Waterborne Outbreak Basics

On this page:
What is an outbreak?
How do I know if an outbreak is occurring?
Waterborne infectious diseases that may cause outbreaks

What is an outbreak?

An outbreak is defined as an incident in which two or more persons experience a similar illness after a common exposure.

Waterborne outbreaks are classified in a variety of ways, including:

Confirmed Waterborne Outbreaks

• A confirmed waterborne outbreak is defined as an incident in which two or more persons experience a similar illness after having contact with the same source of drinking or recreational water and epidemiologic evaluation implicates the water as the source of illness. Confirmed outbreaks may or may not be laboratory-confirmed.
• Confirmed outbreaks may be classified as:
  1. Laboratory-Confirmed Agent: Outbreaks in which laboratory evidence of a specific etiologic agent is obtained.
  2. Epidemiologically Defined Agent: Outbreaks in which the clinical and epidemiologic evidence defines a likely agent, but laboratory confirmation is not obtained.
  3. Outbreak of Undetermined Etiology: Outbreaks in which laboratory confirmation is not obtained and clinical and epidemiologic evidence cannot define a likely agent.

Probable Waterborne Outbreaks

• A probable waterborne outbreak is defined as an incident in which two or more persons experience a similar illness after having contact with the same source of drinking or recreational water, and epidemiologic evaluation suggests that the water is the source of illness, but person-to-person transmission or other exposures cannot be ruled out.

How do I know if an outbreak is occurring?

An infectious disease outbreak is an increase in the occurrence of a particular infectious disease above what is normally expected. For example, a cluster of children absent from school due to gastrointestinal illness could represent an outbreak if they are found to have the same infectious disease.

Before concluding that an outbreak is occurring, it is important to get more information about the cases. The Minnesota Department of Health will typically contact the case (or the parents) and ask for information, such as the number of people who are ill, their symptoms, and a detailed history of places they went swimming, types of water they drank, and the foods eaten in the days before illness. It is also important to collect information on what diagnostic tests have been conducted and obtain their results.

Outbreaks may be caused by person-to-person transmission, contaminated food or water, or animal contact.

Waterborne infectious diseases that may cause outbreaks

Examples include:

• Cryptosporidiosis (Cryptosporidium)
• Escherichia coli O157:H7 Infection (E. coli O157)
  and Hemolytic Uremic Syndrome (HUS)
• Giardiasis (Giardia)
• Norovirus Infection (aka Norwalk virus, calicivirus, viral gastroenteritis)
• Shigellosis (Shigella)

For a list of more waterborne diseases see: Causes and Symptoms of Waterborne Illness