0.001 <0.001
Schoolchildren 5–19
2.33 (0.08)
1.23 (0.11)
1.89 (0.08)

<0.001
<0.001
Adults >65
Schoolchildren 5–14 3.82 (0.62) 1.61 (0.23) 1.85 (0.14) <0.001 0.187
Schoolchildren 15–19 2.94 (0.46) 1.52 (0.08) 1.56 (0.11) 0.001 0.401
Schoolchildren 5–19 3.52 (0.56) 1.58 (0.16) 1.75 (0.12) <0.001 0.206

*The “after break” period begins 2 weeks after the winter break ends because the reduction in the incidence rate ratio during the winter break was maintained on average for 2 weeks after the end of the winter break. ILI, influenza-like illness.
†p value of a 1-sided Z test comparing the average incidence rate ratio (ratio of incidence rate for schoolchildren to incidence rate for adults) during the 2-week period before the school break to that during the winter break. Small p values indicate that the incidence rate ratio for the period before the break is significantly higher than that for the period during the break; p values near 1.00 indicate that the incidence rate ratio for the period before the break is significantly lower than that for during the break.
‡p value of a 1-sided Z test comparing the average incidence rate ratio during the 2-week period after the school break to that during the winter break period. Small p values indicate that the incidence rate ratio for the period after the winter break period is significantly higher than that for the period during the winter break; p values near 1.00 indicate that the incidence rate ratio for the period after the break is significantly lower than that for the period during the break.

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