"Although limited, this study provides epidemiological evidence that submicron point-of-use water filters reduce the risk of waterborne cryptosporidiosis. Our findings further suggest that to substantially reduce the risk of waterborne cryptosporidiosis, users of submicron filters must avoid drinking untreated tap water both in and outside the home . . . "
American Journal of Tropical Medicine and Hygiene
So states the first field study to support what has long been known in the laboratory - Point of Use (POU) treatment can get the job done in reducing infections caused by cryptosporidium.
"Reduction of Risk of Watery Diarrhea With Point-of-Use Water Filters During a Massive Outbreak of Waterborne Cryptosporidium in Milwaukee, Wisconsin" was published in the American Journal of Tropical Medicine and Hygiene (1996) Vol. 56 No. 4. The study was conducted by leading epidemiologists and researchers David G. Aldiss and Dennis Juranic, Centers for Disease Control; Robert S. Pond, BASICS; Mark Remshak, Milwaukee Health Department; Susan Stokes, Scientific Resources Program and Jeffrey Davis, Wisconsin Division of Health. The researchers mailed a questionnaire to 155 individuals who had earlier responded to a Wisconsin Division of Health request for consumers to send in filter cartridges to help track the spread of the organism through the Milwaukee water system. Ninety-nine people filled out the questionnaire and formed the study group for the survey.
The study found that only 18 percent of the individuals who used a reverse osmosis or microfiltration system, and avoided tap water at home and work, became ill. Both of the individuals who became ill brushed their teeth with untreated water, and one drank tap water at a public building - indicating possible sources of infection unrelated to filtered water. Conversely, the rate of disease for those using submicron treatment systems, but who drank untreated water away from home, was 80 percent. For those using treatment systems greater than one micron, the illness rate was comparable to that of the general population.
While the study notes that boiling water is technically the most effective means of treating water infected with cryptosporidium, it also notes that individuals who drank microfiltered water during the outbreak, including water treated with reverse osmosis, were well protected. It went on to point out that filtering water is a more convenient alternative than boiling.
The nature of the study prevented its taking into account distillation technology, which has been extensively tested and proven effective for treating cryptosporidium. The study did not evaluate the effects of treated water on immune impaired individuals, the group considered to be most at risk for waterborne illness.
In related news, studies conducted by researchers at the University of Texas School of Public Health in Houston have shown an infection rate of 62 percent among volunteers exposed to as low a dose as 132 cryptosporidium oocysts. This is a low level, by biological standards, where as many as ten million cholera-causing bacteria may be required to infect a healthy adult; and points to the need for a high degree of absolute filtration or inactivation for effective water treatment.
As with any water treatment concern where health is an issue, WQA recommends that only units substantiated as absolute one micron filters, or those successfully tested for the reduction of cryptosporidium, be used for this purpose.
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