This week’s Please Explain looks at the outbreak of fungal meningitis from contaminated steroid shots. We’ll find out how epidemiologists trace outbreaks like this to their origins and what compounding pharmacies are and how they work. Dr. Emil Hiesiger, clinical associate professor of neurology, NYU  School of Medicine, and Dr. William Schaffner, Professor of Preventive Medicine and Chair of the Department of Preventive Medicine at Vanderbilt University and president of the National Foundation for Infectious Diseases, explain.