[During 1519] the plague began, oh my sons! . . . It was truly terrible, the number of dead there were in that period. . . . [In 1521] the plague began to spread. . . . The people could not in any way control the sickness. . . . Great was the stench of the dead. . . . The dogs and the vultures devoured the bodies. The mortality was terrible. Your grandfathers died, and with them died the son of the king and his brothers and kinsmen. . . . [In 1560] the plague which had lashed the people long ago began [again] here. . . . [A] fearful death fell on our heads . . . Now the people were overcome by intense cold and fever . . . then came a cough growing worse and worse . . . and small and large sores broke out on them. The disease attacked everyone here. . . . Truly it was impossible to count the number of men, women, and children who died this year. My mother, my father, my younger brother, and my sister, all died.
Berdardino de Sahagún, Florentine Codex (1500s)
The Florentine Codex was originally compiled by Fray Bernardino de Sahagún as Historia general de las cosas de nueva España (General history of the things of New Spain) in 1529. While de Sahagún learned and recorded the culture of the Aztecs, he did so primarily in order to better understand how to convert them to Christianity. However, his work provides an important insight into the daily life of the Aztecs in the first decade after the Spanish arrival.
But before the Spaniards had risen against us, first there came to be prevalent a great sickness, a plague. It was in Tepeilhuitl that it originated, that there spread over the people a great destruction of men. Some it indeed covered [with pustules]; they were spread everywhere, on one's face, on one's head, on one's breast, etc. There was indeed perishing; many indeed died of it. No longer could they walk; they only lay in their abodes, in their beds. No longer could they move, no longer could they bestir themselves, no longer could they raise themselves, no longer could they stretch themselves out face down, no longer could they stretch themselves out on their backs. And when they bestirred themselves, much did they cry out. There was much perishing. Like a covering, covering-like, were the pustules. Indeed many people died of them, and many just died of hunger. There was death from hunger; there was no one to take care of another; there was no one to attend to another.