An infection is said to be nosocomial if it appears during or following hospitalization (or outpatient care) and if it was not present or incubated on admission to hospital. This criterion is applicable to any infection. This definition includes both patient and caregiver infections. It does not prejudge either the endogenous or exogenous origin of the microorganism responsible or the avoidable nature of this infection.

When the precise admission situation is not known, a delay of at least 48 hours after admission (or a time longer than the incubation period when it is known) is commonly accepted to distinguish a nosocomial acquisition infection of a community infection. However, it is recommended to assess, in each doubtful case, the plausibility of the causal link between hospitalization and infection.

For surgical site infections, nosocomial infections are defined as occurring within 30 days of surgery or, if a prosthesis or implant is implanted, within one year of surgery. intervention. This duration is also allowed for the follow-up of a childbirth.

Home care practice can also lead to infections. These infections are considered to be care-related when they are not related to a hospital stay or other care organization and developed at least 48 hours after admission to the home care facility.

  1. Definition

  2. Mode of contamination

  3. Causes

  4. Pathogens

  5. Diagnostic

  6. Treatment

  7. Prevention

  8. Infectious risk factors related to the patient


A nosocomial infection is an infection contracted in a health facility. The disease is considered nosocomial if it was absent at the time of admission to the health facility. In addition, it is considered that an infection that occurs at the level of the part operated during surgery is nosocomial if it occurs within thirty days after this operation.

Mode of contamination

Germs are present everywhere in a natural way, especially on the patient and the caregivers. They are also found in food, water, ambient air. They may be present, despite all the precautions, on the care equipment. In fact, these germs are everywhere and not only in the hospital. But by definition, there are many fragile people in these institutions, who are therefore less able to defend themselves against these aggressors.


There are several types of nosocomial infections, with different modes of transmission.

  • Endogenous transmission : the patient is infected with his own germs by an invasive act or a particular ground.

  • Exogenous transmission : infection transmitted by another patient, by hospital staff (by the hands or in contact with medical or paramedical equipment) or related to the environment (water, air, food, etc.).

Some patients are more fragile and will be more easily susceptible to nosocomial infections : elderly patients and newborns, immuno-depressed patients (who have diseases or treatments affecting their defense system such as chemotherapy), burn victims , diabetic patients, patients undergoing antibiotic treatment (which can unbalance the bacterial flora usually present and select resistant bacteria ...).

Invasive procedures such as perfusion, urinary catheters, artificial ventilation or surgery, although necessary for treatment, will also contribute to nosocomial infections.

The most frequently implicated organisms are bacteria : Escherichia coli (germ usually present in the digestive tract), Staphylococcus aureus (germ usually found on the skin and in the nostrils) and Pseudomonas aeruginosa.

The peculiarity of these organisms is that they have often acquired resistance to antibiotics, such as MRSA (methicillin-resistant staphylococcus aureus) or EBLSE (broad-spectrum betalactamase-producing enterobacteria).

The most common nosocomial infections are urinary tract infections, pneumonia, surgical site infections and bacteremia (presence of germ in the blood).


The agents involved are varied: bacteria, fungi, viruses, parasites, NCTA.

Of the bacteria, gram-negative bacilli account for about 60% of the germs encountered, Gram-positive cocci 30%.

The origin of the germ can be exogenous (from another patient, staff, the environment) or endogenous (from the patient himself). Several different mechanisms can therefore lead to a nosocomial infection.

If everything must be done to prevent the occurrence of endogenous infections as exogenous, it is mainly on the latter that the effort of prevention by avoiding the transmission of germs. The prevention of endogenous infections remains more delicate.


The infections contracted most frequently by patients are mostly urinary tract infections. They then come pneumonia, septicemia, and surgical wound infections. The diagnostic approach will consist in identifying the origin and the type of infection, by a clinical and biological examination of the symptoms with the appropriate complementary examinations if necessary.


Nosocomial infections sometimes require an extension of the operation.

The treatment of nosocomial infections uses the same principles as community infections but it is often more difficult because the germs encountered in nosocomial infections have often acquired resistance to antibiotics.

In some cases, especially in surgical site infections, it is necessary to reoperate patients, to drain a postoperative abscess, change an orthopedic prosthesis set up...


It is essential to closely monitor the most exposed services, risk situations and to evaluate the effectiveness of the measures taken.

Preventive measures consist of :

Apply rigorous hygiene measures : hand hygiene, use of hydro-alcoholic solutions.

  • Set up care protocols for the various medical and paramedical procedures.

  • Use sterile or disposable medical equipment.

  • Improve sterilization methods and apply good practices for disinfection of equipment.

  • Detect risk situations and epidemics.

  • Detection of patients carrying multi-resistant germs and implementation of protocols for the management of colonization situations with multidrug-resistant organisms and epidemic situations. Septic and geographical isolation of patients with multi-resistant germs. That is to say isolate patients with multi-resistant germs in single rooms, wearing over-gowns during medical visits or family.

  • Supervision of the prescription of antibiotics and creation of guides of good practices.

The Alert Network was created a decade ago, investigating and monitoring nosocomial infections (RAISIN) which aims to harmonize at the national level nosocomial infection surveillance methods and coordinate actions alert and surveillance.

At the level of the hospital centers, it is the mission of the CLIN (Committees against Nosocomial Infections) and EOHH (Operational Teams in Hospital Hygiene) made up of prevention professionals, medical and non-medical, in charge of implementing prevention, surveillance, reporting, evaluation and training activities in the institution.

Infectious risk factors related to the patient

The presence in patients of certain characteristics increases, sometimes very importantly, their risk of acquiring a nosocomial infection :

1. Chronic pathologies

  • Diabetes

  • Renal failure

  • Hepatic insufficiency

  • Incontinence (major factor of urinary tract infections)

  • Immunodepression (aplasia, leukopenia, leukemia, cancer, AIDS)

2. Certain acute pathologies motivating hospitalization

  • Polytrauma

  • Burns

  • Acute visceral failure

3. Disturbed nutritional status
Undernutrition is an important factor for all infection sites and obesity promotes postoperative parietal abscesses.

4. The age
Before one year and after age 65, the risk of infection is always increased.

Other factors are established in the pathogenesis of different localizations of nosocomial infection or in particular situations (maternity for example).


  • Technical Guide for Hospital Hygiene, NOSOCOMIAL INFECTION : DEFINITION, FREQUENCY AND RISK, C.CLIN Southeast - Sheet n° 2.01, 2004, p 5.

  • Jeff, Journal of Women Health (, Nosocomial infections - Causes, diagnosis and prevention.

  • Le Figaro Santé (, Infectious Disease - Nosocomial Infection.