Geographic variables play an important role in the study of epidemics. The role of one such variable, population density, in the spread of influenza is controversial.
Prior studies have tested for such a role using arbitrary thresholds for population density above or below which places are hypothesized to have higher or lower mortality. The results of such studies are mixed.
The objective of this study is to estimate, rather than assume, a threshold level of population density that separates low-density regions from high-density regions on the basis of population loss during an influenza pandemic. We study the case of the influenza pandemic of 1918--19 in India, where over 15 million people died in the short span of less than one year.
Pandemic recombinant influenza virus graphic from Russell Kightley Media