Results of the logistic regression for the case-case studies.

(A) Odds ratios and their associated P-value for all the selected cases in the univariate models. *Factors with P<0.05 are considered as significant. †Factors with a P<0.25 are entered in the multivariate model. (B) Odds ratios and P-values for the final multivariate models. Previous steps, consisting in removing one by one the factors with the highest P-value at each step, are not shown. The program used to execute the analysis gave P = 0.002 for the overall model fit comparing 2002–06 with 1997–01 and P = <0.0001 comparing 2007–10 with 1997–01. aHumans are grouped into four age groups with the reference group being young children (0–4 years) (see Table S2) and the odds ratio indicates the relative amount by which the odds of the outcome changes when the value of the predictor value is increased by 1.0 unit. bReference group.