The most notorious protozoan parasites are:
- Entamoeba histolytica, 10-20 um cysts, cause of “amoebic dysentery”.
- Giardia lamblia, 8-16 um cysts, cause of “giardiasis”.
- Cryptosporidium parvum, 4-7 um oocysts, cause of “cryptosporidiosis”.
These protozoan parasites are unusually efficient at causing infections—most bacteria and viruses require hundreds or thousands of them to evade the body’s defenses but consuming as few as one of two cysts or oocysts is likely to lead to illness. The illnesses they cause are generally just a few days of diarrhea, cramps, nausea, etc. for most healthy people, but individuals with AIDS or HIV, cancer patients on chemotherapy, organ transplant patients on immune system therapy, and many infants and the elderly are more susceptible to long-term, life-threatening disease. In some communities, it is estimated that as much as 25% of the population may belong to endangered groups. Therefore, the efficiency of the fine filtration used to remove them is of paramount importance.
There are no official point-of-use filtration standards, but public health officials have approved systems and products that demonstrate 3-log or 99.9% efficiency for filtration of either live cysts/oocysts or test particles with a diameter of 1 um (micro-meter, or micron). Also, NSF International, a third-party certifying agency, has produced a voluntary filtration performance standard (Standard 53: Drinking Water Treatment Units—Health Effects) which has been accepted by most public health officials. NSF Std. 53 requires demonstrating at least 99.95% reduction of live cysts/oocysts, or alternately, at least 99.95% of test particles in the 3-4 um size range. That is about half the size of Cryptosporidium oocysts, which are the smallest of these parasites.
Pentair Everpure® precoat carbon filters are efficient fine filters capable of removing these cysts/oocysts by mechanical means*. They have been tested and Certified by NSF International to ANSI/NSF Standards 42 and 53 for more than 99.9% reduction of particles 0.5 to 1.0 um in size in the general filtration test, and for more than 99.99% reduction of 3-4 um particles in the Cyst Reduction test. Therefore, concerned individuals and businesses may use their water after filtration through these filters, even in the face of a “boil water order” or other notification of the presence of cysts/oocysts, but only if it is confirmed that the water is believed to be potable in all other respects.
*See individual system specification sheets for performance claims and FIFRA registration information.
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