What are hospital or nosocomial infections?

The Nosocomial infections (from the Latin nosocomīum, “hospital”), also known as hospital infections or hospital-acquired infections, are infections acquired in a hospital, although currently nosocomial infections are usually understood as all healthcare-associated infectionsincluding care outside and within health centers, for example in home care.

However, specifically hospital-acquired nosocomial infections tend to have the greatest impact, with millions of people affected and thousands of deaths annually worldwidealthough international comparisons are very difficult to carry out due to the different definitions, types of nosocomial infections covered, health units from which the data come, and many other variables.


Nosocomial infections are defined, according to the World Health Organization, as infectious diseases spread unintentionally during health care, or acquired during a stay in a hospital or health center.

To be considered a nosocomial infection, the infection must not have manifested or been in the incubation period before admission to the hospital or receiving health care, nor should it be the cause of the admission or care.

infections acquired in Intensive Care Units They are one of the best studied types of nosocomial infections, since they are also one of the most common, since they are serious patients who usually have a diminished immune system.

There is no clear limit of when an infection that occurs in the hospital setting is no longer considered a community infection and begins to be considered a nosocomial infection. Various studies set highly variable limits, from 2 to 5 days (48-120 hours).

Types, causes and routes of transmission

There are many types of nosocomial infections, but four are the most common:

  • hospital pneumoniaespecially that associated with ventilation systems.
  • urinary tract infections
  • Stomach flu
  • Fever or puerperal infection (during the delivery)

Infections can be spread to susceptible patients by direct contact between people, through utensils and machinery or through air, and may have its origin outside the center, in another patient, in the health personnel, the patient's own flora or reservoirs in the utensils, machinery and health facilities. For example, ventilation ducts They are frequent reservoirs of certain bacteria and fungi.

The most important and frequent route of transmission is direct contact between the patient and an infected or carrier person, who may be a visitor, another patient or healthcare staff. The contact can be direct person-person or through some intermediate object.

Another important route of transmission is aerosol sprays, small airborne fluid particles. These pathogen-carrying droplets are expelled by the carrier person when coughing, sneezing or even speaking, and can also be produced during some tests and procedures, for example during a bronchoscopy.

Some pathogens can also become airborne via dry particles that are small enough to be suspended in the air for some time, for example dust particles. Through this route, pathogens can be transmitted over greater distances using air currents, which is why in some health facilities special filters are used in ventilation systems. Some pathogens that are transmitted in this way are legionella, Mycobacterium tuberculosis and the varicella and rubella viruses.

Other routes of transmission are food, water or animal vectors, for example mosquitoes, although they are less common in nosocomial infections.

Some medical procedures tend to be associated with nosocomial infections more frequently than others, for example, catheter implantation and other invasive techniques.

Among the most common pathogens, the following stand out:

  • Staphylococcus aureus
  • S. aureus methicillin resistant
  • Candida albicans
  • Pseudomonas aeruginosa
  • Acinetobacter baumannii
  • Stenotrophomonas maltophilia
  • Clostridium difficile
  • Escherichia coli
  • Tuberculosis
  • Enterococcus vancomycin resistant
  • legionella (Legionnaire's disease, Pontiac fever)


Nosocomial infections can be very serious, both due to the patient's conditions and the strains that cause the infection, many times resistant bacteria that cause infections that are difficult to treatespecially in the respiratory and urinary systems.

The best known bacteria in hospital infections are MRSA or Staphylococcus aureus methicillin resistant (gram positive) and the Acinetobacter baumannii (gram negative). There is an effective treatment for MRSA, but there are few effective drugs for Acinetobacter, a bacterium of which there are also more and more cases of resistance to antibiotics and more cases of hospital infections.

They also seem to increase infections and resistance by resistant strains of Kelsiella pneumoniae causing severe forms of respiratory and urinary tract infections.


Approximately one third of nosocomial infections are considered avoidable or preventable through the implementation of standardized quality control systems and proper hygiene and sterilization protocolsboth in the treatment and management of medical equipment and facilities.

The main prevention measures also include basic protocol practices of health personnel, such as the use of masks, gloves or wash hands with alcohol or bactericidal soap before and after caring for each patient.

The alcohol vapor in carbon dioxide systems (NAV-CO2 system) is one of the most widely used antisepsis systems for healthcare facilities and ventilation systems. It is effective against MRSA, enterobacteria and viruses such as influenza. The hydrogen peroxide vapor has also shown effectiveness against endospore-forming bacteria, such as Clostridium difficile. Also used ultraviolet radiation as a method of sanitizing rooms and surfaces.

Hospitals usually also have protocols and prevention measures that affect visitors and companions of patients. Following these protocols by visitors is important not only to prevent their own infection, but also to prevent the transmission of hospital pathogens to the community.

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