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What is A local restaurant was the focus of a botulism outbreak.
The state epidemiologist most likely used which format to determine the cause of the disease? and explain in detail?
Cross-sectional studies (Prevalence studies) 
The simplest in concept and execution is the cross-sectional study. In this, a set of individuals are chosen who may be a representative sample of the general population or of people in a particular community or a sample of members of some special subgroup - school children, the armed forces, workers in a particular industry, etc. The measurements of exposure and effect are made at the same time providing information on the relationship between a disease and other variables of interest, as they exist at one point of time. Cross-sectional studies are relatively easy and economical to carry out. 
Reference: Essentials of Preventive and Community Dentisitry, Soben Peter , 4th ed page no 57