Month of discontinuity (2012; during or after month exposed, otherwise unexposed) Incidence rate ratio (95% CI) March 1.71 (0.75 to 4.03) April 1.13 (0.52 to 2.53) May 0.54 (0.26 to 1.13) June 0.55 (0.27 to 1.14) July 0.61 (0.30 to 1.25) August 0.62 (0.31 to 1.27)

Table 2: Incidence rate ratios associated with a step change (regression discontinuity) in the number of monthly counts of L. pneumophila serogroup 1. CI: confidence interval.