What Really Happened during the 1918 Influenza Pandemic? The Importance of Bacterial Secondary Infections

To the Editor—Plans for responding to an influenza pandemic are based on estimates of the effects that a 1918-like pandemic would have in modern populations and settings [1– 4]. Most recent descriptions of the 1918 pandemic emphasize the unique clinical expressions of the H1N1 pandemic strain—particularly the rapid progression to respiratory failure and death—and suggest that such cases were the predominant causes of death [1– 4]. Recent reviews have stated that most of the fatalities during the pandemic were due to respiratory failure with a characteristic hemorrhagic alveolitis [1], that the majority of these deaths were caused by a virus-induced cytokine storm that led to acute respiratory distress syndrome (ARDS),[2] that bacterial superinfections caused perhaps one-third of all deaths [1– 4], and that currently available antibiotics and bacterial vaccines would not be particularly useful should a 1918-like pandemic recur [1–3]. Given these views, it is not surprising that most plans for responding to an influenza pandemic minimize or disregard the importance of preventing and treating secondary bacterial infections. However, in their recent review, Mo-rens and Fauci noted that the causes of death during the 1918 pandemic were " similar to those during other pandemics " and that " most fatalities had secondary pneumonias caused by common bacteria or, in a minority of cases, ARDS-like syndromes " [5, table 1 on p. 1019]. Indeed , until recently, most descriptions of the 1918 pandemic (including nearly all contemporaneous reports) emphasized that fatal cases had variable and often prolonged clinical courses, that fulminant cases with rapid progression were relatively uncommon, and that secondary bacterial infections were the likely causes of most deaths. The following descriptions from Great Britain, the United States, and New Zealand are illustrative. Great Britain. In their review of the 1918 pandemic, medical leaders in Great Britain at the time concluded that the clinical courses of fatal cases were highly variable and that bacterial infections were the predominant causes of death. A report from 1920 noted that " pneumonic complications . .. would develop at any period of the influenza attack; there was no rule " [6, p. 71]. Regarding bacterial infections , the report stated that " the organisms responsible for the infections of the respiratory tract, to which its chief terrors are due, are well known. They are Pfeiffer's bacillus [now known as Hae-mophilus influenzae], the pneumococcus, streptococci, and especially streptococci of hemolytic type, and more occasionally staphylococci, …