From 1545 to 1550, a deadly epidemic in what is today southern Mexico killed between five and fifteen million Aztec people. The exact cause or causes has been a mystery for the past 500 years, but now a new study suggests the outbreak could have been caused by a deadly form of salmonella. Researchers in the study tested 500-year-old DNA embedded in the teeth of 24 indigenous individuals' remains. Of the 24 that were tested, 10 showed signs of salmonella. According to study author Ashild Vagene, the salmonella strain is a bacterial infection that causes a type of fever nearly identical to typhoid. Any food or water contaminated with the strain would have turned deadly once ingested. Victims would have experienced a fever, vomiting and likely a rash. To really confirm that salmonella contributed to the historical outbreak in Mexico, scientists would need to test more DNA from different sites. Vagene agrees that for now, researchers can only hypothesize about what caused the massive outbreak.