Results from Field Sampling in Flint (Aug 17-19 2015) : Opportunistic Pathogens

Report 3. Opportunistic Pathogens: Legionella pneumophila and Mycobacterium avium.

During our recent sampling trip to Flint, we found that all of our samples sites were free of fecal indicator bacteria but that many sites lacked a chlorine residual, which is a critical barrier for preventing regrowth of bacteria in pipes. Our research team has further observed in previous work that opportunistic pathogens tend to grow in distribution system and home plumbing pipes when there is a lack of chlorine residual. Thus, it is worrisome that recent reports in Genesee County indicate a possible increase in cases of Legionnaire’s Disease, a respiratory infection caused by an opportunistic pathogen (Legionella pneumophila).

During our trip, we collected samples from nine businesses located throughout the city of Flint, including eight of Flint’s designated monitoring sites and a business located in close proximity to the drinking water treatment plant, and seven homes of Flint water consumers. For comparison, we also collected water from four businesses that receive water from Detroit. At each of these sites we collected both water samples and swabs of bacteria growing on the surface within the faucet, known as the biofilm.

From these samples, we investigated the presence of two key opportunistic pathogens which are important to public health: Legionella pneumophila and Mycobacterium avium. We also measured the presence of a DNA marker specific to all bacteria within the Legionella genus. This Legionella genus is a category of bacteria which includes several pathogenic (e.g. Legionella pneumophila) and several non-pathogenic species.

Results: We did not detect quantifiable levels of Legionella pneumophila or Mycobacterium avium in water or biofilm samples collected from any of the sixteen sites in Flint or in any of the four sites receiving Detroit water.

We detected bacteria belonging to the Legionella genus in water collected from two of the nine businesses/monitoring sites and in five of seven citizen homes. Legionella genus was not detected in any of the four samples collected from sites receiving Detroit water.

Conclusion: We found no evidence of Legionella pneumophila or Mycobacterium avium present at the time of sampling at the sites tested. However, we hypothesize that the presence of bacteria belonging to the Legionella genus may be indicative of conditions in the distribution system or in the plumbing of tested homes that may be favorable to the growth of the pathogenic species, Legionella pneumophila. In particular, the chronically low levels of a chlorine residual in many parts of the distribution system are likely to increase the risk of opportunistic pathogen colonization.

Additional Notes: The method we used to quantify these pathogens is called quantitative polymerase chain reaction (or qPCR). It works by detecting DNA specific to the target microorganisms, making the method very specific, but also very sensitive, as an organism does not necessarily need to be alive or culturable for us to identify that it is present. The minimum threshold of target bacteria, or more accurately the bacteria’s DNA that must be present in the 1-liter samples that we collected is 10 DNA copies per mL or 104 copies in the entire swabbed biofilm. This is the best available and most sensitive method of Legionella detection.

Sample analyses and write-up: Emily Garner

Acknowledgements: Dr. Marc Edwards and Dr. Amy Pruden

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