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Web Exclusive - October 2017

Avoiding Recreational Water Illness Outbreaks

By Terry Arko


Recreational water illnesses (RWIs) are always a hot topic of discussion toward the end of summer when higher bather loads at aquatic facilities are faced with filters working overtime to keep pool water clean and clear. Unfortunately, there are always outbreaks—some bigger than others. The more severe the occurrence, the more likely it is to make mainstream media.

Cryptosporidium (Crypto) outbreaks happen every year. Unfortunately, traditional water sanitizers are not enough to battle this parasite, as it is highly resistant to chlorine and can linger in a pool for up to a week. When bather loads are high, and swimmers are swallowing water in the pool, facility managers need to have systems in place to help prevent the introduction of Cryptosporidium cysts, as well as systems to remove cysts from the water. That said, to avoid an outbreak, a two-pronged approach should be implemented:

  1. Taking physical steps to prevent the introduction of cysts into pool water by bathers.
  2. Employing secondary systems to: a) trap and remove Crypto cysts before swimmers ingest pool water; and b) deactivate the pathogen cysts so they are rendered inert and harmless should they be ingested.

Steps to Avoid an Outbreak

First, aquatic facility managers should put a prevention plan in place to try to avoid pool contamination. Should this fail, a secondary sanitation system should be used to remove dangerous Crypto spores from the pool, assuming they will likely enter the water at some point.

In the fight against these stealthy germs, industry professionals use several approaches based on research, health department regulations and current Centers for Disease Control (CDC) recommendations.

One of the most effective tools to prevent the threat of RWIs is still good old-fashioned chlorine. Due to its proven ability to disinfect, chlorine started to become popular for pool use in the '20s. Eighty years later, Life magazine called the use of chlorine as a disinfectant in water "one of the most important inventions of the last 1,000 years." When chlorine sanitizer is used against contaminants in pool water, there are varying contact time (CT) values that exist depending on the type of pathogenic (disease-causing) micro-organism.

For example, Giardia has a CT value of 45 minutes at 1 part per million (ppm) of chlorine. This means Giardia protozoa is inactivated in 45 minutes of contact with pool water carrying a 1 ppm residual of chlorine. To put things into perspective, Crypto has a CT value at 1 ppm of 15,300 minutes or 10.6 days. Therefore, it can remain active for a week, if not longer, in a standard chlorinated pool.

Recent studies conducted by the Environmental Protection Agency (EPA) have shown the average adult bather swallows up to 29.5 mL (1 oz) of water when swimming. Children typically ingest twice as much. With the possibility of billions of chlorine-resistant Crypto cysts present in pool water, it is easy to see how swimmers can become infected. This is especially true in pools with high bather loads.

Due to the fact Crypto is extremely chlorine-resistant and ranges between four and six microns, it is difficult to deal with. The majority of aquatic facilities still use sand filters, which are only capable of filtering down to 25 microns. Many residential pools, however, have filters that use diatomaceous earth (D.E.) media, which can pick up particles under four microns. This may appear to be the solution, and some service professionals may think Crypto would not be a problem in a pool with a D.E. filtration system; however, studies have shown Crypto cysts have the ability to elongate and press through filtration media in a viable state.

Current preventive measures for Crypto range from ensuring swimmers shower to keeping sick bathers out of the water. However, these measures alone are not enough to keep an outbreak from happening.

Other Methods for Dealing With RWIs

Ozone is becoming popular as a possible backup means for eradicating waterborne pathogens. In fact, ozone kills bacteria and Crypto cysts 3,125 times faster than chlorine.

Ultraviolet light (UV) is another system that is quickly gaining in popularity. In fact, after an outbreak at a splash park in New York in 2005 the State of New York has mandated the use of UV on all public splash park facilities. However, high turbidity of the water can be a problem that could cause UV systems to become ineffective against Crypto. For this reason, health departments also regulate turbidity levels in public pools.

The biggest problem with many public facilities is they rely only on chlorine, and use sand filtration. Thus, to effectively deal with Crypto, expensive upgrades such as ozonators and UV units need to be installed, and many private and publicly funded aquatic facilities do not have the budget to make these upgrades.

Some health departments also recommend hyper-chlorination methods when dealing with the suspicion of Crypto in pools. This typically entails raising chlorine levels between 20 and 30 ppm for eight to 12 hours. This method may vary depending on local health regulations. In 2004, however, the CDC reported there was no conclusive evidence to prove complete eradication of Crypto using this recommended method.

In North America, the standard protocol for water quality maintenance (WQM) is premised on the assumption that appropriate filtration and residual halogen disinfection will inactivate all pathogens. Experts agree that moving beyond the basics will require revising the two-pillar approach that includes filtration and halogen, and adopting supplemental disinfection for water quality management in pools and spas.

The costs involved in preventing RWIs using ozone, UV and regenerative filters can create sticker shock for those aquatic facility managers who have budget constraints. As a result, it may prevent some smaller facilities from taking these additional measures.

Inline UV disinfection is recognized as an extremely effective and reliable method for deactivating pathogens in the water and reducing the bather's exposure to disinfection byproducts. Some public health authorities are already beginning to mandate supplemental inline UV disinfection. After the Crypto outbreaks in upstate New York, New York State now mandates supplemental inline UV disinfection on all public splash parks as do several other states and provinces, such as Florida, Ontario and others.

Regular dilution of water is another means of reducing the risk of RWIs. This is already practiced by public pool facilities in Europe where there are requirements for an entire pool being diluted with fresh water over a month's time. Some other standards suggest adding 30 L (8 gal) of fresh water per day for every bather in the pool. This is obviously not viable in most areas of North America, especially those where regular droughts occur throughout the summer months.

In some areas, chemically laden pool water cannot be put to waste as it goes directly through the aquifers and could contaminate the groundwater. UV-treated water usually has drastically reduced sanitizer levels and, as a result, can safely be drained.