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Nosocomial infection

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A nosocomial infection is an infectionthat is caused by staying in a hospital. An infection is considered nosocomial if it occurs 48 hours or more after a hospital admission. The word comes from the Greekword nosokomeion meaning hospital (nosos = disease, komeo = to take care of ). A related term is iatrogenicdisease. The most common nosocomial infections are of the urinary tract, and the second most common are pneumonias.

In the United States, it has been estimated that as many as one hospital patient in ten acquires a nosocomial infection, or 2 million patients a year. Estimates of the annual cost range from $4.5 billion to $11 billion and up. Nosocomial infections contributed to 88,000 deaths in the U.S. in 1995. One third of nosocomial infections are considered preventable.

Nosocomial infections are even more alarming in the 21st century as antibiotic resistancespreads. Reasons why nosocomial infections are so common include:

  • Hospitals house large numbers of people who are sick and whose immune systemsare often in a weakened state.
  • increased use of outpatient treatment means that people who are in the hospital are sicker on average.
  • medical staff move from patient to patient, providing a way for pathogens to spread.
  • many medical procedures bypass the body's natural protective barriers.
  • routine use of anti-microbial agents in hospitals creates selection pressurefor the emergence of resistant strains.

Thorough hand washingby all medical personnel before each patient contact is one of the most effective ways to combat nosocomial infections. More careful use of anti-microbialagents, such as antibiotics, is also considered vital.


  • 1 Rationale For Isolation Precautions In Hospitals
  • 2 Source
  • 3 Host
  • 4 Pathogens
    • 4.1 Bacteria
    • 4.2 Viruses
    • 4.3 Parasites and Fungi
  • 5 Transmission
  • 6 Predisposition to infection
  • 7 Isolation
    • 7.1 Handwashing and Gloving
    • 7.2 Patient Placement
    • 7.3 Transport of Infected Patients
    • 7.4 Masks, Respiratory Protection, Eye Protection, Face Shields
    • 7.5 Gowns and Protective Apparel
    • 7.6 Patient-Care Equipment and Articles
    • 7.7 Linen and Laundry
    • 7.8 Routine and Terminal Cleaning

Rationale For Isolation Precautions In Hospitals

Transmission of infection within a hospital requires three elements: a source of infecting microorganisms, a susceptible host, and a means of transmission for the microorganism.


Human sources of the infecting microorganisms in hospitals may be patients, personnel, or, on occasion, visitors, and may include persons with acute disease, persons in the incubation period of a disease, persons who are colonized by an infectious agent but have no apparent disease, or persons who are chroniccarriers of an infectious agent. Other sources of infecting microorganisms can be the patient's own endogenous flora, which may be difficult to control, and inanimate environmental objects that have become contaminated, including equipment and medications.


People are at the centre of hospital acquired infection: as a reservoir or source of microorganisms, as the transmitter of microorganisms and as a receptor for microorganisms ? thus becoming a reservoir themselves and beginning the cycle anew. Infections tend to be endemicas opposed to epidemic, either coming from another person in the hospital (cross-infection), from an inanimate object recently contaminated by a human source (environmental infection) or may be caused by a patient?s own flora (endogenous infection). The majority of infections are caused by organisms common in the general population, in whom they are generally subclinical.

Gram-positiveinfectionsare becoming increasingly common ? their hallmark being ever higher resistance to antimicrobialagents. There have also been relative increases in small (but important) groups of pathogensthat were previously uninvolved ? coagulasenegative cocciand coryneforms(flora from the skin of medical professionals). Staph. aureushas become more significant, especially given rises in resistance against methicillinand some aminoglycosides? methicillin resistance is now at about 55%. This can be blamed on using broad-spectrum antibiotic treatment as a reflex action, as opposed to narrow-spectrum treatment only once a definite infectious process has been identified.



These are the most common nosocomial pathogens and can be divided into:

  • Commensalbacteriafound in normal floraof healthy humans. These have a significant protective role by preventing colonizationby pathogenicmicroorganisms. Some commensal bacteria may cause infection if the natural host is compromised. For example, cutaneouscoagulasenegative staphylococci cause intravascularline infection and intestinal Escherichia coli are the most common cause of urinary infection.
  • Pathogenicbacteriahave greater virulence, and cause infections (sporadicor epidemic) regardless of host status. For example:
    • AnaerobicGram-positiverods (e.g. Clostridium) cause gangrene.
    • Gram-positivebacteria: Staphylococcus aureus (cutaneousbacteria that colonize the skin and nose of both hospital staff and patients) cause a wide variety of lung, bone, heart and bloodstream infections and are frequently resistant to antibiotics; beta-haemolyticstreptococci are also important.
    • Gram-negativebacteria: Enterobacteriacae (e.g. Escherichia coli, Proteus, Klebsiella, Enterobacter, Serratia marcescens), may colonizesites when the host defences are compromised. They may also be highly resistant.
    • Gram-negativeorganisms such as Pseudomonas spp. are often isolated in water and damp areas. They may colonize the digestive tract of hospitalized patients.
    • Selected other bacteria are a unique risk in hospitals. For instance, Legionella species may cause pneumonia(sporadic or endemic) through inhalation of aerosolscontaining contaminated water (air conditioning, showers, therapeutic aerosols).


There is the possibility of nosocomial transmission of many viruses, including the hepatitisB and C viruses (transfusions, dialysis, injections, endoscopy), respiratory syncytial virus (RSV), rotavirus, and enteroviruses (transmitted by hand-to-mouth contact and via the faecal-oral route). Other viruses such as cytomegalovirus, HIV, Ebola, influenzaviruses, herpes simplex virus, and varicella-zoster virus, may also be transmitted.

Parasites and Fungi

Some parasites(e.g. Giardia lamblia) are transmitted easily among adults or children. Many fungiand other parasitesare opportunisticorganisms and cause infections during extended antibiotictreatment and severe immunosuppression(Candida albicans, Aspergillusspp., Cryptococcus neoformans, Cryptosporidium). These are a major cause of systemic infections among immunocompromisedpatients. Environmental contamination by airborne organisms such as Aspergillusspp. which originate in dust and soil is also a concern, especially during hospital construction. Sarcoptesscabies (scabies) is an ectoparasite which has repeatedly caused outbreaks in health care facilities.


Microorganisms are transmitted in hospitals by several routes, and the same microorganism may be transmitted by more than one route. There are five main routes of transmission -- contact, droplet, airborne, common vehicle, and vectorborne.

  • Contact transmission, the most important and frequent mode of transmission of nosocomial infections, is divided into two subgroups: direct-contact transmission and indirect-contact transmission.
    • Direct-contact transmission involves a direct body surface-to-body surface contact and physical transfer of microorganisms between a susceptible host and an infected or colonized person, such as occurs when a person turns a patient, gives a patient a bath, or performs other patient-careactivities that require direct personal contact. Direct-contact transmission also can occur between two patients, with one serving as the source of the infectious microorganisms and the other as a susceptible host.
    • Indirect-contact transmission involves contact of a susceptible host with a contaminated intermediate object, usually inanimate, such as contaminated instruments, needles, or dressings, or contaminated hands that are not washed and gloves that are not changed between patients.
  • Droplet transmission, theoretically, is a form of contact transmission. However, the mechanism of transfer of the pathogen to the host is quite distinct from either direct- or indirect-contact transmission. Therefore, droplet transmission can be considered a separate route of transmission. Droplets are generated from the source person primarily during coughing, sneezing, and talking, and during the performance of certain procedures such as suctioningand bronchoscopy. Transmission occurs when droplets containing microorganisms generated from the infected person are propelled a short distance through the air and deposited on the host's conjunctivae, nasal mucosa, or mouth. Because droplets do not remain suspended in the air, special air handling and ventilation are not required to prevent droplet transmission; that is, droplet transmission must not be confused with airborne transmission.
  • Airborne Transmission occurs by dissemination of either airborne droplet nuclei (small-particle residue {5 μmor smaller in size} of evaporated droplets containing microorganisms that remain suspended in the air for long periods of time) or dust particles containing the infectious agent. Microorganisms carried in this manner can be dispersed widely by air currents and may become inhaled by a susceptible host within the same room or over a longer distance from the source patient, depending on environmental factors; therefore, special air handling and ventilation are required to prevent airborne transmission. Microorganisms transmitted by airborne transmission include Mycobacterium tuberculosis and the rubeola and varicella viruses.
  • Common Vehicle Transmission applies to microorganisms transmitted by contaminated items such as food, water, medications, devices, and equipment.
  • Vectorborne Transmission occurs when vectorssuch as mosquitoes, flies, rats, and other vermintransmit microorganisms.

Predisposition to infection

Factors predisposing a patient to infection can broadly be divided into four areas:

  • People in hospitals are usually already in a poor state of health, impairing their defence against bacteria ? advanced age or premature birthalong with immunocompromisation(due to drugs, illness or irradiation) present a general risk, while other diseases can present specific risks - for instance chronic lung diseasecan increase chances of respiratory tract infection.
  • Acute disease can greatly increase the risk of infection ? burnsand traumacause the loss of skin, an important barrier against infection.
  • Invasive devices, for instance intubationtubes, catheters, surgical drains and tracheostomytubes all bypass the body?s natural lines of defence against pathogensand prevent an easy route for infection. Patients already colonised on admission are instantly put at greater risk when they undergo an invasive procedure.
  • A patient?s treatment itself can leave them vulnerable to infection ? immunosuppressionand antacidtreatment undermine the body?s defences, while antimicrobialtherapy (removing competitive floraand only leaving resistant organisms), recurrent bloodtransfusions, parenteral nutritionand remaining in a recumbent position have all been identified as risk factors.


Isolation precautions are designed to prevent transmission of microorganisms by these routes in hospitals. Because agent and host factors are more difficult to control, interruption of transfer of microorganisms is directed primarily at transmission.

Placing a patient on isolation precautions, however, often presents certain disadvantages to the hospital, patients, personnel, and visitors. Isolation precautions may require specialized equipment and environmental modifications that add to the cost of hospitalization. Isolation precautions may make frequent visits by nurses, physicians, and other personnel inconvenient, and they may make it more difficult for personnel to give the prompt and frequent care that sometimes is required. The use of a multi-patient room for one patient uses valuable space that otherwise might accommodate several patients. Moreover, forced solitude deprives the patient of normal social relationships and may be psychologically harmful, especially to children. These disadvantages, however, must be weighed against the hospital's mission to prevent the spread of serious and epidemiologically important microorganisms in the hospital.

A variety of infection control measures are used for decreasing the risk of transmission of microorganisms in hospitals. These measures make up the fundamentals of isolation precautions.

Handwashing and Gloving

Handwashing frequently is called the single most important measure to reduce the risks of transmitting microorganisms from one person to another or from one site to another on the same patient.

Washing hands as promptly and thoroughly as possible between patient contacts and after contact with blood, body fluids, secretions, excretions, and equipment or articles contaminated by them is an important component of infection control and isolation precautions. In addition to handwashing, gloves play an important role in reducing the risks of transmission of microorganisms.

Glovesare worn for three important reasons in hospitals. First, gloves are worn to provide a protective barrier and to prevent gross contamination of the hands when touching blood, body fluids, secretions, excretions, mucous membranes, and nonintact skin; the wearing of gloves in specified circumstances to reduce the risk of exposures to bloodborne pathogensis mandated by the OSHA Bloodborne Pathogens final rule. Second, gloves are worn to reduce the likelihood that microorganisms present on the hands of personnel will be transmitted to patients during invasive or other patient-care procedures that involve touching a patient's mucous membranes and nonintact skin. Third, gloves are worn to reduce the likelihood that hands of personnel contaminated with microorganisms from a patient or a fomite can transmit these microorganisms to another patient. In this situation, gloves must be changed between patient contacts and hands should be washed after gloves are removed.

Wearing gloves does not replace the need for handwashing, because gloves may have small, apparent defects or may be torn during use, and hands can become contaminated during removal of gloves. Failure to change gloves between patient contacts is an infection control hazard.

Patient Placement

Appropriate patient placement is a significant component of isolation precautions. A private room is important to prevent direct- or indirect-contact transmission when the source patient has poor hygienichabits, contaminates the environment, or cannot be expected to assist in maintaining infection control precautions to limit transmission of microorganisms (ie, infants, children, and patients with altered mental status). When possible, a patient with highly transmissible or epidemiologicallyimportant microorganisms is placed in a private room with handwashing and toilet facilities, to reduce opportunities for transmission of microorganisms.

When a private room is not available, an infected patient is placed with an appropriate roommate. Patients infected by the same microorganism usually can share a room, provided they are not infected with other potentially transmissible microorganisms and the likelihood of reinfection with the same organism is minimal. Such sharing of rooms, also referred to as cohorting patients, is useful especially during outbreaks or when there is a shortage of private rooms. When a private room is not available and cohorting is not achievable or recommended, it is very important to consider the epidemiology and mode of transmission of the infecting pathogen and the patient population being served in determining patient placement. Under these circumstances, consultation with infection control professionals is advised before patient placement. Moreover, when an infected patient shares a room with a noninfected patient, it also is important that patients, personnel, and visitors take precautions to prevent the spread of infection and that roommates are selected carefully.

A private room with appropriate air handling and ventilation is particularly important for reducing the risk of transmission of microorganisms from a source patient to susceptible patients and other persons in hospitals when the microorganism is spread by airborne transmission. Some hospitals use an isolation room with an anteroom as an extra measure of precaution to prevent airborne transmission.

Transport of Infected Patients

Limiting the movement and transport of patients infected with virulent or epidemiologically important microorganisms and ensuring that such patients leave their rooms only for essential purposes reduces opportunities for transmission of microorganisms in hospitals. When patient transport is necessary, it is important that (1) appropriate barriers (eg, masks, impervious dressings) are worn or used by the patient to reduce the opportunity for transmission of pertinent microorganisms to other patients, personnel, and visitors and to reduce contamination of the environment; (2) personnel in the area to which the patient is to be taken are notified of the impending arrival of the patient and of the precautions to be used to reduce the risk of transmission of infectious microorganisms; and, (3) patients are informed of ways by which they can assist in preventing the transmission of their infectious microorganisms to others.

Masks, Respiratory Protection, Eye Protection, Face Shields

Various types of masks, goggles, and face shields are worn alone or in combination to provide barrier protection. A mask that covers both the nose and the mouth, and goggles or a face shield are worn by hospital personnel during procedures and patient care activities that are likely to generate splashes or sprays of blood, body fluids, secretions, or excretions to provide protection of the mucous membranes of the eyes, nose, and mouth from contact transmission of pathogens. The wearing of masks, eye protection, and face shields in specified circumstances to reduce the risk of exposures to bloodborne pathogens is mandated by the OSHA bloodborne pathogens final rule. A surgical mask generally is worn by hospital personnel to provide protection against spread of infectious large-particle droplets that are transmitted by close contact and generally travel only short distances (up to 3 ft) from infected patients who are coughing or sneezing. An area of major concern and controversy over the last several years has been the role and selection of respiratory protection equipment and the implications of a respiratory protection program for prevention of transmission of tuberculosisin hospitals. Traditionally, although the efficacy was not proven, a surgical mask was worn for isolation precautions in hospitals when patients were known or suspected to be infected with pathogens spread by the airborne route of transmission. In 1990, however, the CDC tuberculosis guidelines stated that surgical masks may not be effective in preventing the inhalation of droplet nuclei and recommended the use of disposable particulate respirators, despite the fact that the efficacy of particulate respiratorsin protecting persons from the inhalation of M tuberculosis had not been demonstrated.

Gowns and Protective Apparel

Various types of gowns and protective apparel are worn to provide barrier protection and to reduce opportunities for transmission of microorganisms in hospitals. Gowns are worn to prevent contamination of clothing and to protect the skin of personnel from blood and body fluid exposures. Gowns especially treated to make them impermeable to liquids, leg coverings, boots, or shoe covers provide greater protection to the skin when splashes or large quantities of infective material are present or anticipated. The wearing of gowns and protective apparel under specified circumstances to reduce the risk of exposures to bloodborne pathogens is mandated by the OSHA Bloodborne Pathogens final rule.

Gowns also are worn by personnel during the care of patients infected with epidemiologically important microorganisms to reduce the opportunity for transmission of pathogens from patients or items in their environment to other patients or environments; when gowns are worn for this purpose, they are removed before leaving the patient's environment, and hands are washed. Adequate data regarding the efficacy of gowns for this purpose, however, is not available.

Patient-Care Equipment and Articles

Many factors determine whether special handling and disposal of used patient-care equipment and articles are prudent or required, including the likelihood of contamination with infective material; the ability to cut, stick, or otherwise cause injury (needles, scalpels, and other sharp instruments); the severity of the associated disease; and the environmental stability of the pathogens involved. Some used articles are enclosed in containers or bags to prevent inadvertent exposures to patients, personnel, and visitors and to prevent contamination of the environment. Used sharps are placed in puncture-resistant containers; other articles are placed in a bag. One bag is adequate if the bag is sturdy and the article can be placed in the bag without contaminating the outside of the bag; otherwise, two bags are used.

Contaminated, reusable critical medical devices or patient-care equipment (ie, equipment that enters normally sterile tissue or through which blood flows) or semicritical medical devices or patient-care equipment (ie, equipment that touches mucous membranes) are sterilized or disinfected (reprocessed) after use to reduce the risk of transmission of microorganisms to other patients; the type of reprocessing is determined by the article and its intended use, the manufacturer's recommendations, hospital policy, and any applicable guidelines and regulations.

Noncritical equipment (ie, equipment that touches intact skin) contaminated with blood, body fluids, secretions, or excretions is cleaned and disinfected after use, according to hospital policy. Contaminated disposable (single-use) patient-care equipment is handled and transported in a manner that reduces the risk of transmission of microorganisms and decreases environmental contamination in the hospital; the equipment is disposed of according to hospital policy and applicable regulations.

Linen and Laundry

Although soiled linen may be contaminated with pathogenic microorganisms, the risk of disease transmission is negligible if it is handled, transported, and laundered in a manner that avoids transfer of microorganisms to patients, personnel, and environments. Rather than rigid rules and regulations, hygienic and common sense storage and processing of clean and soiled linen are recommended. The methods for handling, transporting, and laundering of soiled linen are determined by hospital policy and any applicable regulations.

Routine and Terminal Cleaning

The room, or cubicle, and bedside equipment of patients on Transmission-Based Precautions are cleaned using the same procedures used for patients on Standard Precautions, unless the infecting microorganism(s) and the amount of environmental contamination indicate special cleaning. In addition to thorough cleaning, adequate disinfection of bedside equipment and environmental surfaces (eg, bed rails, bedside tables, carts, commodes, doorknobs, faucet handles) is indicated for certain pathogens, especially enterococci, which can survive in the inanimate environment for prolonged periods of time. Patients admitted to hospital rooms that previously were occupied by patients infected or colonized with such pathogens are at increased risk of infection from contaminated environmental surfaces and bedside equipment if they have not been cleaned and disinfected adequately. The methods, thoroughness, and frequency of cleaning and the products used are determined by hospital policy.

This article contains text from the public domain resource by the Centers for Disease Control and Prevention, found hereand the World Health Organisation, found here.de:Nosokomiale Infektion fr:Infection nosocomiale sk:Nemocni?ná nákaza fi:Sairaalabakteeri

Retrieved from "http://en.wikipedia.org/Nosocomial_infection"

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It uses material from the http://en.wikipedia.org/wiki/Nosocomial+infection Wikipedia article Nosocomial infection.

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