Giardia. Cryptosporidium. E. coli. These organisms spell potential disaster to the seasoned adventurer, who would never dunk his Nalgene into a river for fear of encountering them. But that same backwoods veteran might shrug off the risk of viruses, which, according to popular wisdom, aren't often encountered in North American stream water.
That's plain foolhardy, according to Wilderness Medicine Institute director Buck Tilton. "Treat water for viruses everywhere," he orders. He's not paranoid, notes Kellogg Schwab, an assistant professor at the Johns Hopkins School of Hygiene and Public Health. Schwab says Norwalk-Like viruses, a family of often waterborne pathogens, is responsible for an estimated 23 million cases of short-term diarrhea, nausea, and vomiting in the United States each year.
Such misery played through the minds of the virus-savvy back in January, when Seattle-based Cascade Designs announced it was pulling from stores all purifiers containing its ViralGuard cartridge. While a water filter traps bacteria and other microorganisms, a purifier typically uses a disinfectant—in Cascade's case, iodine beads—to kill the much smaller viruses that could otherwise slip through. But for reasons that remain unclear—Cascade inherited the purifier from SweetWater, a firm it acquired in January 1998—the ViralGuard failed Cascade's own quality-control tests. "We started seeing that [it] wasn't performing...in certain conditions," says company microbiologist Lisa Lange. Cascade stopped short of a formal recall and opted instead to remove the product from the shelves and release a bulletin alerting consumers to the trouble (so far, the company says it has received no reports of illnesses from ViralGuard owners). Owners of the two other iodine-based purifiers on the market needn't panic: Both Pur and Exstream claim their units use stronger doses of iodine than Cascade's. If you own a ViralGuard, or use a filter rather than a purifier, Cascade suggests you pretreat water with fresh household bleach: Three drops per liter (six if the water's cloudy, cold, or tea-colored), wait five minutes, and filter.
Cascade's Lange hasn't yet decided which viricide will replace the ViralGuard, except to say it likely won't be iodine-based. She might follow the lead of purifier maker General Ecology and pursue an extremely small-pore filter to impede the viruses mechanically—though users would pay for such a setup with elbow grease.Another option, reverse osmosis—a system of forcing water through a very fine membrane (as opposed to a fiber-based filter)—is effective but expensive, and the required tiny pores of such a system could easily clog with sediment. And while ozone injection kills viruses, the smallest portable ozone device on the market fits neatly inside a 27-foot trailer.
That leaves one possible surprise disinfectant that is neither chemical nor mechanical: ultraviolet light. This summer, a Maine company called Hydro-Photon will release the Steri-Pen, a kind of UV swizzle stick powered by four AA batteries. Plunk it in a 12-ounce glass of water and a microcontroller zaps the H2O for about 40 seconds. Then drink up. The device reportedly puts out enough UV juice to kill viruses as well as all other swimming pathogens. Turbid water reduces its effectiveness, though, and with its limited 12-ounce capacity and $195 price tag, the company imagines it'll appeal more to international travelers than backpackers.
So where does that leave us? Well, to hear microbiologist Schwab tell it, up you-know-what creek. "Anywhere anyone is defecating in the woods, you're at risk for viruses," he warns. "There are a lot of areas out there where drinking the water isn't a problem, but you just don't know. And sometimes the price for not knowing can be painful."