Updated 13 February 2013

Hospital Acquired Infections

Hospital acquired infections are those acquired in a health care institution. Most infections diagnosed after 48 hours of hospitalisation are considered to be hospital acquired.


  • Hospital acquired infections (HAIs) are those that patients acquire in a health care institution.
  • HAIs increase patient fatality rates, the risk of acquiring other infections, and length of stay in hospital, thus also increasing health care costs.
  • HAIs may be caused by viruses, bacteria or fungi, and most commonly affect the urinary tract, respiratory tract, wounds and blood.
  • The organisms causing HAI are often resistant to numerous antibiotics.
  • Basic hygiene measures such as hand-washing and sterile equipment can help reduce the incidence of HAIs.

What are hospital acquired infections?

Sometimes, an infection that is diagnosed even after a patient has been discharged can be considered ‘hospital acquired’ if it can be traced back to the hospital stay. For example, a wound infection that only develops after discharge from hospital would still be regarded as a nosocomial infection.

HAIs greatly increase patient fatality rates, the risk of patients acquiring other infections, and length of stay in hospital, therefore also increasing health care costs.

Types of hospital acquired infections
HAIs may be caused by viruses, bacteria or fungi. They can affect different parts of the body, most commonly the urinary tract, the respiratory tract, wounds and the blood.

Organisms that commonly cause urinary tract infections and pneumonia in the hospital are the Gram negative bacilli – a group of organisms that includes E. coli, Klebsiella spp, Pseudomonas aeruginosa and Acinetobacter baumanii.

Wound infections are most often caused by Staphylococcus aureus, although sometimes Gram negative bacilli can also be involved.

Bloodstream infections can be caused by a wide variety of organisms, including yeasts (e.g. Candida albicans). The most common organisms causing bloodstream infection vary from hospital to hospital, but include E. coli, S. aureus, Klebsiella, Enterobacter and Candida albicans.

Increased resistance to antibiotics
Antibiotics (antibacterials) are a powerful tool for fighting bacterial infection. However, a feature of HAIs is that the organisms causing HAI are often resistant to numerous antibiotics. Organisms in the hospital environment are exposed to many different antibiotics, and multi-drug resistant bacteria are now common in many hospitals. In some instances, the organisms causing HAIs are resistant to all available antibiotics. This is fortunately still rare, but is still cause for great concern.

Risk factors for hospital acquired infections
The following factors increase risk for HAIs:

Certain invasive medical procedures, such as intubation, urinary catheters and intravenous lines (drips) increase the risk of hospital acquired pneumonia, urinary tract infection and bloodstream infection, respectively.

Patients who have had surgical procedures are obviously at risk of wound sepsis. The nature and extent of the surgery can affect the risk of developing wound sepsis – surgery that involves cutting through an infected area would be at higher risk of post-operative wound infection.

Patients with burns are also at risk of infection of the burn wound, and great care is taken to keep the wounds as clean as possible while they heal.

Poor hospital organization, which may include factors such as contaminated water and air conditioning systems, staff shortages, poor hospital layout e.g. beds too close to each other, and staff failing to follow hygiene and safety precautions such as hand-washing and adequate sterilization of equipment.

The severity of the patient’s illness, state of the immune system, and length of stay in hospital. The elderly and children are also generally more vulnerable to HAIs.

Treatment of hospital acquired infections
There are many effective treatments available for HAIs; the exact type of treatment will depend on the type of pathogen and the nature and severity of the infection. Generally, any inserted tubes are removed, if these are suspected to be causing the problem, and antifungal, antibiotic or antiviral medication is given.

Can hospital acquired infections be prevented?
There is no way to eliminate the risk of hospital-acquired infections completely. However, the following measures by hospital staff and patients themselves can help to reduce the incidence of HAIs:

  • Following correct hygiene procedures e.g. Correct hand washing and use of alcohol hand-rubs, proper disposal of body fluids, and providing a clean health-care environment and sterile medical equipment.
  • Hospital visitors should respect any restrictions e.g. on numbers of visitors, not sitting on patient’s beds etc. Visitors should also follow basic hygiene precautions such as hand-washing before and after visiting, and should stay at home if they themselves have an infection.
  • As the risk of acquiring an infection increases the longer a patient stays in hospital, patients should be encouraged to get up, have any intravenous lines and urinary catheters removed and go home as soon as it is medically advisable.
  • To help prevent the proliferation of antibiotic resistant bacteria, doctors should be cautious about over-prescription. The full course of medication prescribed must be completed. If a patient does not complete a course of antibiotics, then some bacteria may survive and develop into a new, drug-resistant strain.

How common are HAIs?
In developed countries, about 5 to 10% of patients admitted to acute care hospitals acquire an infection which was not present or incubating on admission. The rate for developing countries can exceed 25%. The statistics for South Africa probably fall somewhere in between these numbers. Unfortunately there are no good, large scale surveys of nosocomial infection rates in South Africa.

Reviewed by Dr Andrew Whitelaw, Department of Microbiology, University of Cape Town

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