hospital-acquired infections

What causes hospital-acquired infections?

The development of a nosocomial infection, also known as a healthcare-associated infection, is possible when three elements are present: a subject (the elderly, for example, have a higher susceptibility depending on the co-morbidities they have), an infectious agent and finally a mean of transmission.

The three micro-organisms most frequently responsible for nosocomial infections are Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. It is part of the commensal flora.


There are two possible mechanisms, the so-called endogenous infection and the exogenous infection.

– Endogenous infection concerns patients who infect themselves with their own germs (self-contamination) as a result of an invasive procedure performed during hospitalisation. The reason for this may also be a decline in the patient’s own defences if they are particularly weakened by their condition.

– Exogenous infection is linked to contamination of the hospital environment (water, air, equipment, food).

What factors can increase the risk of contracting an hospital-acquired infection?

Patient-related risk factors:

– Advanced age

– Unfavourable terrain or comorbidities

– Immunosuppression

– Diabetes

– Obesity

Health care-related factors:

– Exposure to an invasive medical device (e.g. vascular catheter)

– Hospital environment and hygiene

Factors related to the infectious agent:

Antibiotic resistance

– Pathogenic germs that grow and secrete toxins in the body.

Finally, nosocomial infections are more frequent in intensive care, surgery, burns and haematology departments.

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