Statistical analysis The analysis of the data will be mostly descriptive. The incidence of resistance will be computed as a percentage, the denominator being the number of episodes of Gram-negative bacteremia, and the numerator being the number of episodes classified as "resistant". The relationship between Resistance and prognostic factors / characteristics will be investigated mostly in univariate analysis, applying standard summary measures (tables, quantiles) and non-parametric tests (chi-squared or Fisher Exact, Mann-Whitney or Kruskal-Wallis) - for categorical and continuous variables respectively. Possibly, a multivariate analysis could also be applied, using logistic regression; random effects models or GEE could be used to account for dependence of observations - nested by patient and center. The short-term mortality (at 7 and 30 days) will be computed as a percentage - unless a relevant proportion of loss to follow-up will be observed.