Nosocomial Infection

Nosocomial infections (NI) - also called hospital-acquired infections (HAI) - occur when patients acquire an infection from the healthcare environment within two to three days of entering the hospital (Vincent, 2003). (The etymology derives from "Nosokomiakos", meaning "of the hospital") Nosocomial infections - there are many kinds - can cause complications in the treatment of already sick patients. According to WHO estimates, around 15% of patients under medical care suffer from nosocomial infections, worldwide. And the risk of a patient developing a nosocomial infection has greatly increased in the last decade. It is estimated that 1.7 million such infections occur in the US every year.


The biggest source of potential infection in healthcare facilities are people - both patients and healthcare workers. Human skin contains surface microorganisms on the order of 100 to 10000 per square centimeter. Despite efforts at disinfection and sanitation, there is no such thing as a sterile operating room if there are people in the room. Most of those microogranisms are vegetative bacteria and benign.

Viruses, bacteria and fungal parasites can all cause nosocomial infections. The most common bacterial species that have been isolated from frequently occurring NIs include Staphylococci (especially methicillin-resistant S. aureus, MRSA), Pseudomonas species, Acinetobacter species and members of Enterobacteriaceae family (including Escherichia coli and Klebsiella pneumonia). Most of these gram-positive and negative bacteria are antibiotic resistant and can quickly spread to immunocompromised patients, especially ones that are critically ill. This is why intensive care units (ICUs) see a lot of NIs (Asensio et al., 2000). It has been estimated that around 70% of all nosocomial infections are caused by any of the above-mentioned bacterial species (Chambers, 2005). Nosocomial infections may cause respiratory, eye, gastrointestinal diseases, and more.

Many nosocomial infections are caused by endogenous bacterial populations - i.e. bacteria already in the patient’s body that is moved to another part of the body it shouldn’t be in. Critically ill patients are more prone to colonization with resistant pathogenic strains from the healthcare environment.


Disease is often transferred through contaminated hospital equipment and apparatus. For instance, nosocomial pneumonia is acquired when patients use ventilators which have not been disinfected; bloodstream infections are associated with intravascular devices, and UTIs have been found to be associated with the use of infected catheters (Richards et al., 2000).

  • By blood - transfusion, injection. Accidental sticks by sharps.
  • By direct contact - from caregiver to patient, indirect contact (e.g. secretions from one patient to another patient via hands)
  • By droplets - Two kinds of droplet transmission: (1) when droplets are large and do not remain suspended in air for a long time. Patient picks up disease from touching equipment. This is probably the most common source of nosocomial infection. (2) fine aerosols when droplets can remain in air and transfet from others in hospital (patients or otherwise) to new patient.

The most important determinants of infection are the nature and number of the infectious agents.

Illnesses caused

The most common nosocomial infections include pneumonia, bloodstream infection (sepsis or septicemia), surgical site infections, and urinary tract infections (UTIs).

UTIs account for around 40% of nosocomial infections, while nosocomial pneumonia accounts for 25% of NIs (Lockhart et al., 2007). Surgical site infections account for 17% of all healthcare-associated infections (Napolitano, 2010). Apart from the role of contaminated medical equipment in the spread of these infections, health-care workers can deliver infections to patients inadvertently. These include physicians, nurses, respiratory therapists, radiology technicians, electrocardiogram technicians, housekeepers, paramedics, research assistants and security personnel who unknowingly serve as vectors in the transmission of infection from one patient to another. Many incidents of nosocomial transmission of respiratory ailments such as severe acute respiratory syndrome (SARS) and other infections have been reported to be transferred through these routes (Webb et al., 2004; Kwok et al., 2007).

Common pathogens at healthcare facilities include:

  • Bacillus anthracis
  • Brucella spp.
  • Campylobacterspp.
  • Rochalimaea hensalae
  • Clostridium difficile
  • Listeria monocytogenes
  • Pasteurella spp.
  • Yersinia pestis
  • Salmonella spp.
  • Shigella spp.
  • Clostridium tetani
  • Mycobacterium spp
  • Cryptosporidia spp.
  • Giardia lamblia
  • Toxoplasma gondii
  • Leptospira interrogans
  • Borrelia burgdiferi
  • Chlamydia psittaci
  • Coxiella burnetii
  • Lyssavirus
  • Herpesvirus

Impact and Prevention

nosocomial transmission Nosocomial infections lead to prolonged hospital stays, extensive use of medicine, possible disability, and economic burdens. That’s why medical and safety professionals are concerned about instituting preventive measures to minimize the infection rate. Hygienists, nurses, and others concerned with public health have found that to prevent the spread of nosocomial illnesses, it is necessary to prevent the mechanical and physical transmission of infection inside the healthcare facility. Proper storage and disposal of hospital waste reduces the spread of nosocomial infections. One estimate is that around 25% of hospital waste can potentially cause life-threatening infections (Khan et al., 2017), mostly to people at the hospital.

If hospitals use standard operating protocols and universal precautions for infection control and limit the use of antibiotics, they can help reduce the development of microbial resistance and the spread of nosocomial infections (Khan et al., 2017). Moving very sick patients with contagious diseases away from other patients is a sensible precaution. Hospitals sometimes impose "isolation" in which patients are kept away from others to prevent transmission.

The SOPs for infection control include frequent hand washing by health care workers. Hand washing is considered the simplest and most important intervention in infection control. Use of masks, gloves, and gowns can also help prevent the spread of nosocomial infections (Saloojee, and Steenhoff 2001). Further, proper ventilation of rooms, cleaning, and decontamination of wards reduces the risks of nosocomial infections.

See also:

CDC on Healthcare-Associated Infections
William A Rutaia on HAIs


Agaba, P., Tumukunde, J., Tindimwebwa, J., & Kwizera, A. (2017). Nosocomial bacterial infections and their antimicrobial susceptibility patterns among patients in Ugandan intensive care units: a cross sectional study. BMC research notes, 10(1), 349. doi:10.1186/s13104-017-2695-5
Asensio, A., Oliver, A., González-Diego, P., Baquero, F., Perez-Diaz, J. C., Ros, P., . . . Cantón, R. (2000). Outbreak of a multiresistant Klebsiella pneumoniae strain in an intensive care unit: antibiotic use as risk factor for colonization and infection. Clinical Infectious Diseases, 30(1), 55-60
Chambers, H. F. (2005). Community-associated MRSA—resistance and virulence converge: Mass Medical Soc.
Khan, H. A., Baig, F. K., & Mehboob, R. (2017). Nosocomial infections: Epidemiology, prevention, control and surveillance. Asian Pacific Journal of Tropical Biomedicine, 7(5), 478-482. doi:
Kwok, K. O., Leung, G. M., Lam, W. Y., & Riley, S. (2006). Using models to identify routes of nosocomial infection: a large hospital outbreak of SARS in Hong Kong.
Proceedings. Biological sciences, 274(1610), 611–617. doi:10.1098/rspb.2006.0026
Lockhart, S. R., Abramson, M. A., Beekmann, S. E., Gallagher, G., Riedel, S., Diekema, D. J., . . . Doern, G. V. (2007). Antimicrobial resistance among Gram-negative bacilli causing infections in intensive care unit patients in the United States between 1993 and 2004. Journal of clinical microbiology, 45(10), 3352-3359.
Richards, M. J., Edwards, J. R., Culver, D. H., Gaynes, R. P., & System, N. N. I. S. (2000). Nosocomial infections in combined medical-surgical intensive care units in the United States. Infection Control & Hospital Epidemiology, 21(8), 510-515.
Napolitano, L. M. (2010). Perspectives in surgical infections: what does the future hold? Surgical infections, 11(2), 111-123.
Saloojee, H., & Steenhoff, A. (2001). The health professional's role in preventing nosocomial infections. Postgraduate medical journal, 77(903), 16-19
Vincent, J.-L. (2003). Nosocomial infections in adult intensive-care units. The Lancet, 361(9374), 2068-2077.
Webb G.F, Blaser M.J, Zhu H.P, Ardal S, Wu J.H. Critical role of nosocomial transmission in the Toronto SARS outbreak. Math. Biosci. Eng. 2004;1:1–13

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