In the 19th Century, industrialization and immigration caused a shift in population from rural to urban areas, which led to overcrowding and inadequate housing. Many urban residents had poor or no public water supplies and waste-disposal systems. These conditions caused repeated outbreaks of cholera, dysentery, TB, typhoid fever, influenza, yellow fever, and malaria. Such infectious diseases were controlled by local, state, and federal efforts to improve water supplies, wastewater disposal systems, and hygiene practices. Today, the same conditions exist in many developing nations, and CDC can play a major role in the transition. Full Article [2]