Fig. 3.

Lower respiratory tract microbial diversity is associated with illness severity in critically ill patients. Correlation analysis using Spearman’s rank correlation coefficient demonstrated an inverse association between APACHE II score and Shannon diversity (r = − 0.46, p = 0.013; a), Simpson diversity (r = − 0.44, p = 0.017; b) and Observed species (r = − 0.31, p = 0.11; c). Correlation matrix of clinical parameters and microbial diversity markers showed only a limited number of significant associations (d). The sizes of the circles are dependent on the correlation coefficient value (r). Comparisons that did not achieve significance are represented with a gray circle. LOS represents the length of stay