Hospital acquired infection : Definition and Causes

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wash your hands to prevent Hospital acquired infections

Hospital-acquired infection, Hospital infection or nosocomial infection is a term applied to infections occurring in hospitalized patients who were neither infected nor were in incubation at the time of their admission to the hospital. About 5% of hospitalized patients suffer from nosocomial infection. Nosocomial infections is an important public health problem and is a major cause of high morbidity, mortality and economic consequences for hospital patients in developing countries like the developed ones today.

The consequences of hospital infections are severe. Patient may require longer hospital therapy, re-entry or even further surgery, increased absent-duty time and the use of community and hospital resources.

The recent move towards shorter hospital stays indicates that the population has more patients with hospital-acquired infections. Furthermore, as the intravenous medication administration becomes increasingly common at home, cannula-related infections may occur in the community once confined to patients in the hospital.

What are the Sources of Hospital acquired infection?

There are two sources of hospital-acquired infections: Exogenous and Endogenous.

Exogenous infection

This is most the important and occurs mostly from

  • Another patient
  • A medical and paramedical personnel harbouring pathogenic agents
  • From the environment.

Endogenous infection

This is due to the presence of body’s normal flora. These flora microorganisms can cause infections in the patient’s different tissues during surgery operations, instrumental manipulation, or nursing procedures.

What are the factors Affecting Hospital-Acquired Infections?

Factors such as Age,Immune status, wound or devices used,virulence of the causing agent greatly influnces Hospital acquired infections
Factors influencing Hospital acquired infections

Hospital acquired infection as a group differ from other community acquired infections, both in their patient profile and the severity and treatment of the disease caused by them. The factors influencing hospital-acquired infections are as follows:

Hospitalized patients

One of the many factors causing hospital-acquired infections is susceptible hospitalized patients. That is because most patients admitted to hospitals have impaired immunity either as part of their previous disease or in some cases as a result of hospital treatment. They are therefore highly susceptible to infection.

Hospital environment

The environment in the hospital has an increasing number of microorganisms due to the large number of infected patients visiting the hospital. In some cases, these microorganisms can infect the sensitive hosts through fomites and other human carriers. Food, water and air contamination have also, in a couple of cases, been involved in hospital outbreaks.

Antibiotics resistance

The infectious agents in the hospital environment are doubtful, also because they are generally resistant to a variety of commonly used drugs. The initial resistant strains of the bacteria are present in large numbers due to the constant pressure of selection, which is exerted because of the necessary antibiotic uses in the hospitals.

Diagnostic or therapeutic procedures

Intravenous and/or urethral catheter insertion, diagnostic or therapeutic interventions may introduce infection to susceptible patient and cause iatrogenic infection.


Blood transfusion, intravenous and blood products may transmit blood-borne pathogens to hospitalized patients if not properly screened. In some cases, the susceptible hosts are fomite medium and other carriers are human. Food and water contamination and, in a few instances, air has also been involved in clinical outbreaks.

Microorganisms Causing Hospital Acquired Infection

Initially most of the hospital outbreaks have occurred as a significant cause of these infections, but are mainly due to Gram-positive organisms such as the Streptococcus pyogenes and Staphylococcus aureus (MRSA) methicillin-resistants’ (STRs).

Pseudomonas and Acinetobacter species are also common nosocomial pathogens because they are extremely resistant and resistant to most commonly used antibiotics, which they can survive as saprophytes in the environment and sometimes even grow within disinfectant solutions bottles.

The fact that MRSA has been carried out in particular on long-term care facilities, such as hospitals, is a cause for serious health issues within the community, also concerns that these organisms may be distributed from hospitals to the general community.

Nosocomial infection Causative organisms
Infection of the urinary tract (catheterization related) Escherichia coli, Klebsiella spp., Enterobacter spp., Serratia spp., Proteus spp., Pseudomonas spp., Enterococcus faecalis, Candida spp., Staphylococcus epidermidis, and other coagulase negative staphylococci
Respiratory infection (aspiration of the fan in comatose patients, etc.) Klebsiella spp., Enterobacter spp., Staphylococcus aureus, Escherichia coli, Pseudomonas spp., Acinetobacter spp., Proteus spp., and Legionella pneumophila
Wound infection (burns, postoperative, diabetic foot, etc.) Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter spp., coagulase-negative staphylococci, Escherichia coli, Proteus spp., Enterococcus faecalis, and Streptococcus pyogenes
Infection with the gastrointestinal tract (food poisoning, infected personnel or patients ‘ transmission). Salmonella spp., Shigella flexneri, Shigella dysenteriae, Shigella sonnei, and Escherichia coli (in children and neonates)

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