INTRODUCTION:Worldwide, the COVID-19 epidemic has put health systems to the test. The excess mortality is partly due to the influx of patients requiring hospitalization and intensive care. We propose that the chronology of epidemic spread gives a window of time in which hospitals can act to prevent reaching capacity. METHODS:The out-of-hospital SAMU Emergency Medical System in an entry point into the French health care system. We recorded the number of patients managed, of patients transferred to emergency departments (ED), and of mobile intensive care units (MICUs) dispatched. Each criterion was compared to the mean of the same criterion over the previous 5 years. The alert threshold which indicated a public health crisis was defined as a 20% increase compared to the 5-year mean. RESULTS:The reference period, from January 2015 to December 2019, included 3 381 611 calls, and 1 137 856 patients. The study period, from 17 February to 28 March 2020, included 166 888 calls, and 56 708 patients. The daily numbers of patients managed crossed the threshold on February 25, and increased until the end of the study period. The daily number of patients transferred to ED crossed the threshold on March 16, and increased until the end of the period. The daily number of MICUs dispatched crossed the threshold on March 15, and increased until the end of the period. CONCLUSION:The COVID-19 epidemic reached our department in three consecutive waves which overwhelmed the health care system. The first wave preceded by 30 days the massive arrival of critical patients. Health care systems must take advantage of this delay to prepare for the third wave.