Study: MRSA In Waste Water Treatment Plants

 

Photo Credit USGS – Wastewater: The Primary Treatment Process

1. Screening 2. Pumping 3. Aerating 4. Removing sludge 5. Removing Scum 6. killing bacteria

 

 

# 6699

 

While it may not seem (or even be) glamorous, there are scientists who spend considerable time examining the input and output of wastewater (sewage) treatment plants. Given the potential environmental impact of the discharges from these facilities, it is important work.

 

The subject of wastewater treatment plants - and the substances that their processes can fail to remove during treatment - has come up before in this blog.

 

In 2007, with governments around the world stockpiling large quantities of Tamiflu (Oseltamivir) in anticipation of a pandemic, concerns turned to what would happen if millions of doses were dispensed, consumed, and excrete by humans into the waste water system in a short period of time.

 

In The Law of Unintended Consequences we looked at a report in Environmental Health Perspectives (EHP) called Potential Risks Associated with the Proposed Widespread Use of Tamiflu that found enough of excreted oseltamivir carboxylate (OC) would survive treatment, and be ejected into the environment, to raise concerns.

 

In October of 2009 and we saw another report (see Everything Old Is News Again), based on studies done the previous year in Kyoto, Japan – that showed elevated levels of the OC Metabolite in wastewater discharge. 

 

In 2011, in Pandemics & The Law Of Unintended Consequences we saw yet another study that looked at potential problems inherent in the massive distribution and consumption of antibiotics and antivirals during a pandemic.

 

WWTPs (Wastewater Treatment Plants) depend upon microbial activity in order to breakdown or `digest’ sewage.

 

Antibiotics in the sewage – at elevated levels such as might be seen during a pandemic – could inhibit microbial activity, resulting in the failure of WWTPs and the discharge of under-treated wastewater into the environment.

 

Today, a new study, this time on MRSA (methicillin-resistant Staphylococcus aureus) and how it fares in the wastewater treatment process. As many WWTPs provide reclaimed water for irrigation use, the concern is that MRSA shed in feces might make it through the plant and into the environment.

 

The University of Maryland-led study study appears as an open access article that appears in Environmental Health Perspectives. 

Methicillin-Resistant Staphylococcus aureus (MRSA) Detected at Four U.S. Wastewater Treatment Plants

November 1, 2012 Research 

Rachel E. Rosenberg Goldstein, Shirley A. Micallef, Shawn G. Gibbs, Johnnie A. Davis, Xin He, Ashish George, Lara M. Kleinfelter, Nicole A. Schreiber, Sampa Mukherjee, Amir Sapkota, Sam W. Joseph, and Amy R. Sapkota

Abstract

Background: The incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is increasing in the United States, and it is possible that municipal waste­water could be a reservoir of this micro­organism. To date, no U.S. studies have evaluated the occurrence of MRSA in waste­water.

 

Objective: We examined the occurrence of MRSA and methicillin-susceptible S. aureus (MSSA) at U.S. waste­water treatment plants.

 

Methods: We collected waste­water samples from two Mid-Atlantic and two Midwest waste­water treatment plants between October 2009 and October 2010. Samples were analyzed for MRSA and MSSA using membrane filtration. Isolates were confirmed using biochemical tests and PCR (polymerase chain reaction). Antimicrobial susceptibility testing was performed by Sensititre® micro­broth dilution. Staphylococcal cassette chromosome mec (SCCmec) typing, Panton-Valentine leucocidin (PVL) screening, and pulsed field gel electrophoresis (PFGE) were performed to further characterize the strains. Data were analyzed by two-sample proportion tests and analysis of variance.

 

Results: We detected MRSA (n = 240) and MSSA (n = 119) in 22 of 44 (50%) and 24 of 44 (55%) waste­water samples, respectively. The odds of samples being MRSA-positive decreased as treatment progressed: 10 of 12 (83%) influent samples were MRSA-positive, while only one of 12 (8%) effluent samples was MRSA-positive. Ninety-three percent and 29% of unique MRSA and MSSA isolates, respectively, were multi­drug resistant. SCCmec types II and IV, the pvl gene, and USA types 100, 300, and 700 (PFGE strain types commonly found in the United States) were identified among the MRSA isolates.

 

Conclusions: Our findings raise potential public health concerns for waste­water treatment plant workers and individuals exposed to reclaimed waste­water. Because of increasing use of reclaimed waste­water, further study is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated waste­water.

 

Environ Health Perspect 120:1551–1558 (2012). http://dx.doi.org/10.1289/ehp.1205436 [Online 6 September 2012]

Full PDF FILE

 

 

The full report runs 8 pages, and can be download here.

A summation of this research is available from the University of Maryland’s School of Public Health. I’ve cut to the chase with the excerpts  posted below, so follow the link to read the full story.

 

The School of Public Health News

November 5, 2012
NEWS RELEASE
Contact: Kelly Blake, kellyb@umd.edu, 301-405-9418

Superbug MRSA Identified in U.S. Wastewater Treatment Plants

University of Maryland-led study is first to document environmental source of the antibiotic-resistant bacteria in the United States

<SNIP>

They found that MRSA, as well as a related pathogen, methicillin-susceptible Staphylococcus aureus (MSSA),were present at all four WWTPs, with MRSA in half of all samples and MSSA in 55 percent.MRSA was present in 83 percent of the influent-- the raw sewage--at all plants, butthe percentage of MRSA- and MSSA-positive samples decreased as treatment progressed. Only one WWTP had the bacteria in the treated water leaving the plant, and this was at a plant that does not regularly use chlorination, a tertiary step in wastewater treatment.

 

Ninety-three percent of the MRSA strains that were isolated from the wastewater and 29 percent of MSSA strains were resistant to two or more classes of antibiotics, including several that the U.S. Food and Drug Administration has specifically approved for treating MRSA infections. At two WWTPs, MRSA strains showed resistance to more antibiotics and greater prevalence of a gene associated with virulence at subsequent treatment stages, until tertiary chlorination treatment appeared to eliminate all MRSA. This suggests that while WWTPs effectively reduce MRSA and MSSA from influent to effluent, they may select for increased antibiotic resistance and virulence, particularly at those facilities that do not employ tertiary treatment (via chlorination).

 

“Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater,” says Rachel Rosenberg Goldstein, environmental health doctoral student in the School of Public Health and the study’s first author. “Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater.”

(Continue . . . )

 

Most WWTPs are designed to efficiently remove solids and to disinfect discharge water, but do less well when it comes to removing chemicals.

 

Although only four plants were studied in this project, the results suggest that plants that fail to chlorinate routinely may be at greater risk of letting antibiotic resistant bacteria back into the environment. 

 

Whether it is antiviral or antibiotic metabolites, remnants from  illicit drug use, or resistant organisms themselves, what comes out of these treatment plants can affect our environment, and our population.

 

On a planet with 7 billion people, figuring out how to safely dispose of, recycle, or treat human waste has become a major challenge.

 

Shortcomings in WWTP systems – even seemingly small ones - can pose serious public health risks, including potentially creating and spreading resistant bacterial organisms.

 

As the authors of this study concluded, more research is now needed to evaluate and quantify the risk.

Pandemics & The Law Of Unintended Consequences

 

 

 

# 5348

 

A variation today on a theme we’ve touched on before.

 

What happens to the environment during a pandemic when large numbers of people in a community are taking – and subsequently excreting in their urine & feces – antivirals and antibiotics?

 

Many of the life-saving drugs used during a pandemic are excreted at some percentage from the human body unchanged or as a bioactive metabolite.  Tamiflu, Erythromycin, and Moxifloxacin are almost 100% bio-actively intact at excretion.

 

Supplemental Table 4. Assessing the Ecotoxicologic Hazards of a Pandemic Influenza Medical Response. Environ Health Perspect :-. doi:10.1289/ehp.1002757

 

 

A little more than four years ago, the subject of what happens to Tamiflu once it is excreted by the human body first graced these pages.

 

The blog was called The Law of Unintended Consequences, and it looked a study conducted at the Centre for Ecology and Hydrology in Oxford, England.

 

Their findings were released in the January 2007 issue of Environmental Health Perspectives (EHP) in a report entitled, Potential Risks Associated with the Proposed Widespread Use of Tamiflu, that illustrated what might happen if millions of people simultaneously began taking Tamiflu and releasing it into our environment.

 

The upshot of the the study was that scientists believed enough of the metabolite OC (oseltamivir carboxylate) would be present in some rivers and streams, after sewage plant processing, to present a genuine risk to the environment.

 

The concern being that enough Tamiflu might persist after wastewater treatment and release to rivers and streams that it might speed the development of resistant influenza viruses in waterfowl.

 

Fast forward to October of 2009 and we saw another report (see Everything Old Is News Again), based on studies done the previous year in Kyoto, Japan – that showed elevated levels of the OC Metabolite in wastewater discharge. 

 

More recently, investigators looking at the levels chemicals in rivers downstream from a pharmaceutical manufacturing hub in India, found staggering amounts of antibiotics along with signs of resistant bacteria. 

That story was recently well covered by Maryn McKenna on her Superbug Blog (see Drug residues and drug resistance in water: Not good).

 

Today, a new study appears in Environmental Health Perspectives that reports on another potential problem inherent in the massive distribution and consumption of antibiotics and antivirals during a pandemic.

 

WWTPs (Wastewater Treatment Plants) depend upon microbial activity in order to breakdown or `digest’ sewage.

 

Antibiotics in the sewage – at elevated levels such as might be seen during a pandemic – could inhibit microbial activity, resulting in the failure of WWTPs and the discharge of under-treated wastewater into the environment.

 

First a link to the study, an excerpt from the abstract, and a link to the press release . . . then I’ll return with a little more.

 

Assessing the Ecotoxicologic Hazards of a Pandemic Influenza Medical Response

Andrew C. Singer, Vittoria Colizza, Heike Schmitt, Johanna Andrews, Duygu Balcan, Wei E. Huang, Virginie D. J. Keller, Alessandro Vespignani, Richard J. Williams

Background: The global public health community has closely monitored the unfolding of the 2009 H1N1 influenza pandemic to best mitigate its impact on society. However, little attention has been given to the impact of this response on the environment.

 

Antivirals and antibiotics prescribed to treat influenza are excreted into wastewater in a biologically-active form, which presents a new and potentially significant ecotoxicologic challenge to microorganisms responsible for wastewater nutrient removal in wastewater treatment plants (WWPTs) and receiving rivers.

 

<SNIP>

 

Conclusions: The current pandemic influenza medical response might result in the discharge of insufficiently treated wastewater into receiving rivers, thereby increasing the risk of eutrophication and contamination of drinking water abstraction points. Widespread drugs in the environment could hasten the generation of drug resistance. These results highlight the need for empirical data on the effects of antibiotics and antiviral medications on WWTP and freshwater ecotoxicity.

Supplemental Material

(1.8 MB) PDF.

 

The 48-page supplemental file provides a pretty good look at the assumptions used in this computational study.

 

A press release summarizes this study’s findings, portions of which follow:

 

Centre for Ecology & Hydrology

Public release date: 2-Mar-2011

Effectiveness of wastewater treatment may be damaged during a severe flu pandemic

Existing plans for antiviral and antibiotic use during a severe influenza pandemic could reduce wastewater treatment efficiency prior to discharge into receiving rivers, resulting in water quality deterioration at drinking water abstraction points.

 

These conclusions are published this week (2 March 2011) in a new paper in the journal Environmental Health Perspectives, which reports on a study designed to assess the ecotoxicologic risks of a pandemic influenza medical response.

 

<SNIP>

 

The research team concluded that, consistent with expectations, a mild pandemic (as in 2009) was projected to exhibit a negligible ecotoxicologic hazard. However in a moderate and severe pandemic nearly all WWTPs (80-100%) were projected to exceed the threshold for microbial growth inhibition, potentially reducing the capacity of the plant to treat wastewater.

In addition, a proportion (5-40%) of the River Thames was similarly projected to exceed key thresholds for environmental toxicity, resulting in potential contamination and eutrophication at drinking water abstraction points.

(Continue . . . )

 

As Professor Emeritus of Statistics at the University of Wisconsin George E. P. Box famously observed:

 

“All models are wrong, but some models are useful.”

 

Until we actually see a severe pandemic combated by modern pharmaceuticals, it is impossible to know just how big the environmental impact will be. 

 

Computational models, such as the one above however, give us clues as to what might happen under various very specific scenarios.   

 

And what this study, and others in the past, have shown us is that the impact could be multi-faceted and pose significant public health ramifications.

 

The solution, of course, isn’t to withhold life saving antibiotics or antivirals during a pandemic. It is to recognize potential problems before they occur, and to devise contingency plans now on how to deal with them.

 

Much like the more famous Murphy’s law, the Law of Unintended Consequences is not a scientifically recognized law, as is Boyle’s or Torricelli’s.

 

Nevertheless, they can almost always be counted on introduce new complications anytime you attempt to to `fix something’.

 

Whether it is the creation of newly resistant organisms or the discharge of dangerous partially treated effluent into the environment, studies such as these give us new insight into unexpected problems we might face during a severe pandemic.