A measure of the severity of an epidemic and its burden on the healthcare system is the excess number of hospital visits and hospitalized patients during the epidemic and during the post-epidemic years. Yearly excess numbers of outpatients, in-patient hospitalizations (abbreviated to "hospitalization" hereafter), and all-cause deaths reported by the large public hospital and the public medics system during 1918-1920 were computed by the method of Serfling et al. [16] . We first computed the yearly mean numbers of outpatients, hospitalizations, and all-cause deaths over the two adjacent baseline years before the epidemic (1916, 1917) and the two adjacent baseline years after (1921, 1922) . We then subtracted these means from the corresponding yearly numbers of outpatients, hospitalizations, and all-cause deaths for each year during 1918-1920 to obtain the yearly excess numbers during 1918-1920. A yearly excess number is considered to be statistically significant if the number (of outpatients, hospitalizations, or allcause deaths) for that pandemic year exceeds the corresponding mean of the adjacent baseline years of 1916, 1917, 1921 , and 1922 by 2 SDs or more [9] . In order to compare the yearly excess healthcare burden of the pandemic years of 1918-1920, we computed the percentages of these yearly excess numbers over the means of the adjacent baseline years, to ascertain the impact of the pandemic on the healthcare system during each of the years in 1918-1920.