TABLE 3.

Levels of bacteriophages carrying the Stx 2 gene and infecting E. coli O157:H7 in sewage

Sample source	No. positive/total no. testeda in a water sample of:						MPN/1 ml (lower limit–upper limit)b
	10 ml	1 ml	0.2 ml	0.1 ml	0.02 ml	0.01 ml
Sewage plant 1	9/9	6/9	2/2	9/9	1/2	0/7	3.4 (1.7–7.0)
Sewage plant 2	2/2	2/2	1/1	2/2	0/1	0/2	21.3 (5.3–84.6)c

^aThe number of positive samples in nested PCR analyses compared to the total number of samples studied. 

^bMPN, most probable number. The confidence limit was 95%. 

^cThe number of samples was too low to be meaningful.