By Dr. Jeff Williams and Nathan Kenney
A report by the Centers for Disease Control and Prevention (CDC) earlier this year entitled “Microbes in Pool Filter Backwash,” stirred up mass media attention, creating a cloud over public perceptions of swimming pool safety just as the season was entering full swing. In particular, reminding bathers about personal hygiene as a component of public pool use is always a good thing; however, the report’s findings rapidly became sensationalized by content-hungry news channels.
Rather than focusing public attention to the behavioural changes the CDC strives to attain, the report, which comprises an unsurprising set of microbiological findings on a limited range of pool filter samples, was converted from what should have been a general news story into lurid coverage of “poop in pools everywhere.”
This is unfortunate because making a beneficial and wholesome activity such as swimming more attractive to the masses, and encouraging increased participation, is critical to the efforts of getting people off the couch and doing something healthful, yet delightful. Raising fears about recreational water illness (RWI) risks can be a setback to these efforts. Therefore, it is important to use data from studies such as these in a healthier perspective.
Interpreting the ‘high-tech’ findings and assessing the risk
For this study, CDC researchers collected 161 backwashed pool filter samples from a number of public swimming pools, and tested them for biological contaminants using DNA probes. For this procedure, filtered particulates ended up being highly concentrated in a small amount of backwash water, which was then analyzed using DNA ‘fingerprinting’ to detect whatever was trapped on the filter medium. Due to the extraordinary sensitivity of this procedure, many of the filters, which were performing properly, were sure enough found to have trapped bacteria to the extent that more than half of the samples showed evidence of the presence of Escherichia coli (E. coli), which is commonly used as an indicator of fecal contamination. Roughly the same proportion also contained ‘fingerprints’ of Pseudomonas aeruginosa (P. aeruginosa), a microbe that can be human-associated, sometimes causing disease, but which can occupy and multiply in a wide range of environmental niches.
Now, what these findings signify has to be framed by the limitations of the technology; DNA probes provide quick and sensitive ID analysis of samples for specific microbes, but the interpretation of the results is limited without using other types of microbiological tools to arrive at an assessment of RWI risks. For example, the DNA technology used in the study will provide a positive signal in the backwash water sample whether the microbe is alive and potentially infectious, or dead and harmless—in this instance most likely eradicated by the pool’s chlorine (Cl) sanitizer, which is doing its job, taking care of the inevitable microbial contamination as a result of the pool’s bather loads. It would have taken many more microbiological procedures to get a handle on whether the E. coli or P. aeruginosa fingerprints truly represented a RWI risk, thus signifying the sanitation/filtration systems were faulty or not properly maintained. These are the types of signals that should cause alarm; however, they are often discovered in the aftermath of disease outbreaks.
That said, there were no such outbreaks at the pools involved in the study, thus, the findings, which garnered widespread attention, were not indicators of wholesale failures of proper sanitation and hygiene, and the bacteria detected were not in the primary disease agent category (e.g. E. coli O157;H7). Therefore, all of the anxieties raised by the newspaper headlines were not necessarily in good cause. Safe pool management practices were clearly working.
Adopting good personal hygiene practices as a way to lessen the amount of contamination the pool’s sanitation/filtration system has to deal with is a fair proposition; however, it is yet to be determined whether showering before entering the pool would significantly reduce the rate at which ultra-sensitive DNA probing returns positive signals of human-related microbial material in filter backwashes. It is certainly a reasonable notion, but it will be a challenge to test experimentally.