NEHA
Recommendations for reducing Cryptosporidium infection risk in swimming pools
Hello everyone and welcome to the presentation "Recommendations for Reducing Cryptosporidium Infection Risk at Swimming Pools."To ask questions about this presentation, please join the presenter in the networking lounge at the designated time listed on the agenda.I would now like to introduce Dr. Laura Suppes, an assistant professor in the Environmental Public Health Program at the University of Wisconsin in Eau Claire.
Greetings everyone and thanks for attending my presentation.Like the introducer mentioned, I will be talking about recommendations for reducing cryptosporidium infection risk at swimming pools, specifically for environmental health specialists.So, my background, I have done extensive research on swimming pools and I've also worked inspecting swimming pools as a registered environmental health specialist.So, just going to give you all some ideas today for trying to help your swimming pools out in trying to reduce the risk of cryptosporidium outbreaks.
So, objectives for today, number one, we're going to talk about why there's a risk of cryptosporidium infection at swimming pools, and then we're going to explore some methods for reducing cryptosporidium infection risk on a broad scale.So I'm going to just talk about anything that could potentially reduce risk.And then I'm going to talk about the most feasible methods for you, environmental health specialists.So, some -- hopefully some useful tools that you can apply in your jobs to try to help your pool operators reduce the risk of outbreaks.
So, why is there a risk of cryptosporidium infection at swimming pools?Well, we'll talk a little bit about what exactly cryptosporidium is.So we know that cryptosporidium causes cryptosporidiosis, which is symptoms including vomiting, diarrhea, nausea, and then in immunocompromised populations it can even cause death.So, people -- pregnant women, people who are using immunosuppressant therapies, and even children and the elderly.So, unfortunately, children are one of our immunocompromised populations and they're also a high exposure group.So they swim in swimming pools a lot, and we really want to be protective of this population.
And, unfortunately, we do see quite a few outbreaks of cryptosporidium in treated recreational water venues.So, between 2011 and 2012, 50% of the outbreaks in treated recreational water venues were caused by cryptosporidium.So it definitely is a problem.And, unfortunately, we're seeing outbreaks in swimming pools for a few reasons.So, number one, because we use chlorine as our primary disinfectant in swimming pools and it doesn't do a good job of killing cryptosporidium, so it takes 20 parts per million chlorine, about 13 hours to inactivate cryptosporidiosis.So, obviously, that's a solution that we really need to look at.And also swimming is community bathing, so it's basically a -- a swimming pool is basically a big bathtub.And you never know what somebody might be sick with who's swimming next to you.It's difficult to control other people's behavior.
If somebody does have an accidental diarrheal release, they can excrete up to a billion oocysts in one diarrheal accident.And if somebody accidentally, or maybe intentionally, swallows swimming pool water next to them, it only takes ten of these parasites for somebody to ingest to become sick.So, billions of oocysts in one diarrheal release, it only takes ten for somebody to swallow to get sick, so a very low infectious dose.And even if somebody doesn't have symptoms, so if they're not experiencing diarrhea, but they have had cryptosporidiosis, they can actually excrete the oocysts up to 50 days after they've stopped having diarrhea.So this can become a problem for re-contaminating swimming pools.
And then swimmers perception, so there's a false sense of security that chlorine sterilizes everything.Some people just don't understand that there are these chlorine-resistant pathogens that could be present in our present, oftentimes in swimming pools.And then last, swimming pools are recirculating.So it's community bathing, it's a big bathtub, and we're not just draining and dumping the swimming pool every time.We're recirculating it through a filter.And if our filter is not adequately removing cryptosporidiosis, we're potentially reintroducing those pathogens back into our pool water.So, all of these problems combined are reasons why we see cryptosporidium outbreaks in swimming pools.
So, looking at our outbreaks of cryptosporidiosis, according to the CDC, from 1978 to 2012, the blue bars represent the number of outbreaks associated with cryptosporidium in the United States.So we have seen an increase in outbreaks.We do know it's a problem.We do know that there is a risk of developing cryptosporidiosis from swimming in swimming pools.So that risk has actually been quantified, and so that's what this table shows.
So, basically, what this table says is that there is a risk of developing cryptosporidium infection, and the risk differs for children and adults.So it's higher for children because they swallow more pool water than adults do.And we know that there is -- there will be 29 children out of 1,000 who swim and who have an annual risk of getting cryptosporidium infection.So, 29 out of 1,000 children will get sick with cryptosporidium in one year of swimming.22 out of 1,000 adults will get sick with cryptosporidium infection from swimming in treated recreational water venues.So, ideally, we want this to be a very low risk or just not a risk at all.And so what can we do to minimize or to reduce the risk of developing cryptosporidium infection in swimming pools?
Well, here are some just broad methods for doing that.So I'm going to focus on the reasons why cryptosporidium is so often in our swimming pools.So I mentioned that chlorine doesn't do a great job of killing cryptosporidium.So maybe we should consider using something different, so, some alternative disinfectants perhaps.That's a control that we're going to explore in this presentation.
And then because we know that bathers can excrete so many oocysts and there are certain behaviors, like people thinking that chlorine is a solve-all problem and that pool waters are sterile, maybe we just need to focus more on reducing the introduction or stopping the introduction of oocysts in swimming pools.We'll explore some controls associated with stopping introduction.
And then last, because we're recirculating our swimming pool water, we do filter our pool water, but the filtration methods we're using aren't very effective right now.So let's make some more effective filtration techniques.So we'll explore that a little bit in this presentation.
I'm going to start by talking about using some alternative disinfectants.So, at the recommended free chlorine levels by the Model Aquatic Health Code and many swimming pool codes throughout the country, that concentration of chlorine is not going to inactivate cryptosporidium in a timeframe that reduces somebody's risk.So we know that the chlorine inactivation time of cryptosporidium, the contact time is 15,300, which basically means at one part per million chlorine, which is not atypical in a swimming pool, it's going to take that chlorine ten days to achieve a three log reduction of cryptosporidium.One part per million, ten days to achieve a three log reduction of crypto.So, basically, if we just had that pool water sitting in the swimming pool and we weren't recirculating it, one part per million would not be killing that cryptosporidium.Anybody who accidentally swallowed that pool water could potentially get sick.So we really can't use it -- we can't use chlorine as a technique to kill cryptosporidium in the pool water body.
But we do know that if we increase the concentration of chlorine, we can inactivate cryptosporidium faster.So we do use chlorine as a resource for responding to fecal accidents.So we use hyper-chlorination when somebody has a diarrheal release in swimming pools.But, unfortunately, there are some problems associated with hyper-chlorination.I'm bringing this up because I want people to start thinking about some different solutions that we can apply in the future and really get away from these solutions that aren't working, because obviously there is a risk and it's because we're not properly controlling this problem.
So there is a problem with hyper-chlorination.Number one, you have to use a lot of chlorine, which can be expensive.So it's expensive because you're buying a lot of the chlorine product.And then for some swimming pools that are relying on user fees, that closure time can eat into that revenue of user fees.So if you're having to close your swimming pool for 13 hours, then you're not getting paying patrons.
So, in addition to hyper-chlorination being expensive, it can also be logistically a problem.And so if you're having to maintain 20 parts per million chlorine for 13 hours, number one, maybe you have to pay an employee overtime.So if that swimming pool is being hyper-chlorinated overnight, an employee is going to have to be checking the chlorine levels every half hour, making sure it's at 20 parts per million the entire time, and you're going to have to pay that person.And they're going to have to use a test kit that might not be capable of reading a 20-part-per-million chlorine concentration, or it might not be reliable.So, operators are going to have to know their test kit's capability.They're going to have to know that they have to dilute the pool water in order to get the 20-part-per-million reading, or that they have to use test strips to try to see that the chlorine concentration is adequate.And so is this reliable or do people actually know what they're doing?So there is sort of some issues with operator error there.
We also need to know if there was even a fecal incident.So, how often are parents reporting that their child had diarrhea in the swimming pool?Maybe they're embarrassed about it.Maybe they're not telling the lifeguard or the swimming pool staff.Or maybe it's an adult, so maybe they're embarrassed to say that they had a diarrheal accident in the swimming pool.So, how often are accidents actually reported?
And then there's this issue of cyanuric acid.So, hyper-chlorination, or just chorine in general, doesn't work well when there's a lot of cyanuric acid in our swimming pools.So we use cyanuric acid in our outdoor swimming pools to prevent UV light from degrading chlorine, so it's a good thing.But if we have too much of it, it can interfere with the efficacy of chlorine at inactivating pathogens.So we don't want too much of it.We want an ideal concentration.
So, some research has been done recently, in 2015, on how cyanuric acid influences hyper-chlorination's efficacy at killing cryptosporidium.And so these are some important things to consider when we're talking about the effectiveness of chlorine at killing crypto.So, basically, what this study looked at was the inactivation of cryptosporidium under some different pool water conditions.So we have a pool water without cyanuric acid, pool water with eight parts per million cyanuric acid, pool water with 50 parts per million cyanuric acid, and 100 parts per million cyanuric acid.And the chlorine concentration in this study remains the same, 20 parts per million across the board.And the pH and temperature was the same as well across the board, 7.5 pH and 77 degrees Fahrenheit.
But when we look at the inactivation times of cryptosporidium under these different conditions, we see a really significant impact as cyanuric acid increases.So, without cyanuric acid, 20 parts per million chlorine inactivates cryptosporidium in eight hours, a three log inactivation.So it does an okay job, so a relatively good amount of time, eight hours.But as soon as we bump up that cyanuric acid to eight parts per million, as soon as we add it our time increases to inactivate crypto from eight hours to 14 hours.So it's going to take 20 parts per million chlorine 14 hours to inactivate cryptosporidium with eight parts per million cyanuric acid.So that really shows the influence cyanuric acid has on chlorine.
And then if we bump up from eight parts per million cyanuric acid to 50, that time to inactivate cryptosporidium at 20 parts per million chlorine increases to 62 hours, so two-and-a-half days, and not even -- a three log reduction is not even achieved.So they only saw a one log reduction of cryptosporidium in that study.And then, at the Model Aquatic Health Code's upper limit of cyanuric acid, which is 100 parts per million, it takes 72 hours to inactivate cryptosporidium at 20 parts per million chlorine .8 logs.So, again, we're not even achieving that three log reduction.And so this study influenced the new CDC Fecal Incident Response Guidelines.And it's very important that pool operators understand and are following these guidelines.
So the new guidelines that the CDC recommends for responding to a fecal accident to kill cryptosporidium, a pool without cyanuric acid stays the same, 20 parts per million for 12.75 hours.But as soon as there's some cyanuric acid, so if you have up to 15 parts per million cyanuric acid, you have to maintain that 20 parts per million chlorine for 28 hours, very important.For pools that have over 15 parts per million cyanuric acid, those pools have to drain the pool to reduce the cyanuric acid because that's the only way that you can reduce it, and then hold that chlorine -- that 20 parts per million chlorine for 28 hours.So this just shows the complications associated with using chlorine to kill cryptosporidium.
So why don't we explore some alternative disinfectants?In the Model Aquatic Health Code, there are some approved alternative disinfectants.Bromine is one of them, and there are pros and cons associated with that in some of these other alternatives.So, the benefit of bromine is, like chlorine, is leaves a residual, so we have some bromine that's disinfecting in our pool water body.But, unfortunately, there aren't any published contact time values for bromine to kill cryptosporidium.So we have some calculations available and we can try to estimate the inactivation times of bromine against cryptosporidium, but there aren't any studies that have explored this and published CT values.So maybe we could use bromine in the future, but, right now, there's some uncertainty associated with it.
UV light and ozone are go-to secondary disinfectants.They're secondary disinfectants because they, unfortunately, don't leave a residual in the pool water body.So, ozone, a little bit of a residual, but not enough where we can rely on that as our only disinfectant.So these are secondary to a disinfectant that leaves a residual in swimming pools.But we do know that UV light and ozone inactivates cryptosporidium very, very quickly, and so that's a benefit.So we can definitely use these as a secondary disinfectant through our circulation system.
Copper or silver ions is another approved alternative disinfectant in the Model Aquatic Health Code.And this is beneficial because there's a residual, but just like bromine we don't have any published contact time values.And then chlorine dioxide is also an approved alternative disinfectant, but, unfortunately, it's only approved for use in emergency situations.So we can only use chlorine dioxide to remediate cryptosporidium or another water quality issue if swimmers are not in the swimming pool.But it's beneficial because, like UV and ozone, it inactivates crypto very quickly and it also leaves residual.So this is definitely something that's worth exploring in the future.All of these alternatives to chlorine, which we know is associated with quite a few problems relative to cryptosporidium.
Okay.So we just talked about alternative disinfectants.So what about stopping the introduction or reducing the introduction of oocysts?So can we actually stop people from introducing cryptosporidium?Probably not, but we can reduce the contamination by controlling the source.And for those of you who had environmental health education, you've seen this environmental health hierarchy of controls.So the hierarchy of controls just helps us organize which controls we want to apply first to last.So which are the most cost-effective, which are the easiest to implement, and which are going to benefit swimmers the most, to the least cost-effective and probably the ones that are most associated with human error.
So we always want to try to apply elimination first, or substation.We want to eliminate the hazard or substitute the hazard for something less hazardous.We can then, if those don't work, we can try administrative controls, like education.If that doesn't work, we can change our engineering around, maybe alter our filters a little bit.And if that doesn't work, then we always try personal protective equipment, which is always the last control in the hierarchy because people might wear their PPE incorrectly.So I'm bringing up this hierarchy of controls because it can help us think about which controls environmental health specialists should be applying first.
Okay.So I've organized the controls that I'm going to suggest based on these risk factors that are associated with introduction of oocysts into swimming pools.So we know swimming is equal to community bathing.So, maybe we can think about separating children and adults somehow, and just exposing the truth about swim diapers.So they don't work.A lot of people probably don't know that, so let's start talking about that more.We know that bathers can excrete a billon oocysts in one fecal release; probably very important for us to not allow them into the pool, maybe to make some better swim diapers because they don't work right now; to improve our reporting of fecal incidences; and maybe to enforce some bathroom breaks.