Waterborne Outbreak Investigations

Waterborne illness outbreak investigations involve coordination between epidemiologists and environmental health specialists (health inspectors). Environmental health specialists focus on evaluating the water safety practices at the body of water where the outbreak likely occurred, interviewing employees, and collecting environmental samples. Epidemiologists coordinate patron interviews, arrange stool sample collection and testing, and perform data analysis to help determine if there is a specific body of water or activity that made people sick.

This model of disease outbreak investigation, with a core group of epidemiologists and an extensive network of environmental health specialists (in coordination with local, state and federal health agencies), provides Minnesotans with an efficient waterborne disease surveillance system.

During an investigation, it is important to interview patrons who were ill, as well as those who did not get ill. Information obtained from patrons during an investigation may include:

• Demographic information
• Illness history, including when illness started and symptoms
• Exposure history, including details about places where swimming occurred and food and beverages consumed
• In addition, stool samples may be requested from ill individuals in order to identify the pathogen that is causing the outbreak

Investigation of a recreational water facility may include:

• Illness histories from recreational water employees to identify whether a staff member may have contributed to the outbreak or became ill while working
• Collection of water samples
• An assessment of facility records, practices, and policies to determine if a procedure may have contributed to the outbreak
• Any necessary corrective measures such as hyperchlorinating pool water, repairing a failed septic system near a beach, restricting ill employees from work until they are recovered from illness, and modifying unsafe water treatment practices and procedures

Investigation of a drinking water source may include:

• Collection of water samples
• Physical inspection of the drinking water system
• Review of recent water quality data
• Determination if any recent events occurred at the drinking water system that might have caused the water to be contaminated, such as  repairs, system failures, vandalism or unauthorized access, or drops in system pressure
• Any necessary corrective measures such as repairing a broken drinking water system, repairing a failed septic system near a well, or modifying unsafe water treatment practices and procedures