In this article we will discuss about Hospital Acquired Infections:- 1. Meaning of Hospital Acquired Infections 2. Factors Influencing Hospital Acquired Infections 3. Sources 4. Mode of Transmission.
Meaning of Hospital Acquired Infections:
Since antiquity, the hospitals were regarded as source of infections to patients after admission. There was necessity to isolate patients with infectious diseases and it was a great success to bring a dramatic reduction in infection rate by the introduction of hand washing with chlorinated lime.
Surgeon Joseph Lister introduced (1865) his antiseptic surgery by the use of carbolic acid. After discovery of pathogenic bacteria in the early 20th century, Str. pyogenes infection in burn and post-operative infection has become important. In a survey by WHO (1992) the prevalence of hospital acquired infection was reported as 3-21% with a mean of 8.4%. The hospital infections have a mortality of about 1%.
Hospital acquired infections are also called as nosocomial infections (from nosocomion, meaning hospital) are defined as infections developing in patients after admission to the hospital. The infection may manifest during their stay in the hospital or after the patient is discharged.
Factors Influencing Hospital Acquired Infections:
1. Age:
Neonates and elderly of extreme ages may acquire hospital infection because of their long stay in hospitals and inefficient immunity.
2. Infected Patients:
Patient with community acquired or non-hospital infection due to pathogenic microorganisms may enter the hospital and spread the infection to close contents (susceptible patients and attending staff).
3. Drug Resistance:
The drug resistant organisms (Coliforms, and Staph, aureus) may show increased virulence or transmissibility as well as limiting the choice of therapy.
4. Susceptible Patients:
Hospitalized patients with pre-existing diseases (diabetes, immunosuppression, patients in special care units or with prosthetic implants are at risk and more susceptible to hospital infections. Groups of microorganisms previously regarded as non-pathogenic have now emerged as pathogens. These opportunistic organisms are Staph, epidermidis, viridans streptococci.
5. Surgical Procedures:
The natural defence mechanisms of the body surface may be bypassed by injury or by a diagnostic or therapeutic intervention such as insertion of a urethral or intravenous catheters. These are iatrogenic infections.
Sources of Hospital Acquired Infections:
A. Endogenous:
Many opportunistic infections are caused by the patients own flora “which are not pathogenic under normal conditions but only when there is underlying disease”. This is called as auto-infection or autochthonous infection.
B. Exogenous:
Hospital infection is mostly exogenous from other people or immediate objects in the environment.
Exogenous Sources:
1. Contact with other Patients or Staff:
Besides patients and hospital personnel suffering from infections or asymptomatic carriers, people are more important sources or reservoirs.
2. Environmental sources are inanimate objects, air, water, and food in the hospital.
(a) Inanimate Objects:
Bedpans, urinals, light, table, blankets, medical equipment’s (endoscopes, catheters, needles, spatula, and other instruments), floor, food, water (contaminated by kitchen and other hospital staff or visitor). Coliforms are most common in moist environment (fluids in which they can survive for long time and sometimes multiply).
(b) Hospital Air:
Hospital over-crowding is responsible for an increase in the bacterial count in the hospital air. Hospital air harbours Gram-positive bacteria.
(c) Surface:
Surfaces contaminated by patient’s excretions, secretions, blood, and body fluids, animals, insects are sources of hospital infections.
Mode of Transmission of Hospital Acquired Infections:
There are four main routes of infections:
1. Contact Route is the Principal Means of Transmission of Hospital Acquired Pathogens.
(a) Hands or clothing’s of hospital staff may get contaminated by microorganisms from their own body or other patients. The important vehicle of transmission of hospital infection is the hand of hospital staff. Staph, aureus, Str. pyogenes, Esch. coli, Klebsiella, and Candida albicans are spread by hand contact. The hand washing by hospital personnel is a significant contribution to control the nosocomial infections.
If patients susceptible to infection are housed in the same ward where the same staff looks after both infected and non-infected patients, there is a great chance of transmission of microorganisms from one person to another by direct contact of hands and clothing’s of the same hospital personnel.
(b) Inanimate objects are reservoirs of pathogenic bacteria which may spread without increasing their numbers, but Ps. aeruginosa may multiply in moisture and enhance the risk of infection.
Certain instruments (endoscope, bronchoscope, cytoscope) are difficult to be sterilised because they do not withstand heating; if they are not properly sterilised or disinfected, there is possibility of transmission of pathogenic bacteria through these instruments.
2. Airborne Route:
Transmission by Aerial Route may occur by:
(a) Droplet of respiratory infection is transmitted from one person to another by inhalation.
(b) Dust from bedding, floors, exudate, dispersed from a wound during dressing and from the skin from natural shedding of skin scales, spread to the susceptible site e.g. Ps. aeruginosa, Staph, aureus.
(c) Aerosols produced by nebulizers, humidifiers and air-conditioners transmit certain pathogens (Coliforms, Legionella) to the respiratory tract, if water in the instrument becomes contaminated.
(d) Oral Route:
Antibiotic resistant Gram-negative bacilli are mostly found in hospital food. They may not cause gastroenteritis, but they may colonies in the recipient’s intestine and become the faecal flora of these patients.
4. Parenteral Route:
Transmission of infection by parenteral route has become less frequent because of the use of disposable syringe and needle. Certain infections are transmitted by transfusion of contaminated blood. Hepatitis B and HTV infections may be transmitted in this way.