A set of training materials for professionals working in intervention epidemiology, public health microbiology and infection control and hospital hygiene.
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1. Environment and Risk of Infection.
Many scientific evidences support the role of the inanimate environment as a source of Healthcare-Associated Infections (HAIs). Transmission can happen through air or through contact.
1.1 Air transmission.
Potential reservoirs of infections conveyed through air are the following:
building materials, during maintenance and/or renovation works: in this case Aspergillus and other filamentous fungi are most likely to be involved as infectious agents. Subjects with low immune defenses are at highest risk;
water reservoirs, such as humidifiers, nebulizers and sinks can be the source for Acinetobacter spp, Pseudomonas aeruginosa, Aspergillus, and Legionella pneumophila. Legionella can also be spread by the hot water network and the heating, ventilation and air conditioning system.
1.2 Contact transmission.
The transmission can occur through direct or indirect contact. The potential sources of infection are:
These microorganisms can spread through the colonized or infected patient (who is also sometimes carrier of invasive devices such as tracheal or tracheostomy tubes, central venous catheters - CVC, urinary catheters), can survive on surfaces for a long time and are difficult to eradicate by cleaning and disinfection [1,2].
Environmental contamination can occur directly, through shared use of contaminated medical devices, and, most frequently, indirectly, usually through the hands of healthcare workers (HCW).
Alternative healthcare settings (outpatient treatment services, homecare, rehabilitation and long-term care facilities), which may not warrant the standards required to acute care hospitals in terms of HCWs numbers and competence and environmental cleanliness and maintenance, and the emergence and spread of antibiotic multidrug or pan-resistant organisms, especially of gram-negative bacteria, may be also at risk.
2. Environmental localization and survival of microorganisms
In 2003 the CDC pointed out the need to ensure proper environmental hygiene standards, especially for high touch surfaces .
The environmental surfaces most commonly involved as a source of contamination / transmission are:
surfaces in the immediate surrounding patient's area (e.g. bed rails, bedside table, bed table, call buttons );
surfaces commonly touched by patients and healthcare workers (e.g. toilet door handles, toilets);
shared use devices (e.g. stethoscopes, glucometers);
surfaces regularly touched by healthcare workers (e.g. mobile and office phones, tablets, keyboards and mouses, touch screen monitors).
Gram-positive (such as MRSA and VRE, even in dry conditions) and Gram-negative MDR organisms have been documented to survive on environmental surfaces, especially on those closest to the patient. According to many authors, the most common way of transmission is due to gloves contaminated while delivering care to the patient.
Distribution of microorganisms on environmental surfaces depends on the prevalence of contaminants in the treated population and on their ability to survive in the environment in different conditions (e.g. dryness or wetness).
There are some microbiological factors that may facilitate transmission of pathogens from environmental surfaces, particularly:
survival for long periods on surfaces;
persistent virulence after environmental exposure;
ability to transiently colonize HCWs hands, which become carriers of transmission ;
ability to colonize the patients. This is particularly important for Acinetobacter, Clostridium difficile, VRE, MRSA, CPE;
very low infectious dose. Typical examples are Clostridium difficile, which needs only 7 spores to be infective, and norovirus, whose transmissibility is determined by 10-100 virions;
ability of attaching to surfaces, that may lead to biofilm formation.
Biofilm is an assemblage of surface-structured communities of one or more species in which microorganisms are wrapped and protected by esopolymeric substances (EPS). It protects microorganisms from drying, helps their attachment to surfaces, and reduces the effectiveness of both chemical (disinfectants) or physical (e.g. UV rays) biocides and antibiotics.
Microorganisms adhering to the surfaces represent an intermediate step and have a lower susceptibility to biocides than planktonic cells; susceptibility becomes much lower when biofilm is structured. Occasionally, biofilm releases free microorganisms and, although they regain their original sensivity to biocides, they are still potential agents of infection.
Biofilm can affect healthcare wet surfaces, such as medical devices ( including endoscope channels and prosthetic devices), as well as dry surfaces, including environmental ones.
Moreover, adhesion to surfaces increases the resistance to physical removal, made through cleaning (resilience), mostly due to the esopolymeric matrix. [4,5].
Many evidences show that an environment previously occupied by a patient colonized or infected with a pathogen, and not properly treated, constitutes an important risk factor for colonization or infection with the same pathogen for the next patient [6-9].
Consequently, all healthcare workers need to be educated about the importance of maintaining a clean and safe care environment for patients. Every healthcare worker needs to know their specific responsibilities for cleaning and decontaminating the clinical environment and the equipment used in patient care.
Otter JA, Yezli S, Salkeld JA, French GL. Evidence that contaminated surfaces contribute to the transmission of hospital pathogens and an overview of strategies to address contaminated surfaces in hospital settings. Am J Infect Control. 2013 May;41 (5 Suppl): S6-11.
Moore G, Muzslay M, Wilson AP. The type, level, and distribution of microorganisms within the ward environment: a zonal analysis of an intensive care unit and a gastrointestinal surgical ward. Infect Control Hosp Epidemiol. 2013May; 34 (5): 500-6.
Guidelines for environmental infection control in health-care facilities. Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). Atlanta: U.S. Department of Health and Human Services; 2003.
Otter JA, Vickery K, Walker JT, de Lancey Pulcini E, Stoodley P, Goldenberg SD, et al. Surface-attached cells, biofilms and biocide susceptibility: implications for hospital cleaning and disinfection. J Hosp Infect. 2015 Jan;89 (1): 16-27.
Vickery K, Deva A, Jacombs A, Allan J, Valente P, Gosbell IB. Presence of biofilm containing viable multiresistant organisms despite terminal cleaning on clinical surfaces in an intensive care unit. J Hosp Infect. 2012 Jan;80 (1): 52-5.
Huang SS, Datta R, Platt R. Risk of acquiring antibiotic-resistant bacteria from prior room occupants. Arch Intern Med. 2006 Oct 9;166 (18):1945-51.
Drees M, Snydman DR, Schmid CH, Barefoot L, Hansjosten K, Vue PM, et al. Prior environmental contamination increases the risk of acquisition of vancomycin-resistant enterococci. Clin Infect Dis. 2008 Mar1;46 (5): 678-85.
Nseir S, Blazejewski C, Lubret R, Wallet F, Courcol R, Durocher A. Risk of acquiring multidrug-resistant Gram-negative bacilli from prior room occupants in the intensive care unit. Clin Microbiol Infect. 2011 Aug;17 (8): 1201-8.
Shaughnessy MK, Micielli RL, De Pestel DD, Arndt J, Strachan CL, Welch KB, et al. Evaluation of hospital room assignment and acquisition of Clostridium difficile infection. Infect Control Hosp Epidemiol. 2011 Mar;32 (3): 201-6.
Original contribution from:
Gaetano Privitera, Dept of Translational Medicine, University of Pisa, Italy.
Cesarina Curti, Scientific Committee, SIMPIOS, Società Italiana per la Prevenzione delle Infezioni nelle Organizzazioni Sanitarie, Italy.
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