1. Frequency of Clostridium difficile transmission by asymptomatic carriers during hospital admission Study 1: Transmission by asymptomatically colonised long-term care facility (LTCF) residents during hospital admissions 6-mo, single-centre study in Veterans Affairs hospital (USA): –25 hospital-onset cases of C. difficile infection (CDI) –38 asymptomatic carriers, identified through active surveillance in affiliated LTCF (molecular typing: restriction endonuclease analysis; REA): Skin and/or environmental shedding (>26 colonies/perirectal swab) : 63% ≥1x transferred to hospital : 53% Linkage = presence of incident CDI case on ward concurrently with or ≤30 days after discharge of another incident case or asymptomatic carrier + identical REA group or type 1 Donskey CJ. IDWeek 2014 abs. 529 2 Galdys A. IDWeek 2014 abs. 1646 1 of 2 Data from oral presentation All potential transmissions from asymptomatic carriers: linked to 5 shedders, including 1 carrier linked to 4 CDI cases during 3 hospital admissions

2. Frequency of Clostridium difficile transmission by asymptomatic carriers during hospital admission Study 2: Transmission by asymptomatic inpatient CD carriers 5-mo, single-hospital study (USA; 2013): N=515 pts undergoing active surveillance testing (AST) for CD via perirectal sampling during 5-day period –57 (11%) inpatient CD carriers (positive AST without clinical CDI during 3 mo before or after AST) ; 65% harboured toxigenic CD strains –123 clinical CDI cases, identified during 7 wk prior to AST, 5-day AST period, or 12 wk after AST; isolates from 101 episodes genotyped 5 (5%) clinical CDI isolates highly related to strains from 3 CD carriers: Asymptomatic carriers (from LTCFs or inpatients), particularly those with skin and/or environmental shedding, may contribute to CD transmission in hospitals 1 Donskey CJ. IDWeek 2014 abs. 529 2 Galdys A. IDWeek 2014 abs. 1646 2 of 2 Data from poster Hospital-acquired (during 12-wk period after AST) Probable transmission: pts with highly related isolates + simultaneous occupancy of the same inpatient ward; possible transmission: highly related isolates + simultaneous occupancy of hospital but not same inpatient ward

3. Impact of individual-level and ward-level antibiotic exposure on patient risk of Clostridium difficile infection (CDI) Single-centre cohort study (Canada): N=34,298 unique pts >18 yr (median age: 68.4 yr), without previous CDI diagnosis, hospitalised in acute care ward (16 wards) in period 01/06/2010-31/03/2012 (428,588 patient-days) 45.5% of hospitalisations received antibiotics (AB) Unadjusted patient-level risk factors for CDI (Poisson regression analysis) Unadjusted ward-level risk factors for CDI (weighted linear regression): AB use: stronger risk factor than hand hygiene, antacid or feeding tube use CDI risk ↑ with ward AB use, both in pts with and without direct AB exposure Brown K. IDWeek 2014 abs. 1795 1 of 2 Data from oral presentation

4. Impact of individual-level and ward-level antibiotic exposure on patient risk of Clostridium difficile infection (CDI) Multi-level model (Poisson regression with random intercepts for ward) Ward-level antibiotic exposure seems to be one of the strongest risk factors for CDI Brown K. IDWeek 2014 abs. 1795 2 of 2 Data from oral presentation