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Nosocomial infections are defined as hospital-acquired infections (i.e., infections or diseases acquired by patients few hours after hospitalization). They can also be referred to as healthcare-associated infections (HAIs). Nosocomial infections are infections or diseases that are contracted from a healthcare environment, clinic facility or hospital (Table 1). HAIs occur from disease-causing microorganisms (pathogens) that develop and spread within a particular healthcare facility or hospital and which are acquired by patients while they remain in the hospital for treatment. Such infections can also have an effect on even visitors to healthcare facilities, and these persons including the patients can serve as probable route by which the pathogen responsible for the HAIs spreads to the community (i.e., the outside environment of the hospital). Other healthcare personnel and healthcare givers and any other person who has contact (directly or indirectly) with the hospital where a nosocomial infection is spreading will also fall victim of the disease. Basically, nosocomial infections are a direct result of the complications of the primary infections or diseases of the hospitalized patients; and this culminates to a secondary infection that are sometimes serious than the principal or primary infection.


Nosocomial infections are different from community-acquired infections – which are infections, that a patient brings from the community to the hospital, and which is already incubating in the patient prior to his or her hospitalization. Long hospitalization of a patient can predispose such a person to contracting a disease/infection he or she did not originally have before being hospitalized. On a worldwide scale, nosocomial infections cause a significant amount of morbidity and mortality in a defined human population, and HAIs are usually caused by bacteria, viruses and fungi. Microorganisms in the algae family rarely cause nosocomial infections. In some cases, nosocomial pathogens are often found attached as normal microflora of both patients and hospital staff. Cross-infection of a nosocomial pathogen (from a hospital staff to a patient) can occur during medical and/or physical examination of the patient, and this usually occurs when proper infection control measures and safety precautions are not fully imbibed by the healthcare worker. Nevertheless, the majority of nosocomial infections are as a result of the presence of some pathogenic bacteria that have adapted to the hospital setting over time.

Table 1. Some nosocomial pathogens and their corresponding infections

HAIsBacterial Pathogens Implicated
Urinary tract infections (UTIs)Pseudomonas aeruginosa Candida species Enterobacter species Escherichia coli Enterococci
Respiratory tract infections (RTIs)Staphylococcus aureus Acinetobacter species Pseudomonas aeruginosa Enterobacter species Klebsiella pneumoniae
BacteraemiaCandida species Staphylococcus aureus Pseudomonas aeruginosa Coagulase Negative Staphylococci(CNS) Enterobacter species Enterococci
Skin infectionsCoagulase Negative Staphylococci(CNS) Staphylococcus aureus Escherichia coli Pseudomonas aeruginosa
Wound infections (e.g. surgical wounds)Escherichia coli Staphylococcus aureus Enterobacter species Escherichia coli Enterococci Coagulase Negative Staphylococci(CNS)

In addition, other inanimate materials or objects such as food, tables, chairs, water systems, staircase handle, beddings and even hospital equipments used directly on the patients can be a considerable source through which patients and non-patients acquire or contract HAI pathogens. Bacteria and fungi are mostly implicated as causative agents of nosocomial infections.

Some of the means by which people acquire a nosocomial infection after a short or long stay in the hospital are as follows:

  1. Presence of surgical wounds, burns or bedsores which compromises the protective functions of the skin thus, exposing it to nosocomial pathogens.
  2. Patient-to-hospital personnel contact which allows transmission of pathogen from patients to hospital staff and vice versa.
  3. Use of hospital devices that has direct contact with the internal environment of the body e.g., catheterization and intubation.  
  4. Relocation of a normal microflora from its resident site in the body to a new location during surgery.
  5. Long stay in an intensive care unit (ICU) or a high dependency unit of a clinic facility.
  6. Breathing in of bacterial or fungal spores from a hospital environment.


Aschengrau A and Seage G.R (2013). Essentials of Epidemiology in Public Health. Third edition. Jones and Bartleh Learning,

Gordis L (2013). Epidemiology. Fifth edition. Saunders Publishers, USA.

Nelson K.E and Williams C (2013). Infectious Disease Epidemiology: Theory and Practice. Third edition. Jones and Bartleh Learning. 

Riedel S (2004). Biological warfare and bioterrorism: a historical overview. BUMC Proceedings, 17:400-406. 

Rothman K.J, Greenland S and Lash T.L (2011). Modern Epidemiology. Third edition. Lippincott Williams and Wilkins, Philadelphia, PA, USA.

Schneider M.J (2011). Introduction to Public Health. Third edition. Jones and Bartlett Publishers, Sudbury, Massachusetts, USA.


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