Full Moon and Out-of-Hospital Cardiac Arrest in Japan　― Population-Based, Double-Controlled Case Series Analysis ―

Background: It is commonly believed that a full moon affects human behavior or the occurrence and outcome of various diseases; thus, the occurrence of out-of-hospital cardiac arrest (OHCA) might increase during full moon nights. Methods and Results: This nationwide, population-based observational study consecutively enrolled OHCA patients in Japan with attempted resuscitation between 2005 and 2016. The primary outcome measure was the occurrence of OHCA. Based on the double-control method, assuming Poisson sampling, we evaluated the average number of OHCA events that occurred on full moon nights compared with that which occurred on control nights, which included events that occurred on the same calendar days 1 week before and after the full moon nights. A total of 29,552 OHCA that occurred on 148 full moon nights and 58,707 OHCA that occurred on 296 control nights were eligible for analysis. The occurrence of OHCA did not differ between full moon and control nights (199.7 vs. 198.3 per night; relative risk [RR], 1.007; 95% CI: 0.993–1.021). On subgroup analysis, compared with control nights, the RR of OHCA occurrence were 1.013 (95% CI: 0.994–1.032, P=0.166) and 0.998 (95% CI: 0.977–1.020, P=0.866) for cardiac and non-cardiac origins, respectively. Conclusions: In this population, there was no significant difference in OHCA occurrence between full moon and control nights.