An Outbreak of Gastrointestinal Illness Following a Church Supper ("Oswego")

This case study is based on an investigation conducted by the New York State Department of Public Health Division. The case study was developed by Wendell Ames, MD, Stafford Wheeler, MD, and Alexander Langmuir, MD in the early 1940s.  It has been substantially updated and edited since then by Philip Brachman, Michael Gregg, and Richard Dicker, with input from the many instructors who have reviewed and taught "Oswego" as part of the EIS Summer Course each year. 
Date published
Oct, 2012
Last updated
21 Jan 2020


S. aureus outbreak among church picnic attendees, 1940; the classic, straightforward outbreak investigation in a defined population.


  • Define the terms “cluster,” “outbreak,” and “epidemic”
  • List the steps in the investigation of an outbreak
  • Draw, interpret, and describe the value of an epidemic curve
  • Calculate and compare food-specific attack rates to identify possible vehicles
  • List reasons for investigating an outbreak that has apparently ended