Follow by Email

Thursday, December 15, 2011

Giardia, The Most Common Pool Parasite is Not Your Neighbor

Giardia is a recreational water illness and is the most commonly found parasite in swimming pool water. This parasite can cause an intestinal illness in humans. It is possible to be infected even in a properly treated pool if the parasite is ingested before it has had adequate time to be killed. Casual contact of pool water into the mouth can ingest Giardia.

Although most bacteria are treated with recommended chlorine levels parasites like giardia are 15,000 times more resistant.

Giardia can be introduced into the pool water by fecal matter from infected animals or humans. It can take up to ten days for symptoms to occur after ingestion. Symptoms can be diarrhea, weight loss, fatigue, gas and bloating. It is highly recommended that people that have had diarrhea recently not use a swimming pool so that contamination cannot occur. However this advice of unhealthy pool behavior is not always followed placing other swimmers at risk. Persons with weakened immune systems and young children are at a greater risk of serious illness if infected with Giardia.


To determine if a swimming pool has Giardia you must take a water sample to a state or private testing lab. Testing for the presence of particular bacteria is not easily done by the pool operator so there are guidelines to be followed if a fecal accident occurs. If there has been a fecal accident in the swimming pool it should be treated properly according to guidelines set by the local bather code or the CDC. You must first determine if the fecal incident is a hard stool or loose stool as with diarrhea. Diarrhea usually occurs with a more virulent strain of bacteria so treatment for loose stools is much more stringent for chlorine level and concentration time of the chlorine to kill the possible bacteria.

Many of the pathogenic microbes are removed by swimming pool and spa filters but sand filters do not filter to a low enough micron to remove any of them.  DE filters and cartridge filters do the best job of removing microbes from the water.

Formed stools can act as a container for germs and removing them from the pool without breaking the stool apart can decrease the amount of bacteria released into the pool. In contrast a loose stool is more likely to contain bacteria and release them into the pool. Be sure to treat the stool removal tools so re-infection does not occur. It is not recommended to vacuum the stool from the pool.

If any type of fecal accident does occur you must first have all the swimmers leave the pool. This includes any pool that is on the same filtration system. If they are separate bodies of water but share the filtration system all bodies of water must be cleared.

For both formed stools and diarrhea, remove as much of the fecal matter as possible using a net or scoop device. Dispose of this matter into a plastic bag and use a trash container outside of pool facility to dispose in. Sanitize the net or scoop. You can place the net or scoop into the pool water while it is being treated.

We use a CT value which is the concentration time of free available chlorine in part per million (ppm) multiplied by the time in minutes. The CT value for Giardia is 45. Therefore if we take 45 and divide by 4ppm it would take 12 minutes to treat the pool with 4ppm of free chlorine.

For formed stools, raise the free chlorine level to 2ppm and adjust the pH between 7.2 – 7.5. The pH level is very important as it determines how active the chlorine will be. Maintain a free chlorine level of 2ppm for 30 minutes with the pool closed. 2ppm must be maintained until the end of the 30 minutes. Check with your local codes to see if they require any other times or chlorine levels. If there is a presence of chlorine stabilizers, a higher chlorine concentration may be required. Also increasing the chlorine level can decrease the amount of time for the pool closure or concentration time of the chlorine by using the before mentioned formula for CT value.

For diarrhea or loose stools we want to raise the free chlorine level to 20ppm and maintain the pH between 7.2 – 7.5. This will ensure treatment for more chlorine resistant bacteria if present. One of the most chlorine resistant bacteria is Cryptosporidium. Cryptosporidium has a CT value of 9600 and a free chlorine residual of 20ppm must be maintained for 8 hours to treat the pool.

The pool filtration system needs to be running during the treatment time. With diarrhea treatment the filter system needs to be backwashed or have the media changed if filter type requires such operation after treatment. Do not return the backwash water into the pool.

Swimmers can be allowed back into the pool once the CT value has been met and the chlorine level has been returned to normal operating range as allowed by state code.

If this is a public pool then a fecal accident documentation form should be recorded. This record should provide what type of stool it was and what treatment was taken as well as any other actions including disinfecting of equipment and filter cleaning. A log of the pool chemical parameters upon re-opening of the pool should also be noted.

Giardia and other harmful bacteria can be introduced to the pool at any time and the pool operator should always be knowledgeable and have the equipment to react quickly.
For more information:  CDC Giardia Prevention

1 comment:

  1. Heya¡­my very first comment on your site. ,I have been reading your blog for a while and thought I would completely pop in and drop a friendly note. . It is great stuff indeed. I also wanted to ask..is there a way to subscribe to your site via email?










    Removing Swimming Pool

    ReplyDelete