Hello! The most fatal disease I’ve studied in depth would be hepatitis C virus. This is mainly because two of the other microbes I work on, norovirus and Campylobacter, are both types of self-limiting diseases – meaning that in most cases you’ll get better without treatment in about a week.
So, how fatal is hepatitis C? Well, it affects over 150 million people worldwide, and there are three to four million new cases each year. It is one of the major causes of progressive liver disease, with 350,000 liver-related deaths per year, and one of the most frequent reasons for needing a liver transplant. In the USA, it is the most common chronic (long-term) infection, affecting up to 3 million individuals (about 1% of the population), with an estimated 8,000 to 10,000 deaths each year and an annual cost of $744 million (£438 million).