"*It should be noted that a SteriPen does not "kill" anything – it sterilizes. All the little bad guys in the water are still going to be in the water, and thus make it into your body. However, they will be neutered and unable to make little bad guys."
John, I appreciate your excellent post about the differences between the Sawyer filters and steripens, and I just wanted to mention one little bit of trivia about your statement (above) about irradiation that doesn't have any bearing on the good general points you made in your post.
There are technical differences in the ways that UV irradiation affects bacteria, protozoa, and viruses, but it does kill them (except viruses, which are not alive).
Bacteria are essentially transparent (some have pigmented bits), so all of their DNA is vulnerable to UV damage, not just the DNA that controls reproduction. By dimerizing pyrimidine bases, the UV from a steripen renders bacteria unable to produce the proteins they need for basic functions (not just reproduction), and those bacteria really die.
Protozoan cysts and oocysts (like Giardia and Crypto) are in a metabolically inactive state, and their immediate need to express proteins is minimal, so they don't immediately die. But the irradiation essentially "traps" them in their egg-like form and prevents any later activity (like excystation and infection of a host) that would require protein expression. The irradiation does kill them, but they may take months or years to die, and they are crippled in the meantime.
Viruses are not "killed" by steripen irradiation because they are not alive. They are non-living protein machines that do not use energy or grow. It does destroy their DNA (or RNA in the case of Norovirus) and make them unable to cause illness. Some viruses might still be able to get into your cells, but the viral DNA they deliver is harmless irradiated junk and your cells just recycle them.
Incidentally, there are two other major classes of waterborne pathogens that are almost never discussed by backpackers: helminths (worms) and amoebae. Tapeworms (like Echinococcus or Taenia), roundworms (like Ascaris, Baylisascaris, and Toxocara), and amoebae (Entamoeba) produce cysts that can be present in water near campgrounds or in backcountry water. These are more common in tropical areas, but tapeworm and roundworm eggs are spread by foxes, wolves, domestic dogs, raccoons, and livestock, and they are known in waters in the US (mostly in the western states and Alaska). Some of these can cause fatal infections in humans (eg, Echinococcus), although the number of reported infections in the US each year is small. Amoeba infections aquired by ingestion of contaminated water are not fatal (nasal inhalation of Naegleria is different) but waterborne amoebic dysentery occurs in the US. Like Giardia, the illness is not pleasant. Like Crypto and Giardia, the eggs of worms and amoebae are immediately inactivated and eventually die following steripen irradiation.
In summary, steripen irradiation has these effects on waterborne pathogens:
1. Bacteria (e.g., Campylobacter): inactivated immediately, killed rapidly
2. Protozoan cysts and oocysts (e.g., Giardia): inactivated immediately, killed slowly
3. Helminth eggs (e.g., Echinococcus): inactivated immediately, killed slowly
4. Amoebic cysts (e.g., Entamoeba): inactivated immediately, killed slowly
5. Viruses (e.g., Norovirus): inactivated immediately
As I said, this doesn't change anything about your post, just a minor correction that I hope will be of interest to some.
