Explain how we know that ancient civilizations knew of and were concerned of infectious diseases

We can be sure that ancient civilizations knew of and were concerned about infectious diseases from several facts. The hunter gatherers rarely suffered from water borne diseases. They knew that the water that stank or did not taste well was not good to intake. Their main knowledge came from experience. During the Greek period several doctors like Alcmaeon of Croton were mentioned and hence they must have had the knowledge about infectious diseases like Cholera. Several other infectious disease treatment have also been mentioned during the Greek period.