Will Getting Rid of Biofilm Get Rid of Crypto?

Biofilm

A couple of weeks ago I attended the World Aquatic Conference in Atlanta that focused on health and safety issues in aquatic recreation.  There were a few sessions on Cryptosporidium and pool contamination.

A long time ago I spend three months in rural Ivory Coast in Africa and saw the effects of parasites on health.  There it is a daily, widespread and often fatal problem.  Trying to eradicate the parasites is impossible, so most of the medical effort centered on treatment.  Luckily, we have very few parasitic diseases so general knowledge about parasite patterns of transmission and growth are widely known.

Parasites in Pools and Lakes

Cryptosporidium, or Crypto for short, can be a serious health problem from pools and lakes.  Giardia in lakes is a type of Crypto.  Both parasites set up home in the intestines of mammals and cause diarrhea with the accompanying dehydration.

Contrary to most people’s belief, these parasites do not proliferate or “grow” in the water – only inside mammal’s intestines.  They can live in the water for long periods of time waiting for an unsuspecting mammal, maybe you, to swallow the water.  Then they set up shop and start to divide causing intestinal disease.  Huge numbers of Cryptosporidium parasites can reside in every stool from an infected animal or human.  As few a 10 ingested organisms can cause serious disease.

So how does a Crypto outbreak occur?

First, an individual who has Crypto living in their intestines has an “accident” in the pool.  The feces deposit millions and sometimes billions of Crypto organisms in the water.  Once in the water they disperse and become dormant. Each crypto organism is bigger than a bacterium, but still very small.  They reside in every nook and cranny of the pool including the microscopic water channels in biofilm (see previous blogs).

How are they killed?

Our old friend chlorine kills Crypto just like it kills bacteria and they are removed from the water by filtration.  In most pools it takes a lot of chlorine a long time to kill all the crypto organisms so after an outbreak of documented Crypto diarrhea.  The pool must be closed for hyperchlorination for a time period determined by the health board.   This can mean closing the pool for days.  We have no effective test to determine the presence of Crypto in the water, so the amount of time for hyperchlorination is determined by laboratory studies.

Throughout the conference, I kept thinking about Crypto and biofilm.

I heard about long periods of hyperchlorination required to rid an infected pool of the parasites.  I saw elegant scientific studies that looked at different filtration methods in the laboratory only to find that the increased reduction of parasites demonstrated in the lab could never be replicated in a pool.

Testing a Theory

That made me think about biofilm and its effect on chlorine.  Maybe the reason that it takes a long time of hyperchlorination to kill most of the crypto organisms is that the biofilm absorbs so much of the chlorine that very, very high levels for a long time are needed?  Maybe the Crypto parasites “hide” in the microscopic channels of water in the biofilm so the chlorine can’t easily reach them and kill them?  If these hypotheses are true, then ridding the pool of biofilm could result in efficient removal and killing of the Crypto parasites.

On the way home from the conference, Vance Feigel and I designed experiments to test these thoughts.  When they are done we’ll share them in our blogs.

David Knighton, MD

This entry was posted on Wednesday, November 18th, 2009 at 4:16 pm and is filed under Biofilm, Water chemistry. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.