Age-specific mortality patterns and transmissibility during the 1889-90 influenza pandemic in Madrid, Spain.

Abstract

Purpose: Although the 1889e1890 influenza pandemic was one of the most important epidemic events ofthe 19th century, little is known about the mortality impact of this pandemic based on detailed respi-ratory mortality data sets.Methods:We estimated excess mortality rates for the 1889e1890 pandemic in Madrid from high-resolution respiratory and all-cause individual-level mortality data retrieved from theGazeta deMadrid, the Official Bulletin of the Spanish government. We also generated estimates of the reproductionnumber from the early growth phase of the pandemic.Results:The main pandemic wave in Madrid was evident from respiratory and all-cause mortality ratesduring the winter of 1889e1890. Our estimates of excess mortality for this pandemic were 58.3 per10,000 for all-cause mortality and 44.5 per 10,000 for respiratory mortality. Age-specific excess mortalityrates displayed a J-shape pattern, with school children aged 5e14 years experiencing the lowest respi-ratory excess death rates (8.8 excess respiratory deaths per 10,000), whereas older populations agedgreater than or equal to 70 years had the highest rates (367.9 per 10,000). Although seniors experiencedthe highest absolute excess death rates, the standardized mortality ratio was highest among youngadults aged 15e24 years. The early growth phase of the pandemic displayed dynamics consistent with anexponentially growing transmission process. Using the generalized-growth method, we estimated thereproduction number in the range of 1.2e1.3 assuming a 3-day mean generation interval and of 1.3e1.5assuming a 4-day mean generation interval.Conclusions:Our study adds to our understanding of the mortality impact and transmissibility of the1889e1890 influenza pandemic using detailed individual-level mortality data sets. More quantitativestudies are needed to quantify the variability of the mortality impact of this understudied pandemic atregional and global scales.