The Norwalk Virus

In the summer of 2001 and 2002 a couple of hundred people were infected with the Norwalk Virus on the Colorado River. Later it was found that the source of the virus of the Bureau of Reclamation Sewage Treatment Plant at Glen Canyon Dam. The plant tested positive in the treated outflow! This is the same virus that infected hundreds of people on the giant cruise ships in the Caribbean and Inside Passage to Alaska.

Thanks to Sonya Johnson for the following explanation!

 

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Dusting off my Harrison's _Principles of Internal Medicine_, here's what it says about the Norwalk virus:

It is a single-stranded RNA enteric (GI) calicivirus. It is, of course, spread via the fecal-oral route, and according to this text, is responsible for 1/3 of all epidemics of non-bacterial gastroenteritis in developed countries. It is most common in adults and is acute and usually self-limited. Incubation is between 18-72 hours. Apparently, it is a relatively common source of waterborne epidemics in places like nursing homes, cruise ships, etc. Symptoms are unpleasant, though: abrupt onset of nausea and cramps followed by vomiting and/or diarrhea. A generalized crappy feeling (headache, myalgia and slight fever) is also present. The symptoms usually last 24-48 hours.

Interestingly, people do not develop prolonged immunity to it as with other viral infections. So, if you are unlucky enough to come down with it once, if re-exposed to it 2 yrs. later, you'll get sick again.

In general I think most filters are too coarse to filter out viruses. That is what I gather from reading up on water filters. From what I understand about them, they cannot claim to be a water *purifier* unless they kill/filter out viruses, which none do without the help of additional chemicals. Otherwise, if it just filters out bacteria and protozoa, it is a water *filter*. There is one company (and of course I can't remember which one now) that had an internal chemical filter that was designed to zap viruses as well, but I think that was pulled to be redesigned.

Bleach will kill just about anything, if given enough time and the proper concentration. Same with iodine. But, if you are treating water with a lot of sediment in it, you'll have to use more bleach (or iodine), as viruses and bacteria will cling to small particulate matter. That's also the reason you will want to add your iodine before your Gatorade; otherwise, the bad guys will just cling to the Gatorade and the iodine won't be as effective.

Sonya

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