The 1918 influenza pandemic in Florianopolis: a subtropical city in Brazil

Few studies have addressed the impact and dynamics of the 1918-1919 influenza pandemic in tropical and sub-tropical areas. To help cover this gap, we analyzed all death certificates issued from October 1913 to June 1921 in Florianopolis (Brazil), a subtropical state capital with a population of 41,298 inhabitants in 1920. In November and December 1918 (spring) there were a total of 70 and 14 deaths due to influenza and pneumonia, respectively, in contrast to a mean annual mortality attributed to these causes of 8.1 deaths, usually concentrated between January and August (summer to winter). We also determined the mortality burden due to the pandemic through the analysis of excess mortality during the pandemic period against the baseline mortality in the same months from other years. We obtained a total of 127 deaths (0.33% of the total population), nearly twice the number of deaths documented by death certificates from this period. No other influenza pandemic waves were detected in earlier or subsequent months. Our results confirm the observed patterns of age-shift in mortality in pandemic scenarios, with young adults as the most affected age-group. The pandemic in Florianopolis was further characterized by some specific outcomes: (1) there was a discrete peak in mortality due to renal causes in the initial phase of the pandemic; (2) pandemic influenza did not affect the number of reported bronchitis and bronchiolitis deaths (unusually high in the year preceding the pandemic); and (3) the mortality burden was proportionally lower in Florianopolis than in large urban centers such as São Paulo and Rio de Janeiro. We suggest that this latter outcome was the result of an effective and prompt network of voluntary solidarity assistance (as endorsed by contemporaneous documents), which was probably more difficult to implement in larger metropolis.