A month after the earthquake, Haiti is now threatened by another devastating public health disaster -- epidemics of infectious diseases and untreated chronic illnesses in squatter communities where tens of thousands of people are crowded together with no sanitation facilities and little access to clean water and food.

Early one morning under an already scorching sun, a team of about 50 doctors, nurses, pharmacists, and lab technicians from Zanmi Lasante, PIH's sister organization, drove to an open field adjacent to one of these informal settlements--a patchwork of shelters pieced together from tattered sheets of cloth, cardboard, and scraps of wood, with an estimated population of 40,000. Watch a slideshow below.

Within 45 minutes, the Zanmi Lasante team had erected a large tent, filled most of it with tables and chairs for 20 consulting stations, created and stocked a small pharmacy and lab, and established an orderly system for checking patients in and sending them to the next available doctor. Over the next six hours, they saw and treated more than 500 patients -- children with coughs and diarrhea, adults with wounds and fevers, an elderly woman with diabetes who went into shock and was rushed to a hospital.

Zanmi Lasante has been doing exactly this kind of work--working in partnership with the residents of destitute communities to provide quality health care and essential social services--for over 25 years.