Opportunistic Pathogens (OPs): #1 cause of waterborne diseases in the United States

We have long known about the dangers associated with waterborne pathogens. Fecal contamination of drinking water sources can lead to gastrointestinal illness and deaths caused by a variety of waterborne pathogens. We control for these risks by 1) selecting clean water sources for treatment, 2) treating the water to remove particles and bacteria by filters, and 3) disinfecting water with chlorine. Treatment plants have to prove they are meeting very high standards in protecting the public from this danger, by frequently measuring filter efficiency and chlorine levels at the treatment plant. In addition, utilities also have to double-check their control of this threat, by sampling their water pipelines for indicator bacteria which are present at very high concentrations in feces, such as coliforms and E. coli, and also maintaining significant levels of chlorine as water is transported to homes.

In recent decades, we have also come to recognize that fecal contamination is not the only source of waterborne pathogens in our drinking water. These other bacteria do not come from fecal contamination, but rather they grow in pipes and homes themselves, and are commonly referred to as Opportunistic Pathogens, or OPs for short. The presence of OPs in drinking water is a danger that is not directly addressed by existing Federal Regulations, despite the fact that an OP, Legionella pneumophila is now known to be the most frequently reported causative agent of waterborne disease outbreaks (and deaths) in the United States.

The impacts that OPs can have on human health are numerous, and they generally do not come from drinking the water. For example, Legionella pneumophila (the bacterium which causes Legionnaire’s disease) and Mycobacterium avium live in pipes, and human exposure occurs when consumers breath tiny water droplets in the air from showers or washing hands. Staphylococcus aureus can lead to skin infections when it contacts open cuts or existing irritations. Pseudomonas aeruginosa can lead to a variety of infections: lung and blood stream infections, skin irritations, and infections of the eye or ear.

Legionella bacteria (Image courtesy: CDC)
Legionella bacteria (Image courtesy: CDC)

Most OPs are not regulated or routinely measured in drinking water. Legionella is only regulated in water as it leaves the treatment plant, which is the location that is least likely to have high levels of Legionella, and the regulation does not do enough for public health protection. However, the conditions which are associated with a typical building’s plumbing, can create ideal conditions for these bacteria to take hold, such as warm water, so Legionella can be present at very high levels in homes even when it is not detected at the treatment plant.

Residents of Flint have also reported many symptoms (see, here, here and here) which are consistent with those associated with some infections caused by waterborne OPs, such as skin irritations. However, it is unclear whether OPs may be contributing to this problem due to a lack of water testing, and difficulties in linking human health problems to water exposure. There is some indication that in March 2015, the Health Department was exploring possible links between drinking water and cases of Legionnaire’s disease in Genesse County.

Additional water testing targeting OPs, particularly of samples collected at the point of use within homes, could offer valuable information regarding the microbial water quality of the drinking water available to residents of Flint.

Primary Author: Emily Garner

Acknowledgements: Dr. Marc Edwards, Dr. Brandi Clark and William Rhoads

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