Outbreak!

In this activity, you will be learning about an outbreak of infectious Escherichia coli (E. coli) that occurred in the United States in 2009. E. coli are a large and diverse species of bacteria, some of which are harmless and reside in the intestinal tract of humans, while others cause disease by making a toxin called shiga toxin. Shiga toxin-producing E. coli (STEC) are usually transferred to humans when they eat foods contaminated with the STEC bacteria. The most common type of STEC bacteria is strain O157, which frequently causes bloody diarrhea, abdominal cramping, and hemolytic eremic syndrome (HUS), which is a type of kidney failure.

CDC Epidemic Intelligence Service (EIS) officers, or disease detectives, protect the public's health by serving the CDC, other public health agencies, and partners. One of the main activites of the EIS officers is to serve as responders to the CDC's Emergency Operations Center (EOC) or field site to provide epidemiologic assistance for disease outbreaks and other urgent public health threats. EIS officers' roles include conducting or participating in field investigations, conducting and interpreting epidemiological analyses, and writing public health updates to communicate timely information.


An outbreak investigation includes several steps, focusing on three questions: "what is the problem?", "what is the cause?", and "What can we do about it?" EIS officers follow these 12 steps when investigating an outbreak:

  1. Prepare for fieldwork

  2. Establish the existence of an outbreak

  3. Verify the diagnosis

  4. Construct a working case definition

  5. Find cases systematically and record information

  6. Perform descriptive epidemiology

  7. Develop hypotheses

  8. Evaluate hypotheses epidemiologically

  9. Reconsider, refine, and re-evaluate hypotheses.

  10. Implement control and prevention measures

  11. Initiate or maintain surveillance

  12. Communicate findings


Throughout the course of an outbreak investigation, EIS officers revisit many of the above steps, and they do not need to follow all the steps in chronological order. In this activity, you will be acting as an EIS officer, focusing on first determining the likely cause of the 2009 E. coli O157:H7 outbreak. Upon determining the cause, you will then develop a statement to be released to various audiences who need to be informed about the outbreak, describing how they should respond to the outbreak. In this scenario, you are a CDC Disease Detective tasked with the 2009 E. coli O157:H7.