TABLE 2.

Frequency of new C. difficile strains isolated on different culture occassions^a

Age of child	No. of children sampled	No. (%) of newly acquired strains	No. of new strains/wkb
1 wk	41	12 (20)	12
2 wks	41	1 (1.7)	1.0
4 wks	42	2 (3.4)	1.0
2 mos	41	7 (12)	1.8
6 mos	42	11 (19)	0.7
12 mos	41	25 (42)	1.0
18 mos	23	1 (1.7)	0.04
36 mos	17	0 (0)	0
Total	42	59

^aC. difficile was isolated by culture of fecal samples from 42 Swedish infants positive for C. difficile at least once in the first year of life.

^bNumber of new strains acquired per week since the previous sampling occasion. The calculation was based on the assumption that no strains that were acquired between two sampling occasions were lost before the second of the samplings.