evidence: To further frustrate public-health authorities, the Spanish flu killed both directly and by leaving victims vulnerable to secondary infections with bacterial pneumonia, which was often fatal even in the absence of the flu, particularly in the elderly or infirm. This muddled the causality picture. But because the Spanish flu had proven so stunningly contagious and pneumonia was so often found during autopsies of flu victims, the federal Census Bureau decided to use a single category in its mortality statistics for 1918: "deaths from influenza and pneumonia (all forms)" (Mortality Statistics, 1918). As frustrating as it is to epidemiologists and life-insurance actuaries, all statistical studies of the effects of the 1918 pandemic are riddled with uncertainty and approximations. [...] Despite its early concerns, the Washington State Board of Health did not impose statewide measures to combat the pandemic until it was well under way, probably because it had very limited resources and little or no control over local health authorities. The only preventive regulation of statewide application that the board issued came on November 3, 1918, when it required that surgical masks of a specified size and thickness "entirely covering the nose and mouth" be worn in virtually all public places where people came into close contact with one another; the order also required that the proprietors of stores, restaurants, and cafes "keep their doors open and their places well ventilated" and that one-third of the windows in streetcars be opened when in use by the public ("Special Order and Regulation ... ").