CYST ACQUISITION RATE FOR GIARDIA-LAMBLIA IN BACKCOUNTRY TRAVELERS TODESOLATION WILDERNESS, LAKE TAHOE

The objective of this study was to determine the incidence of Giardia lamblia acquisition in backcountry travelers to a wilderness area, pro vide longitudinal follow-up on the incidence of symptomatic gastrointe stinal illness and relate such information to concentrations of Giardi a cysts in water samples from a high-use area. A prospective cohort no n-interventional study of 41 healthy adult backcountry travelers from age 19 to 71 years in Desolation Wilderness, Lake Tahoe Basin was carr ied out. The incidence of Giardia cyst acquisition in backcountry trav elers was only 5.7% (95% CI 0.17-20.2%). Mild, self-limiting gastroint estinal illness occurred in 16.7% of subjects (95% CI 4.9%-34.50%), no ne of whom demonstrated G. lamblia infection. Water sampling from thre e popular stream sites revealed cyst contamination to be generally at low levels with cyst concentrations in the single digit range for ever y 100 gallons filtered. G. lamblia contamination of water occurs, but at low levels. Acquisition of this parasite may be infrequent in backc ountry recreationalists. Symptomatic gastrointestinal illness followin g wilderness travel can be due to other etiologies. Our findings may n ot be representative of all wilderness areas, but suggest that in the absence of documented G. lamblia infection, persons symptomatic follow ing travel may suffer a self-limiting gastrointestinal illness. In suc h circumstances, empiric therapy for giardiasis is tempting but diffic ult to justify.