Forty-eight studies were included in the review: 3 cohort studies, 23 case-control studies and 22 cross-sectional studies. It was not possible to determine the number of patients included, as details were only given of the 33 with appropriate control groups (N=10,794). A further 4 studies that met the inclusion criteria were excluded because they were not published in English.
Of the 2 studies which had the highest validity, both were cross-sectional and both found increased risks of CDAD with antibiotic exposure. One (N=347) found an RR of 2.07 (95% confidence interval, CI: 1.06, 6.62) for cephalosporin exposure for up to 1 week and an RR of 3.62 (95% CI: 1.28, 8.42) for penicillin exposure of 1 to 2 weeks, adjusted for age and severity of disease. The other larger study (N=2,671) found an OR of 4.22 (95% CI: 2.11, 8.45) for clindamycin and an OR of 1.49 (95% CI: 1.23, 1.81) for increased numbers of antibiotics, adjusted for age, length of stay and proximity to patients with CDAD.
Forty-one of the 48 studies found an increased risk of CDAD associated with antibiotic exposure in hospitals. The overall ORs ranged from 2.86 to 6.92 in 33 studies with appropriate control groups. One cohort study recorded an RR of 2.48. The ORs for specific antibiotic ranged from 2.12 to 42 for clindamycin, and from 3.84 to 26 for third-generation cephalosporins.