Malaria is not very common in the late twentieth-century United States, but this photograph suggests to us that earlier in this century the disease posed enough of a threat for public health workers to concern themselves with it.

To determine exactly how substantial or common a problem malaria was, though, we need more information, and thus more sources. Local, state, and federal health agencies might have collected information on the incidence of malaria which we could use to determine how common or uncommon it was. Journals and books for professional health workers might describe anti-malarial campaigns undertaken by health departments, and thus tell us how common or uncommon it was for health officials to give out medication for this disease.