Norovirus outbreak caused by a new septic system

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Patrons and employees of a new restaurant were affected by acute gastroenteritis (vomiting and diarrhea); initial tests were positive for fecal contamination. Investigators utilized a unique combination of epidemiological, microbial, and hydrogeological evidence that identified a new septic system as the source of the contamination.

Map showing dye detections in domestic wells in Door County, Wis.

Map showing point-to-point dye detections in domestic wells near the restaurant where the outbreak occurred, Door County, Wis. Potentiometric-level contours represent a hypothetical water-table surface showing which direction water would potentially flow, in meters above sea level.

In the summer of 2007, 211 patrons and 18 employees of a new restaurant in Door County, Wis., were affected by acute gastroenteritis (vomiting and diarrhea). Initial tests were positive for fecal contamination. Investigators utilized a unique combination of epidemiological, microbial, and hydrogeological evidence that eventually identified the septic system as the source of the contamination.

Step 1: Epidemiological studies identified that patients who had consumed water-based items like drinking water, ice, and salad washed at the restaurant were more likely to become ill. 

Step 2: LIDE performed the microbial investigation, evaluating water samples from restaurant taps, raw well water, and septic effluent using qPCR analysis to identify which pathogens were present and which water sources had been contaminated. LIDE also conducted norovirus sequencing which revealed that the norovirus in the well water was the same as the norovirus in the septic system and in the stool of infected patrons, suggesting a linkage between the groundwater from the septic system and the restaurant's drinking water.

Step 3: Hydrogeological studies utilized fluorescent dyes to track flow paths and travel times between the restaurant, septic system, and several local domestic wells. Both dyes were detected in the restaurant’s water supply well, showing that effluent from both the septic tanks and infiltration field was moving through the groundwater and reaching the restaurant’s well.

 

LIDE's role:

  • Rapid response to the outbreak provided timely sample collection and analysis
  • Worked collaboratively with State, County, and university departments and agencies to identify the source of the outbreak