使用膜过滤——免疫荧光分析程序，对太平洋西北部三条原始河流的水样进行了贾第鞭毛虫囊肿的存在和浓度分析。在九个月的时间里，从三条河流和12条支流的17个采样站每月或每两个月采集222个样本。使用在0.5到50个囊肿/L范围内接种囊肿的样本监测囊肿恢复效率。通过26组样本，该程序的恢复效率平均为21.8%+6%。 在94例（42%）标本中发现了贾第虫囊肿。根据回收率和样本量计算的相应囊肿浓度范围为0.1至5.2个囊肿/L。阳性样本中囊肿浓度的分布为对数正态分布。在这三条河流中，囊肿浓度的大小（如平均值所示）和变异性（如分布斜率所示）都不同。没有发现统计上可支持的季节变化。主要结论是，即使在相对原始的河流中，贾第虫囊肿似乎也持续存在，尽管浓度较低。 包括12个参考文献、表格和图表。

Water samples from three pristine rivers in the Pacific Northwest were analyzed for Giardia cyst presence and concentration using a membrane-filtration --immunofluorescence-assay procedure. A total of 222 samples were collected either monthly or bimonthly over a ninemonth period from 17 sampling stations on three rivers and 12 tributaries. Cyst recovery efficiency was monitored using samples seeded with cysts at levels ranging from 0.5 to 50 cysts/L. The recovery efficiency of the procedure averaged 21.8 percent +6 percent through 26 sets of samples. Giardia cysts were found in 94 (42 percent) of the samples. The corresponding cyst concentrations calculated from the recovery efficiency and the sample volume ranged from 0.1 to 5.2 cysts/L. The distribution of cyst concentrations in positive samples was lognormal. Both the magnitude of cyst concentrations (as indicated by the mean value) and the variability (as indicated by the slope of the distributions) differed among the three rivers. No statistically supportable seasonal variations were found. The principal conclusion was that Giardia cysts appear to be continuously present, though at low concentrations, even in relatively pristine rivers. Includes 12 references, tables, figures.