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By Rita Moyes
November 29, 2000
Bacteria that gather in the piping of whirlpool bathtubs are difficult to remove and can cause serious health problems.
Editor's Note: The footnotes denoted in this article are listed at the end under "References."
Recent reports of whirlpool-associated septicemia1, skin infections2, urinary tract infections3, pneumonia4, legionellosis and Pontiac fever5,6 have raised serious public health concerns about the risks associated with whirlpool bathtubs. To assess these risks, whirlpool bath water samples were aseptically collected from private homes and hotels from across the United States. This article deals with whirlpool bathtubs that are filled and drained after each use, as distinguished from recreational spas and hot tubs.
A typical whirlpool bathtub incorporates a system of inaccessible air and water piping7. When a bather fills the tub and activates the system, normal flora, dirt, sloughed skin, body fluids, bath oils and additives, fecal matter and soap scum circulate through the system and build up inside the piping as biofilm. Biofilm is abundant in nutrient containing aquatic environments, and due to physiological cooperation, they are inherently more resistant to various antimicrobial treatments and cleaning methods. Manufacturers recommend flushing the system with automatic dishwasher detergent, bleach, vinegar or baking soda8,9,10, but the effectiveness of those products is highly doubtful (Hendrickson, Connie M. Ph.D., personal communication).
Most systems permit dirty bath water to back-fill the air piping when the pump is turned off. Unlike the water circulation piping, the air piping will not admit fluid while the pump is operating. Even if industry-recommended cleaning agents were effective, they cannot reach the air piping, which makes the complete system uncleanable by any means7.
Although the tub is drained after use, it appears that the circulation system itself does not fully drain. The industry standards committee of the American National Standards Institute has adopted a standard that permits the typical circulation system to retain over 10 fluid ounces of dirty bath water when the bathtub is fully drained11. Stagnant bath water trapped inside a system already rich in biofilm provides an ideal environment for infectious bacteria to flourish.
These factors combine to expose the bather to pathogenic organisms. The hazardous effects are compounded by the fact that these organisms are delivered in aerosol form due to aeration of the water through jets.
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The Study
Table 1.
Whirlpool bath samples were collected from all over the United States from both private homes and hotels, and were subjected to bacterial analysis. Aseptic technique was used to collect both tap and tub samples into sterile 100-ml water collection containers12. One container of tap water was collected after the tap was allowed to run for 1-2 minutes and four containers of tub water were collected after a clean tub was filled and the jets were engaged for 2-3 minutes. Bacteriological examination of the water first involved nutrient agar pour plates of water dilutions to assess relative bacterial numbers. Secondly, 100-ml volumes of water were filtered through a membrane filter with a pore size of 0.45 um, and the filters were then placed on Eosin Methylene Blue (EMB) agar, Mannitol Salts agar (MSA), Pseudomonas F agar, Buffered Cysteine Yeast Extract (BCYE) agar and Sabaroud agar. All the plates were incubated for 24-28 hours at 37|C, except for EMB, which was incubated at 44|C. By elevating the incubation temperature to 44|C for this group, many of the non-enteric coliforms are eliminated.
Findings indicate that, as compared to tap water samples, the bacterial numbers were greatly increased in the whirlpool tub samples (253 cfu/ml vs. 3.08 x 10 to the 6th power cfu/ml, respectively, P <0.002)(See Table 1.) Normal (nonjetted) tub water samples were not significantly different from tap water samples. Additionally, all whirlpool tub samples yielded microbial growth, whereas 72% of the tap samples showed no growth under the experimental conditions used in this trial. No data correlating the number of viable organisms in water with the risk of acquiring infection is currently available. However, the analysis of 100-ml filtered samples yielded TNTC (too numerous to count, or >300 cfu) in 61% of the tub samples tested, indicating that the bacterial load for a 100-ml sample was fairly high in a majority of cases.
Observance of the plated filters yielded the results listed in Table 2. Growth on EMB was followed by the use of Enterotube II, a commercial testing system (Remel) for identification of gram negative rods belonging to the Family Enterobacteriaceae. Escherichia coli, Proteus mirabilis, Yersinia pseudotuberculosis, Shigella sp., Serratia sp. and Klebsiella sp. were among the organisms identified in this group. Gram positive cocci that formed yellow colonies on MSA followed by a positive rabbit plasma coagulase test confirmed the presence of S. aureus. Pseudomonas F agar and OxiFerm tubes (Remel) were used to identify the presence of various Pseudomonas species. Sabaroud Dextrose agar and colony morphology indicated the presence of fungi. Buffered charcoal yeast extract agar with PAV was used for enhanced growth of presumptive Legionella species. (Vancomycin inhibits gram positive organisms and polymyxin B inhibits many gram negative bacilli; Anisomycin suppresses yeast.) Legionella pneumophila produces green colonies and Legionella micdadei produces blue colonies.
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Conclusions
Table 2.
Association of infections with whirlpool tubs has been recognized for a number of years, but due to the increased popularity and the use in hydrotherapy13, the matter should be brought to public attention. A previous study has shown the colonization of whirlpool baths with P. aeruginosa regardless of "the type of whirlpool bath, its length of time in use, exclusion of residents with incontinence, infection or skin problems, type of disinfection or method and frequency of disinfectant used, and whether the bath was serviced regularly"14. The results of the Hollyoak study prompted the Public Health Laboratory Service Water Committee in the U.K. to further investigate the link between the use of whirlpool baths and infections so that health guidelines can be established. Likewise, the Dutch government has launched a plan to combat Legionnaire's Disease by implementing water safety measures after 242 cases of Legionnaire's Disease developed due to exposure to aerosolized bacteria from a whirlpool bath at the Westfriese Flower Exhibition in the Netherlands in February 199915.
Due to the presence of pathogenic and potentially pathogenic organisms, education of the public on the hazards of piped whirlpool bathtub use should become a priority. Immunocompromised and post-operative individuals should discontinue use, and all individuals should avoid submersion of the head and possible ingestion of the water. Another concern, particularly in the hospital setting, is that a whirlpool bath could act as a reservoir of antibiotic resistant microorganisms. New technology in design and the use of professional cleaning systems would be beneficial in reducing the risks associated with whirlpool tub microbial exposure.
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Acknowledgements
The technical assistance of Stephen Bell and Kim Orr was
greatly appreciated. I would also like to thank the National
Council for Whirlpool Bath Health and Safety for its assistance
in sample collection for the survey.
References
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