Estimating case fatality ratios from infectious disease surveillance data

Understanding the virulence of an emerging infectious disease can help direct resources during an outbreak response. The case fatality ratio, a measure of virulence, is the fraction of cases who die after contracting a disease. Incomplete reporting of the number of infected individuals, both recovered and dead, can lead to biased estimates of the case fatality ratio. We propose a simple estimator for the relative case fatality ratio which controls for reporting rates that may vary across time and is asymptotically unbiased. We generalize our methods to account for elapsed time between infection and death. We conduct a simulation study to evaluate the performance of our methods in realistic outbreak scenarios. Our new methods could provide valuable information about vulnerable subgroups of a population early in an outbreak of an emerging pathogen such as a pandemic influenza virus.