Uncertainty is at the heart of disease outbreaks. There is so much we don’t know. Which pathogen is the culprit, how deadly is it, how many people are infected? New information comes in small pieces, and needs to be verified. But how? In early February, news spread on Twitter that a doctor — one of the eight who had been reprimanded weeks earlier by Chinese authorities for sounding the alarm about a new disease — had died. But was it true?