As developing countries continue to undergo massive urbanization, the simultaneous increase of slums presents ideal thriving grounds for contagious and infectious illnesses. This is in spite of the reasoning that the creation of cities would create easier means of healthcare access and service, in comparison to rural areas. One of the contributing factors to facilitated epidemics is city-crowding, along with poor or a complete lack of housing. This is observed in slums in particular, with a great number of not only citizens, but migrants living there. According to the United Nations Human Settlement Program, UN-Habitat, approximately 33% of the developing world's population lives in slums (863 million people).  It was observed through the recent spread of the Zika virus that crowding can effectively move from slums to entire countries. Interventions in both public healthcare and housing must be made in order to prevent the spread of infectious diseases, as well as the possibility of it spreading on a global scale.