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Thread: cdc guidelines for disinfection...

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    tgmb's Avatar
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    cdc guidelines for disinfection...

    Getting my pool log up to speed, and found this website- good stuff to know, especially about cryptosporidium....

    http://www.cdc.gov/healthywater/swimmin ... table.html

    What I find interesting, and disconcerting, is the whole cryptosporidium issue- am I correct in assuming that crypto can survive in a properly chlorinated pool?
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    Re: cdc guidelines for disinfection...

    You might notice that they have it at 1 ppm FC. That's when it takes a week and a half.

    If you run it up to high shock, it can be safe within a day http://www.cdc.gov/healthywater/pdf/swi ... ridium.pdf

    But yeah, it's tough to kill. It can pass right through your stomach unscathed.
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    Re: cdc guidelines for disinfection...

    Cryptosporidium isn't especially common in the environment. Pretty much the only place it comes from is infected people. Once it gets into the pool, it will die off after a while. Worst case it could be a few weeks, but it will eventually die off. Therefore, in a residential pool the only likely problem is person to person transmission when swimming with someone who already has it.

    If you know someone with cryptosporidium has been swimming, go to shock level for 24 hours.
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    Re: cdc guidelines for disinfection...

    Richard- Thanks. I printed that page out.

    Tom
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    Re: cdc guidelines for disinfection...

    Although this footnote is disconcerting...

    §Crypto CT inactivation values are based on killing 99.9% of Crypto. This level of Crypto inactivation cannot be reached in the presence of 50 ppm chlorine stabilizer, even after 24 hours at 40 ppm free chlorine, pH 6.5, and a temperature of 77°F (25°C). Extrapolation of these data suggest it would take approximately 30 hours to kill 99.9% of Crypto in the presence of 50 ppm or less cyanuric acid, 40 ppm free chlorine, pH 6.5, and a temperature of 77°F (25°C) or higher. Shields JM, Arrowood MJ, Hill VR, Beach MJ. The effect of cyanuric acid on the chlorine inactivation of Cryptosporidium parvum in 20 ppm free chlorine. J Water Health 2009; 7(1):109–114.
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    Re: cdc guidelines for disinfection...

    If you get Crypto in your pool from an infected person having a diarrhea incident, then it takes extraordinarily high levels of active chlorine to kill it off. It is true that having CYA in the water significantly lowers the active chlorine level. To get the equivalent of 10 ppm FC with no CYA, you would need to raise the FC to roughly around 10 ppm FC higher than the CYA level and that would be for a 25 hour kill time for a 99.9% kill, though you'd have to significantly lower your pH first (say, to 7.0) since the high added FC level will significantly raise the pH.

    In practice, you don't have to worry about this. I've never seen a Crypto incident reported from any residential pool in any pool forum ever. It is most commonly seen in some public pools where one infected person can infect dozens or others (or more). In most cases, the people know they are sick (though they don't know they specifically have Crypto) and have diarrhea and are being irresponsible swimming in a pool in the first place.

    An easier way to kill Crypto if introduced in a pool would be to use 1-2 ppm chlorine dioxide overnight for 8-10 hours. This can be created by adding sodium chlorite to a pool with a low level of chlorine, but the manufacturers never spent the $1-2 million for the efficacy and especially the expensive safety/toxicity studies to get this product approved for use in pools for this purpose.

    UV and ozone systems can kill Crypto that circulates through the system and are currently the primary approach used in public pools to control Crypto though it still won't prevent person-to-person transmission. It is mostly to kill it off so that it doesn't keep infecting people over the next days and weeks.
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    Re: cdc guidelines for disinfection...

    Yes, I would try not to make it a habit of inviting feverish diarrheal people over for swim parties....

    Tom


    "Symptoms
    By Mayo Clinic staff

    The first signs and symptoms usually appear two to seven days after infection with cryptosporidium and may include:

    Watery diarrhea
    Dehydration
    Weight loss
    Stomach cramps or pain
    Fever
    Nausea
    Vomiting
    Symptoms may last for up to two weeks, though they may come and go sporadically for up to a month, even in people with healthy immune systems. Some people with cryptosporidium infection may have no symptoms."
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    Re: cdc guidelines for disinfection...

    Thanks for this. I occasionally utilize local indoor pools for PT rehab, especially neuro patients. Some of the elderly have had bouts of c-diff during their hospital stay and they must be finished with their antibiotic treatment and w/o symptoms in order to enter the pool.
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    Re: cdc guidelines for disinfection...

    And C Diff is notoriously persistent as well, but as a fomite on above water surfaces. Any I.D. people or biology types care to speculate on the activity of resistant spore based organisms in pool water?
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    Re: cdc guidelines for disinfection...

    Quote Originally Posted by tgmb
    Yes, I would try not to make it a habit of inviting feverish diarrheal people over for swim parties....
    :
    Symptoms may last for up to two weeks, though they may come and go sporadically for up to a month, even in people with healthy immune systems. Some people with cryptosporidium infection may have no symptoms."
    If one has Crypto without symptoms and that includes not having diarrhea, then one is not as likely to be releasing oocysts into the water in great numbers (and they do not multiply in the water; they require hosts). Having the host get diarrhea is part of the normal life cycle for that organism -- it's the way to force oocysts into a watery environment to find another host.

    Again, not a single report of Crypto in residential pools. In this report, at the end of the swim season samples were taken from 160 public swimming pools in Atlanta, GA, 6.2% tested positive for Giardia intestinalis while 1.2% test positive for Cryptosporidium spp.. Crypto is the leading cause of intestinal illness from public pools because it is very chlorine-resistant. In pools improperly treated with chlorine (i.e. with very low or zero FC levels), many other pathogens can cause illness so while chlorine has significantly lowered the total illness rate, what is leftover is mostly from Crypto.

    I noted Giardia lamblia (intestinalis) which is also a protozoan cyst in pool water but though chlorine resistant, it is not nearly as resistant as Crypto. Clostridium difficile is different in that it is not a protozoa and is an anaerobic bacteria, but it does go through a spore stage and is shed through feces. The CT value for 3-log reduction (99.9%) for Crypto oocysts is 15,300 while for Giardia cysts it is 45 and for Clostridium spores it is about 45,000 (based on Rutala, 2006 showing 4-log reduction in 10-20 min. with 6000 ppm hypochlorite). So Clostridium in pools would be even more resistant to chlorine than Cryptosporidium, but I couldn't find info on the number of spores needed for infection, but as described in this link, C. difficile can be found in the stools of over half of children under 2 years old and of 5% of healthy adults. Healthy people rarely develop symptoms of C. difficile infection because other bacteria normally present in the intestine prevent C. difficile germs from multiplying.
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    Re: cdc guidelines for disinfection...

    I was told that the primary means of removing cryptosporidium in public pools is coagulation and filtration.

    I haven't heard much talk about coagulation on TFP... but I guess that's because its a forum for residential pool owners.
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    Re: cdc guidelines for disinfection...

    That would make sense; most c Diff. infections involve immunocompromised patients with depleted normal flora; not your typical poolgoer...
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    Re: cdc guidelines for disinfection...

    Quote Originally Posted by tgmb
    Yes, I would try not to make it a habit of inviting feverish diarrheal people over for swim parties....

    Tom
    ROFL, good policy. I think I'll have to add that to my Pool Rules sign. "NO feverish diarrheal people in the pool"
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    Re: cdc guidelines for disinfection...

    No doubt they'd sue- F.D.P.s have rights too, you know...
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    Re: cdc guidelines for disinfection...

    Quote Originally Posted by loop_pea
    I was told that the primary means of removing cryptosporidium in public pools is coagulation and filtration.
    Europe tends to focus more on coagulation/filtration in general for commercial/public pools as that is part of the German DIN 19643 standard. 19643-1 defines general requirements, 19643-2 is the base standard using GAC adsorption, flocculation, filtration and chlorination, 19643-3 adds ozone and 19643-4 adds ultrafiltration. Such coagulation/filtration is primarily used to reduce organics that would otherwise be precursors to disinfection by-products, but it also can help remove protozoan oocysts and spores as well.

    In the U.S., there seems to be little focus on coagulation/filtration and instead the CDC has a Fecal Incident Response Recommendations for Pool Staff that uses super-chlorination. In practice, DE and "dirty" high-rate sand filters may capture Crypto (or in some cases with sand, break open cysts and then chlorine kills the protozoa inside).
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    Re: cdc guidelines for disinfection...

    Quote Originally Posted by Puffin
    Quote Originally Posted by tgmb
    Yes, I would try not to make it a habit of inviting feverish diarrheal people over for swim parties....

    Tom
    ROFL, good policy. I think I'll have to add that to my Pool Rules sign. "NO feverish diarrheal people in the pool"

    Funny stuff here. I spit my drink on the keyboard after reading both comments. Awesome.
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    Re: cdc guidelines for disinfection...

    Interesting article here on chlorine dioxide, TCDO and HydroXan.

    SeaKlear claims their PRS product traps crypto, here

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    Re: cdc guidelines for disinfection...

    I stumbled upon the Model Aquatic Health Code (MAHC) earlier today (a total accident), and this is what it says about dealing with cryptosporidium:

    In pool water that contains chlorine stabilizer such as cyanuric acid, the pH shall be lowered to 6.5 and the free chlorine residual shall be raised to 40 mg/L and maintained for at least 30 hours or an equivalent CT value as shown in the Annex.
    6.5 eek!

    It might kill the crypto, but what else will it do to your pool?

    Daft logic for using these numbers too - they just happen to be some numbers used in one particular experiment on determining CT values.
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    Re: cdc guidelines for disinfection...

    I commented on MAHC initially during the public comment period at the end of December, 2008 and then again with later modules at the end of September, 2010. The module you are referring to is 6.5 Fecal/Vomit/Blood Contamination Response Code – Draft 10/01/2008 for Public Comment and the details are in 6.5 Fecal/Vomit/Blood Contamination Response Annex– Draft 10/01/2008 for Public Comment where I excerpt the relevant section below:

    Chlorine stabilizers such as cyanuric acid slow disinfection; therefore, higher chlorine levels may be necessary to reach the CT value for Crypto inactivation in pools using chlorine stabilizers. Limited data suggest that a 3-log inactivation of Cryptosporidium is possible in more extreme conditions when 50 ppm cyanuric acid was present in the water (pH of 6.5, free chlorine residual of 40 mg/L) (Shields JM, Arrowood MJ, Hill VR, Beach MJ. The effect of cyanuric acid on the chlorine inactivation of Cryptosporidium parvum. J Water Health 2008; in press). The level of cyanurate mentioned above (i.e., 50 ppm) was the concentration used in the experiment and should not be construed with suggested operating conditions; pool operators should not add additional cyanurate to a pool to reach 50 ppm. Higher levels of stabilization (i.e., >50 ppm) are not known to decrease disinfection efficacy further.
    At a pH of 6.5 with 40 ppm FC and 50 ppm CYA, the active chlorine level is 2.4 ppm which is equivalent to 4.9 ppm FC with no CYA at a pH of 7.5. If this is maintained for 30 hours, then this is equivalent to a CT of 8820. That is less than the 15,300 CT for Crypto but can be readily explained by the chlorinated isocyanurates having some oxidation capability which at 1/100th would add the equivalent of 2*40/100 = 0.8 so 5.7 ppm FC to bring us to a CT of 10,260. The rest of the error is likely variation in experimental results as well as inaccuracy in measured CYA level since the active chlorine level is VERY sensitive to the precise FC and CYA levels when the FC gets close to the CYA level. For example, at a pH of 6.5, 40 ppm FC at 40 ppm CYA has an active chlorine level of 4.5 ppm equivalent to 9.2 ppm FC with no CYA at pH 7.5 and would exceed the 15,300 CT.

    I told the CDC that if the FC is raised to around 10 ppm FC higher than the CYA level, then that would meet the required 15,300 CT requirement at a pH of 7.5, but that the pH would have to be significantly lowered first when adding hypochlorite sources of chlorine. For example, if one starts with pH 7.5, TA 100, FC 5.0, CYA 50, then if one first lowers the pH to 6.6 using acid and then adds 55 ppm FC using a hypochlorite source of chlorine, one ends up with pH 7.5, TA 107, FC 60, CYA 50 for an active chlorine level of 6.2 ppm equivalent to 12.6 ppm FC with no CYA at pH 7.5 so would be needed to be maintained for about 20 hours.

    Basically, using chlorine to kill Crypto doesn't make a lot of sense. Using coagulation/filtration makes more sense and in cases where a fecal incident occurs it would be far easier to simply use 1-2 ppm chlorine dioxide overnight since it has a much lower CT value against Crypto (reports vary, but the higher ranges are CT of around 400 for 3-log inactivation. Regarding chlorine dioxide (including TCDO and HydroXan that CaOCl2 mentioned, it can only be effectively used in indoor pools because chlorine dioxide breaks down in sunlight and does not combine with CYA (though CYA's UV shielding effect may help somewhat).
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    Re: cdc guidelines for disinfection...

    Thanks for the explanation chemgeek. I had read the advice as holding the pH at 6.5 during the superchlorination process, and thought that might not be very kind to plaster/tile grout etc. In real life, you wouldn't be able to do that. You'd lower the pH to 6.5 first, but it would rise when adding all that calcium hypochlorite (you wouldn't be able to measure this due to the high chlorine and so it would pass unnoticed?).

    I find it odd that the CDC acknowledges the effect of cyanuric acid on kill times for nasty bugs like crypto, but not on your average everyday germ that finds it's way into a pool and needs to be killed in seconds, not 15 minutes.
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