Dependence between observed weekly number of CDI – AR1-model.

<p>A and B: autocorrelation function (ACF) of normalized residuals of the AR1-model fitted to data of all hospitals (<b>A</b>) and of teaching hospitals only (<b>B</b>) including a fitted cubic representation of the CDI trend over time and seasonality. As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099860#pone-0099860-g002" target="_blank">figure 2</a>, the blue lines correspond to the threshold for significance of correlation (dependence) (p<0.05) between lagged weekly observations up to week 20. Crossing of this threshold by the AR1-model residuals at lag 2 suggests the AR1 structure (symptomatic cases primarily cause acquisition of <i>C. difficile</i> among patients admitted to hospital up to one week later and, to a lesser extent, to cases admitted beyond this time), does not fully explain the dependence structure between weekly observations.