Measuring disease outbreaks
The CDC provides a survey of disease outbreaks in pools and spas every two years. The latest survey covers 2011-2012. During this two-year period, there were 69 outbreaks in treated water (i.e. not a lake or river). A summarized breakdown of which organisms caused the diseases, how many outbreaks there were for each organism, and how many people were ill as a result is shown in Table 1 on previous page.
One of the major sources of contamination in pools and spas/hot tubs is bathers. Two of the organisms in this table may come from the environment (Pseudomonas and Legionella), but the majority are from swimmers. That said, bather hygiene is extremely important in minimizing pool water contamination. Showering immediately before swimming will not only minimize the number of pathogens entering the water, but will also lower the chlorine demand in a pool and/or spa/hot tub, as well as minimize disinfection byproducts.
What is the dirt on bathers?
How much contamination could possibly come from swimmers? Charles Gerba, and other researchers, have asked this exact question and provided the following data. Gerba’s study estimates an average of 140 mg (0.14 g) of fecal material is contributed to the water by each swimmer. Keep in mind, however, this value can vary depending on the personal hygiene of the swimmer. That said, he estimates the range can be from a minimum of 0.1 mg (0.0001 g) for adults to a maximum of 10,000 mg (10 g) for a child.
This is one of the reasons why the CDC published its Share the Fun, Not the Germs leaflet for distribution to swimmers to educate them on how they play a huge part in keeping a pool clean and safe.
Contamination can be minimized if swimmers shower before swimming, refrain from urinating in the pool and wash their hands after using the washroom. However, some contamination in the pool is inevitable; therefore, it is extremely important that there is a residual of a PMRA/EPA-registered sanitizer in all parts of the pool at all times.
By law, sanitizers and disinfectants must be registered with the PMRA/EPA to ensure their safety and efficacy.
Why is a residual important?
It is important to keep a sanitizer residual in the pool to prevent bather-to-bather disease transmission. There are a variety of techniques that can be used to kill bacteria and viruses (e.g. ozone, ultraviolet [UV] light, sterilization with heat, etc.); however, in a pool, it is also important to have a sanitizing agent in the water with swimmers.
As ozone, UV, and other in-line treatment systems used to kill bacteria and viruses are separate from the pool, a person using a pool with such a treatment system could still become infected if the swimmer comes into contact with the contamination in the water before it reaches the treatment system. To combat this, some residual sanitizer should always be circulating in the water.
Not only does a residual sanitizer need to be kept where swimmers are present, but also maintained in parts of the pool where there are not many swimmers (e.g. at the bottom of a diving well). A residual sanitizer should also be maintained at night and during periods of closure when no one is in the pool.
The reason for this is bacteria such as Pseudomonas and Legionella can grow and reproduce in an unsanitized pool. These organisms can form a slimy layer called biofilm. It is very hard for sanitizers to get into a biofilm and kill organisms harbouring there, so even if a sanitizer residual is re-established, it may not be able to fully sanitize the pool.
