In March 2016, we sampled tap water from 5 homes and 6 small businesses in Flint, with ALL testing culture-negative for Legionella. We used a standard culture-method often used by hospitals to determine if there is a risk of Legionnaire’s Disease outbreak. This is good news. We will be following up with another sampling this summer when the weather is warmer and there is more of a tendency of Legionella bacteria to grow.
We are also examining the water samples we have collected more closely using DNA-based methods. The DNA methods may help us detect lower levels of Legionella that we couldn’t see with culture and also identify different kinds of Legionella, but the trade-off is that we will not be able to tell the difference between live and dead bacteria. That is why the culture method is considered the standard for determining risk of getting Legionnaires’ Disease from tap water.
Using the best available science, the sampling we performed in March 2016 showed that if any living Legionella were present, their levels were low the day of testing. There is always some risk of Legionnaire’s Disease from tap water, but our current results from March suggest the risk was not concerning at any of our sample sites in Flint. We will remain vigilant in our tracking and testing of this potential problem in Flint homes.
We have been getting questions from concerned parents about the Legionella announcement made earlier today and if there is a risk to taking showers.
1. Is it safe for me and my kids to shower in the water now?
A. We agree with DHHS that this problem, is probably behind us all, even it if was caused by the Flint River water. It is safe to shower now whether you are an adult or a child. When we say “safe,” we mean it is no riskier to shower in Flint now than in any other U.S. city.
2. Is this (was this) a risk only in high-rise buildings or plumbing systems in small homes can harbor Legionella pneumophila too?
A. During August of 2015 we focused our Legionella testing on residences and smaller buildings like McDonald’s throughout the city. Despite looking as hard as we could, we could find no trace of the Legionella bacterial strain that causes disease. So in homes and small buildings at least, based on our data, the risk of exposure was relatively low. We published those data on our website earlier in the year, and frankly, we were a little surprised there was not more Legionella.
However, just before the switch back to Detroit, we sampled larger buildings, and we found very high levels of the types of Legionella that cause disease. So we tend to feel, that the risk of exposure, was much higher in the bigger buildings.
3. The water has been “bleachy” in the last few days. Is that a risk?
A. This is actually a good sign that your risk of Legionella very low. The “bleach” or chlorine actually kills Legionella bateria.
Acknowledgements: Dr. Amy Pruden, Dr. Marc Edwards, Siddhartha Roy
A key hypothesis of our National Science Foundation RAPID grant is that the rapid corrosion of iron water mains in Flint would dramatically increase growth of Legionella in buildings. Mechanistically, higher rates of iron corrosion will produce: 1) higher iron in water, and 2) lower levels of free chlorine. Both of these factors were confirmed to be present in Flint during our field sampling, and have been shown to dramatically increase Legionella regrowth in our recently published laboratory research utilizing simulated distribution systems.1-5
Additional research is needed to examine the basis of this relationship.
Masters, S., and M. Edwards. Increased Lead in Water Associated with Iron Corrosion. Environmental Engineering Science, (2015), 32 (5), 361-369.
Masters, S.M., Wang, H., A. Pruden and M. Edwards. Redox Gradients in Distribution Systems Influence Water Quality, Corrosion, and Microbial Ecology. Water Research, (2015), DOI: 10.1016/j.watres.2014.09.048.
Wang, H., Masters, S., Edwards, M.A., Falkinham, J.O. III, and A. Pruden. Effect of Disinfectant, Water Age, and Pipe Materials on Bacterial and Eukaryotic Community Structure in Drinking Water Biofilm. Environmental Science & Technology. dx.doi.org/10.1021/es402636u.
Wang, H., S. Masters, Y Hong, J. Stallings, J.O. Falkingham, M. Edwards and A. Pruden. Effect of disinfectant, water age, and pipe material on occurrence and persistence of Legionella, mycobacteria, Pseudomonas aeruginosa, and two amoebas. Environmental Science & Technology 46 (21), 11566-11574 (2012).
Wang, H., Masters, S.; Falkinham, J.O.; Edwards, M.; and A. Pruden. Distribution System Water Quality Affects Responses of Opportunistic Pathogen Gene Markers in Household Water Heaters. Environmental Science & Technology. (2015), DOI: 10.1021/acs.est.5boa.538
Dr. Otto Schwake, Min Tang, and Ni “Joyce” Zhu are in Flint sampling the water for opportunistic pathogens, iron and lead before the switch to Detroit water. We will post an update on what we find very soon. Meanwhile, here is a photograph Joyce took when sampling water inside a Flint Hospital. We hope this is the last time we find something like this in a hospital or home in Flint.
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.
Here we report on our results for several additional OPs, alongside the previous results, based on presence of DNA markers specific to each bacterium. Pathogenic species are indicated in red. Mycobacterium spp. represents a genus of bacteria that includes several pathogenic and non-pathogenic species. Vermamoeba vermiformis is of interest because it is an amoeba that may play an important role in the life cycle of some pathogens, such as Legionella pneumophila. In addition, we attempted to culture pathogenic Staphylococcus species from the samples.
Table 1 demonstrates that we did not detect quantifiable levels of Pseudomonas aeruginosa, Legionella pneumophila, orMycobacterium avium in water or biofilm samples collected from any of the sixteen sites in Flint. Acanthamoeba polyphaga was found in the biofilm at 3 sites in Flint. Acanthamoeba polyphaga is an amoeba that is often associated with eye infections of individuals using tap water for contact lens care rather than sterile saline, but has also been associated with skin and respiratory infections. More information on this amoeba can be found here.
Water from each site was also cultured using methods specific to growing Staphylococcus. Only two sites resulted in Staphylococcus growth. DNA from 10% of the resulting colonies were sequenced to identify the species. All sequences were identified to belong to either Staphylococcus epidermidis or Staphylococcus hominis. Both species are frequently found on the skin of healthy individuals and are not typically pathogenic.
Although the number of samples collected has been small and were collected from each site on a single date, our results do not indicate the presence of pathogenic OPs in Flint water, with the exception of sporadic detection of Acanthamoeba polyphaga in biofilm samples. Overall, this limited sampling, indicates that from a microbiological perspective Flint water does not seem to pose a health risk worse than many other U.S. cities that we have sampled. However, the chronically low chlorine residuals throughout the distribution system, suggest that this issue should be the subject of continued scrutiny.
Additional Notes: The method we used to quantify the pathogens is called quantitative polymerase chain reaction (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 OPs detection.
Analysis and write-up: Emily Garner
Acknowledgements: Dr. Marc Edwards and Dr. Amy Pruden