Calculating mortality rates during a disease epidemic is fraught with pitfalls. “What you can safely say is that if you divide the number of reported deaths by the number of reported cases, you will almost certainly get the wrong answer,” said John Edmunds, a professor at the center for mathematical modeling of infectious diseases at the London School of Hygiene & Tropical Medicine. “In an unfolding epidemic, it can be misleading to look at the naïve estimate of deaths so far divided by cases so far,” said Christl Donnelly, a disease specialist at Oxford University and Imperial College London.
