Figure legends
Figure 1. Weekly reported virologically-confirmed influenza cases, and all-cause and influenza-like-illness (ILI) specific absences in Allegheny County, Pennsylvania, USA, during influenza seasons from 2007 to 2015 . Surveillance of influenza cases during each influenza season in Allegheny County occurred from the 40th week of one year to the 20th week of the following year (solid black lines). All-cause absences were collected for the entire school year for each school district, and data were restricted to their respective influenza seasons. Nine school districts within Allegheny contributed to weekly counts of all-cause absences. Additionally, all-cause and ILI-specific absences were collected during independent influenza seasons for three separate studies: 2007-2008 (PIPP study), 2012-2013 (SMART study), and 2015-2016 (SMART2 study). Absence surveillance data were not collected during the 2008-2009 or 2009-2010 influenza seasons. White space on the x-axis reflects periods when data were not collected for this analysis, whereas black lines on the x-axis (in negative y values) indicate time periods when data is available. The Allegheny County student population averaged 43,636 students across the nine school districts, comprising 122 schools (57 elementary, 20 middle, and 18 high schools, and 24 charter/independent schools). County-level data for 2010-2011 season were not available for 3 school districts.
Figure 2. Four model predictions of confirmed influenza in Allegheny County using leave one season out validations for the 2010 to 2014 influenza seasons. Model predictions of four negative binomial models (calendar week, average weekly temperature, average weekly relative humidity (red), one-week lagged county-level all-cause absences, temperature, and week model (yellow), one-week lagged county-level all-cause absences, relative humidity, and week model (blue), and one-week lagged county-level all-cause absences, temperature, relative humidity, and week model (purple)) using leave-one-season-out validation approaches showing model predictions compared to observed virologically-confirmed influenza cases (black line) in Allegheny County, Pennsylvania, USA, A) weekly counts during each of the 2010-2011 to 2014-2015 influenza seasons, B) the change in predicted cases using modeling including absences compared to a seasonal model excluding absences (red), and C) the cumulative proportions of predicted and observed influenza cases for each season. R2 was obtained using a linear regression, where the observed cases from the left-out season are the dependent variable and the independent variable were predicted cases from a negative binomial model of week-lagged county-level all-cause absences, relative humidity, temperature, and calendar week.
Figure 3. Mean and relative absolute errors for predictions using grade-specific absence models to predict influenza in Allegheny County Pennsylvania from 2010 to 2014 influenza seasons. Mean absolute errors were estimated from univariate grade-specific weekly absences models (A), and the relative mean absolute error compared models of grade-specific weekly absences, week of the year, average weekly relative humidity, average weekly temperature to models of calendar week, average weekly relative humidity, and average weekly temperature (B). Colors reflect the three different school types: red is elementary school, green is middle school, and blue is high school. Solid black line refers to a relMAE of 1, where mean absolute errors of the grade-specific absence models and models excluding absences are the same.