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In November and December of 2022, the Weld County Public Health Department consulted with CDPHE about an unusual number of cases of Legionnaires Disease occurring in a relatively small area. There were five reported cases of the illness and case interviews were completed for four of the five affected people. Excerpt from the internal communications at the time:
"We have recently seen a notable increase in reported legionella infections in Weld County – five cases in the last 12 days. Of the three most recent cases, two live within two miles of each other and one lives within seven miles of the other two. We have not yet found any evidence of linked exposures."
In a situation where a cluster of illnesses is identified and there is a potential for the root cause of the illness to be drinking water, public health partners work with the Safe Drinking Water Program here at CDPHE to assess the likelihood/possibility that the drinking water is the root cause of the cluster (or waterborne disease outbreak).
What was the Response?
Based on initial interviews with the ill folks, the county determined that there appeared to be a lack of common exposures that are usually seen. Typically in a legionella outbreak, you may find that all infected people used the same recreation center hot tub or shop at the same grocery store that has vegetable misters running.
The county and state epidemiologist group then reached out to the Safe Drinking Water Program staff to check the known addresses of the ill people to see if they were served by the same water system and if it was possible that a contamination event had occurred at that specific water system. We specifically were trying to determine whether there had been any service disruptions, major construction projects, water main breaks, or other events related to the water utilities that service these individuals' residential areas.
The Safe Drinking Water Program then interfaced with water system operational staff to confirm whether there had been any water quality issues in these areas. Also, it was determined that these homes- while being in proximity to each other, were served by four different water providers. All providers demonstrated robust chlorine residuals and were able to show a lack of bacteriological contamination in their drinking water.
While the specific cause of this outbreak was never determined, public drinking water was eliminated as a source.
What can a water operator do to prepare for such an event?
If a cluster of illnesses occurs in your service area, you may be called upon to produce records of treatment and distribution system water quality in order to eliminate any potential that your drinking water caused the illnesses.
Maintaining treatment plant records is standard procedure for most public water systems. However, having a comprehensive distribution system microbial sampling that goes beyond the minimums of the total coliform rule is more rare. Consider developing water quality sampling starting with distribution system basic water quality parameters like chlorine residual, pH, turbidity and heterotrophic plate count. This will help provide assurance that your distribution system water quality is not the cause of a legionella outbreak. Also, water sampling for legionella can be done on a quarterly or semi-annual basis to provide further assurances to the public that the drinking water quality you provide to your customers is safe and relatively pathogen free.
➽ Tyson Ingles, Lead Drinking Water Engineer
