The number of L. pneumophila -containing neutrophils correlates with data obtained by plating for CFU. Mice were infected with 2.5 × 106 CFU of L. pneumophila per mouse. Lungs were harvested at various times after infection and divided into two halves. One half was analysed for the presence of neutrophils that contained intracellular L. pneumophila by flow cytometry while the other was used to determine L. pneumophila CFU. Data from the two different methods were plotted and analysed for correlation by determining the Spearman’s rank correlation coefficient (rs) and statistical significance (p). Each circle represents the bacterial load in the whole lung for a single mouse. Each panel is a combination of 2 to 5 independent experiments with a range of 4 to 10 mice per experiment.