TABLE 2.

Comparison of the sensitivity of epifluorescence microscopy, direct PCR, and nested PCR for detecting oocysts retained on membrane filters

Filter	No. of oocysts counted (FITC labeled/DAPI labeleda)	Sensitivityb as determined by:
		Direct PCR	Two-step nested PCR
F filtersc
F1	11/6	Negative	ND
F2	6/5	1+	4+
F3	4/0	1+	4+
F4	8/7	Negative	4+
F5	7/4	Negative	4+
F6	8/4	Negative	3+
F7	7/5	Negative	4+
F8	4/2	Negative	2+
F9	6/5	Negative	1+
F10	12/10	Negative	3+
F11	10/7	1+	4+
F12e	9/2	Negative	4+
FC filtersd
FC1	5/2	Negative	3+
FC2	9/2	Negative	4+
FC3	9/3	Negative	4+
FC4	4/1	Negative	4+
FC5	15/9	Negative	3+
FC6	2/1	1+	3+
FC7	13/10	1+	4+
FC8	7/2	Negative	3+
FC9	12/5	Negative	3+

^aDAPI labelling refers to oocysts containing one to four nuclei.

^bNegative, no PCR product detected on gel; 4+, PCR product yielding a strong band; 3+ and 2+, PCR product yielding medium-strength bands; 1+, PCR product yielding a weak band on the gel; ND, not done.

^cF filters, filters through which seeded mineral water A was passed.

^dFC filters, filter controls (filters onto which a known number of oocysts were deposited [see text]).

^eFiltration of 1 liter of RO water.