Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoe

Abstract

The objective of this study was to determine the incidence of Giardia lamblia acquisition in back-country travelers to a wilderness area, provide longitudinal follow-up on the incidence of symptomatic gastrointestinal illness and relate such information to concentrations of Giardia cysts in water samples from a high-use area. A prospective cohort non-interventional study of 41 healthy adult backcountry travelers from age 19 to 71 years in Desolation Wilderness, Lake Tahoe Basin was carried out. The incidence of Giardia cyst acquisition in backcountry travelers was only 5.7% (95% CI 0.17–20.2%). Mild, self-limiting gastrointestinal illness occurred in 16.7% of subjects (95% CI 4.9%–34.50%), none of whom demonstrated G. lamblia infection. Water sampling from three popular stream sites revealed cyst contamination to be generally at low levels with cyst concentrations in the single digit range for every 100 gallons filtered. G. lamblia contamination of water occurs, but at low levels. Acquisition of this parasite may be infrequent in backcountry recreationalists. Symptomatic gastrointestinal illness following wilderness travel can be due to other etiologies. Our findings may not be representative of all wilderness areas, but suggest that in the absence of documented G. lamblia infection, persons symptomatic following travel may suffer a self-limiting gastrointestinal illness. In such circumstances, empiric therapy for giardiasis is tempting but difficult to justify.

An Analysis of Wilderness Water in Kings Canyon, Sequoia, and Yosemite National Parks for Coliform and Pathologic Bacteria

“…Backcountry national park imal risk to humans. 6,7 In one study of Sierra Nevada water is used by summer backpackers, day hikers, fishbackpackers who developed diarrhea, none had Giarermen, and other recreational users. Precipitation that dia.…”

“…Precipitation that dia. 6 Although portable water filters may remove Giarcollects as snow during the winter storm season provides dia and other protozoal organisms, they easily become continuous water for streams into late summer from clogged with sediment and may be less useful on exsnow runoff. 1,2 tended trips.…”

“…The average concentration of less than 10 cysts/1000 L reported in studies of Sierra Nevada wilderness water poses minimal risk to humans. 6,7 In one study of Sierra Nevada backpackers who developed diarrhea, none had Giardia . 6 Although portable water filters may remove Giardia and other protozoal organisms, they easily become clogged with sediment and may be less useful on extended trips.…”

“…6,7 In one study of Sierra Nevada backpackers who developed diarrhea, none had Giardia . 6 Although portable water filters may remove Giardia and other protozoal organisms, they easily become clogged with sediment and may be less useful on extended trips. In addition, some water filters used by backpackers may be effective at filtering out Giardia but not bacteria.…”

Evidence-Based Medicine in the Wilderness: The Safety of Backcountry Water

“…The only prospective study examining individuals entering an area thought to have high levels of water contamination yielded no cases of symptomatic giardiasis. 7 Interestingly, some subjects in this study did develop diarrhea, but they did not have evidence of Giardia lamblia . This reminds us that infection is only 1 of the myriad causes of changing bowel habits during or after a trek.…”