Exceptionally high mortality rate of the 1918 influenza pandemic in the Brazilian naval fleet

BACKGROUND The naval experience with the 1918 pandemic during World War I remains underexplored despite its key role on the pandemic's global diffusion and the epidemiological interest of isolated and relatively homogeneous populations. The pandemic outbreak in the Brazilian naval fleet is of particular interest both because of its severity and the fact that it was the only Latin American military force deployed to war. OBJECTIVES To study the mortality patterns of the pandemic in the Brazilian fleet sent to patrol the West African coast in 1918. METHOD We investigated mortality across vessels, ranks, and occupations based on official population and mortality records from the Brazilian Navy Archives. RESULTS The outbreak that swept this fleet included the highest influenza mortality rate on any naval ship reported to date. Nearly 10% of the crews died, with death rates reaching 13-14% on two destroyers. While overall mortality was lower for officers, stokers and engineer officers were significantly more likely to die from the pandemic, possibly due to the pulmonary damage from constant exposure to the smoke and coal dust from the boilers. CONCLUSIONS The fatality patterns observed provide valuable data on the conditions that can exacerbate the impact of a pandemic. While the putative lack of exposure to a first pandemic wave may have played a role in the excessive mortality observed in this fleet, our results indicate that strenuous labor conditions, dehydration, and exposure to coal dust were major risk factors. The unequal death rates among vessels remain an open question.