Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems. At the local level, this means keeping track of the incidence or the number of new cases of specific diseases and describing how often these diseases occur in the community and who is affected by them. Once suspected or confirmed cases of certain infectious diseases are identified by a physician, school nurse, laboratory, etc., Ohio law requires that they be reported to the local health department so that contacts of the case can be protected and further spread of the disease can be prevented. Trends are monitored, and potential outbreaks are investigated, with the ultimate goal of finding the source and stopping the spread of disease. For instance, when a foodborne outbreak or an influenza outbreak attacks the community, the epidemiologist begins an investigation. Field work is done to determine potential sources of the disease, how the disease is spread, what the risks are, who is at risk, and how to prevent additional incidences from occurring.