Table 1.

Summary of Best Quality Evidence by transmission Pathway

First Author, Year	Title	Study Design	Population	Relevant Objective	Related Molecular Analysis	Related Finding
1. Transmission from patient to HCW
Morgan DJ et al 20128	Transfer of multidrug-resistant bacteria to HCW gloves and gowns after patient contact increases with environmental contamination.	Prospective cohort study	27 HCW–patient interactions: 256 patient samples, 1,572 environmental sites, 131 pairs of HCW hands from the MICU of Rush University Medical Center	To estimate the level of hand or glove contamination with VRE among HCWs when interacting with the patient or environment	PFGE	Of 103 HCWs whose hand samples were negative for VRE when they entered the room, 70% contaminated their hands/gloves after interacting with the patient and the environment.
Morgan DJ et al 20109	Frequent MDR A. baumannii contamination of gloves, gowns, and hands of HCWs	Prospective cohort study	199 patient–HCW interactions in 48 ICUs at University of Maryland Medical Center	To determine the incidence of transmission of MDR A. baumannii and P. aeruginosa from patients to HCWs during routine care	PFGE	39% of patient–HCW interactions resulted in HCW G&G contamination with A. baumannii. 9 (5%) episodes resulted in hand contamination after G&G removal; isolates were identical to the G&G strain. 8% of patient–HCW interactions resulted in HCW G&G contamination with MDR P. aeuroginosa (imipenem resistant).
Hayden, M.K. et al 200816	Risk of hand or glove contamination after contact with patients colonized with VRE or the colonized patients’ environment	Prospective cohort study	603 patient–HCW interactions in 6 different ICUs at University of Maryland Medical Center	To assess the role of environmental contamination in the transmission of MDROs to HCW clothing	PFGE	33% of P-HCW interactions led to transmission of MDR A. baumannii to HCW G&G. Carbapenem-resistant P. aeruginosa was transmitted 17% of the time. MRSA and VRE were transmitted 14% of time. Of 22 cases (selected for PFGE), 82% of HCW had a strain related to the patient.
Schweizer M et al 201217	The epidemiology of MRSA on a burn trauma unit	Prospective cohort study	144 patients, 67 HCWs and 50 environmental samples from the burn trauma unit at a midwestern academic medical center	To determine whether HCW, environment, or admitted patients could be reservoirs for MRSA	PFGE	The USA100 subtype was shared by 3 patients and 1 HCW. In these cases, at least 1 patient was positive before the HCW was.
2. Transmission from patient to environment
Munoz-Price LS et al 201311	A. baumannii: association between environmental contamination of patient rooms and occupant status	Prospective cohort study	186 air samples and 82 clinical specimens from Turgut Ozal Medical Center	To understand the dynamics of Acinetobacter spread in air	PCR-typing (DiversLab) PFGE	The Acinetobacter concentration was the highest in bedside sampling areas of infected patients. Air isolates were clonally related to clinical strains.
Thom KA et al 201112	Environmental contamination because of multidrug-resistant A. baumannii surrounding colonized or infected patients.	Randomized sequential sampling of bed areas	2,436 environmental samples around 114 patients; 349 samples from HCWs hands and phones from ICUs from 2 London teaching hospitals	To assess the degree of environmental contamination with MRSA in critical care and the likelihood of subsequent new patient acquisition	Phage typing	Of 52 patients colonized with MRSA, 34 (65%) had similar strains found consequently in their environment.
Yakupogullari Y et al 200618	Is airborne transmission of A. baumannii possible? A prospective molecular epidemiologic study in a tertiary-care hospital	Prospective cohort study	479 environmental samples from 50 unique patient rooms in 4 ICUs at University of Maryland Medical Center	To determine how frequently the environment surrounding the patient becomes contaminated	PGFE	48% (24/50) of the rooms were positive for MDR A. baumannii. In 17 of 20 instances (85%) (among patients with MDR A. baumannii history), environmental isolates were genetically similar to the patient isolate.
Wilson AP et al 200719	Importance of the environment for patient acquisition of MRSA in the ICU: a baseline study	Prospective cohort study	628 ICU rooms at a county teaching hospital	To determine the association between room contamination and the status of the occupants	PFGE	39% of rooms with A. baumannii positive patients were contaminated. 10% of rooms with A. baumannii–negative patients were contaminated as well. 6 of 7 instances (86%), environmental isolates were genetically similar to the patient isolate.
3. Transmission from HCW to patient
Wilson AP et al 200719	Importance of the environment for patient acquisition of MRSA in the ICU: a baseline study	Randomized sequential sampling of bed areas	2,436 environmental samples around 114 patients, 349 samples from HCWs hands and phones from ICUs from 2 London teaching hospitals	To assess the degree of environmental contamination with MRSA in critical care and the likelihood of subsequent new patient acquisition	Phage typing	5 (45%) patients became colonized but with different MRSA strains than the ones in their environment. 25 out 31 (81%) HCW hands were positive for MRSA; however, in no instances were these strains subsequently acquired by patients.
Ben-David D et al 200820	MRSA transmission: the possible importance of unrecognized HCW carriage	Prospective cohort study	19 burn patients, 133 HCWs from the TICU in Rhode Island Hospital	To detect MRSA acquisition and its source	PFGE	7 patients and 4 HCWs harbored the same clone A. 2 patients and 1 HCW harbored clone B. Once the HCWs were successfully decolonized, a sustained reduction in MRSA infections occurred.
Loftus RW et al 201521	The epidemiology of S. aureus transmission in the anesthesia work area	Prospective cohort study	2,170 environmental sites, 2,640 HCW hand cultures, 1,087 patient skin samples from 274 case pairs across 3 major US academic medical centers.	To characterize the epidemiology of bacterial transmission events in the anesthesia work area	PFGE	2 main phenotypes were identified (P and H). Strong evidence that patient-derived strains were transmitted to subsequent patients who had procedures on the same day. Their primary routes were the environment (66%) and HCW hands (80%).
4. Transmission from environment to patient
Yakupogullari Y et al 200618	Is airborne transmission of A. baumannii possible? A prospective molecular epidemiologic study in a tertiary-care hospital	Prospective cohort study	186 air samples and 82 clinical specimens from Turgut Ozal Medical Center	To understand the dynamics of Acinetobacter spread in air	PCR-typing (DiversLab) PFGE	Epidemiological links were found between strains isolated in the air and strains isolated from clinical samples taken from patients discharged weeks earlier and patients who were hospitalized >3 mo later.
Wilson AP et al 200719	Importance of the environment for patient acquisition of MRSA in the ICU: a baseline study	Randomized sequential sampling of bed areas	2,436 environmental samples around 114 patients, 349 samples from HCWs hands and phones from ICUs from 2 London teaching hospitals	To assess the degree of environmental contamination with MRSA in critical care and the likelihood of subsequent new patient acquisition	Phage typing	1 patient (2%) subsequently acquired the MRSA in the environment. 5 other patients (11%) became colonized but with different MRSA strains than those in their environment.
Loftus RW et al 201521	The epidemiology of S. aureus transmission in the anesthesia work area	Prospective cohort study	939 screened patients and 1252 environmental samples in a tertiary acute-care hospital	To investigate the possible routes of transmission of MRSA between MRSA positive patients	spa dru PFGE	Based on epidemiological investigation, 44 cross-transmission cases were identified. Cross-transmission was confirmed molecularly 25% of the time (11/44). In the 11 confirmed cases, patients were the source in 6 instances (55%), patient and the environment in three cases (27%), and only the environment on two instances (18%).
Creamer E et al 201222	Transmission of endemic ST22MRSA-IV on four acute hospital wards investigated using a combination of spa, dru and PFGE typing	Prospective cohort study	2,170 environmental sites, 2,640 HCW hand cultures, 1,087 patient skin samples from 274 case-pairs across 3 major US academic medical centers	To characterize the epidemiology of bacterial transmission events in the anesthesia work area	PFGE	2 main phenotypes were identified (P and H). Strong evidence that patient-derived strains were transmitted to subsequent patients who had procedures on the same day. Their primary routes were the environment (66%) and HCW hands (80%).
5. Transmission from environment to HCW
Morgan D et al 20128	Transfer of multidrug-resistant bacteria to HCWs’ gloves and gowns after patient contact increases with environmental contamination	Prospective cohort study	603 P-HCW interactions in 6 different ICUs at the University of Maryland Medical Center	To assess the role of environmental contamination in the transmission of MDROs to HCW clothing	PFGE	33% of P-HCW interactions led to transmission of MDR A. baumannii to HCW G&G. Carbapenem-resistant P. aeruginosa was transmitted 17% of the time. MRSA and VRE were transmitted 14% of time. Of 22 cases, 91% had a strain related to the environment.
Hayden MK et al 200816	Risk of hand or glove contamination after contact with patients colonized with VRE or the colonized patients’ environment	Structured observational study	27 HCW–patient interactions: 256 patient samples, 1,572 environmental sites, 131 pairs of HCW hands from the MICU of Rush University Medical Center	To estimate the level of hand or glove contamination with VRE among HCW when interacting with the patient or environment	PFGE	From 103 HCWs whose hand samples were negative for VRE when they entered the room, 52% contaminated their hands/gloves after touching the environment, and 70% contaminated their hands/gloves after interacting with the patient and the environment.
Barbolla RE et al 200823	Molecular epidemiology of A. baumannii spread in an adult ICU under an endemic setting	Prospective cohort study	65 newly admitted patients, 378 environmental samples and 93 HCW hands from the adult ICU at the Sanatorio de la Trinidad-Mitre	To assess the prevalence of carbapenem-resistant clones and their way of spread	PFGE	Frequently touched surfaces close to contaminated patients seemed to play a role in transmissibility perhaps through enhancing staff hand carriage. The decrease of clone if hand carriage correlated with discharge of the last patient with this clone but also its decrease in the environment. The role of personnel hand carriage in environmental contamination was also evident.

Note. G&G, gowns and gloves; HCW, healthcare worker; ICU, intensive care unit; MDR, multidrug resistant; MDRO, multidrug-resistant organisms; MICU, medical intensive care unit; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus; PFGE, Pulse-field gel electrophoresis; P-HCW, patient to HCW; spa, Staphylococcus protein A; TICU, trauma intensive care unit; VRE, vancomycin-resistant Enterococcus.