Table 2.

Intra-study risk of bias, according to MOOSE Guidelines for Meta-Analyses and Systematic Reviews of Observational Studies, and confounders identified in component studies.

Study, year	Study design	Study population clearly defined?	Clear definition of outcome and outcome assessment?	Important confounders and/prognostic factors identified?
Al-Tureihi, 200523	Case-control	Yes	Yes	Age, and antibiotic treatment
Aseeri et al, 200824	Case-control	Yes	Yes	Admission date, sex, age group, antibiotic use, patient location, and room type
Baxter et al, 200825	Case-control	Yes	Yes	Number of days spent in the hospital, ICU days, antibiotics
Barletta et al, 201326	Case-control	Yes	Yes	Prior hospital admission, intensive care unit admission, admission from a skilled nursing facility, immunosuppression, number of antibiotics received, PPI duration, and time to event
Beaulieu et al, 200727	Cohort	Yes	Yes	Age, gender, length of stay, comorbidities, APACHE score, NGT feeding, tracheal tube placement, H2RA, and antibiotics
Dalton et al, 200928	Cohort	Yes	Yes	Independent covariates (demographics characteristics such as age, gender, race -ethnicity), albumin and white blood cell count at the time of CDAD diagnosis, the Charlson co-morbidity score, prior admissions to Montefiore Medical Center within 180 days, and prior use of antibiotics and PPIs. ( last two were dichotomous)
Dubberke et al, 200729	Case-control	Yes	Yes	Comorbid conditions that will increase the risk of CDAD (age, admissions, antibiotics, CDAD pressure, albumin level, leukemia/lymphoma, mechanical ventilations, H2RA, and anti-motility agents)
Howell et al, 201030	Case-control	Yes	Yes	Age, antibiotics, and propensity score-based likelihood of receipt of acid suppression therapy
Jenkins et al, 201031	Case-control	Yes	Yes	Not specified
Kazakova et al, 200632	Case-control	Yes	Yes	Antibiotics, H2RA, length of stay, COPD, psychosis, and depression
Kim et al, 201033	Case-control	Yes	Yes	Age, serum albumin level, and NGT feeding
Linney et al, 201034	Case-control	Yes	Yes	Age, sex, discharge date and hospital unit, antibiotics, IBD, cancer, diabetes, NGT feeding, LOS, and previous residence
Loo et al, 200535	Case-control	Yes	Yes	age, sex, number of days at risk for C. difficile associated diarrhea, Charlson index, and the use of chemotherapy, PPI, histamine H2 blockers and enteral feeding
Manges et al, 201036	Case-control	Yes	Yes	Controlled for Bacteroidetes, and Firmicutes spp.
McFarland, 200737	Case-control	Yes	Yes	Not specified
Modena et al, 200538	Case-control	Yes	Yes	Antibiotic use and infections
Muto el al, 200539	Case-control	Yes	Yes	Age, diabetes, organ transplantation, H2RA, and antibiotics
Novack et al, 201440	Case-control	Yes	Yes	Adjusting to Charlson index
Pakyz et al, 201341	Case-control	Yes	Yes	Controlling by patient level covariates NO hospital level medication covariates
Shah et al, 200042	Case-control	Yes	Yes	Not specified
Stevens et al, 201143	Cohort	Yes	Yes	Comorbid conditions within 48 hours following admission: diabetes, respiratory illness, kidney disease, transplant, and cancer.
Yip et al, 200144	Case-control	Yes	Yes	Not specified
Wang et al, 201445	Cohort	Yes	Yes	Not specified