The factors which contribute to the development of hospital infection are the relationship between the agent, the host (patient), and the environment.
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It is essential to understand this relationship for the success of any hospital infection control programme. The methods, process, policies and procedures adopted in day-to-day patient care have a very significant relationship to these factors.
Source of Infection:
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1. In a closed environment where many medical and paramedical personnel are in close attendance on patients in various stages of disability, it becomes very difficult to pinpoint the source of infection.
The infection can be acquired as a cross-infection from other patients, from hospital personnel medical, nursing and paramedical, and visitors.
2. The second source is the hospital’s inanimate environment, independent of human contamination. The inanimate environment of the hospital provides for multiple drug-resistant bacteria.
It also provides the means of transmitting microorganisms responsible for many epidemic nosocomial infections. In environmental infection, almost everything that comes in contact with the patient-bathroom and toilet fixtures, hospital furniture, crockery, linen, bedding, bedpans, etc.—are all capable of being the source of infection.
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3. The third source is self-infection from microbes that were carried from outside by the patient on admission to the hospital but invaded his or her tissues subsequently, often as a consequence of a procedure performed in the hospital.
4. The Agent: Almost the entire spectrum of microbes from bacteria to viruses, fungi and protozoa have been incriminated in hospital infections, starting from the conventional pathogens that cause disease in normal persons in the absence of specific immunity, (e.g. Staphylococcus aureus, group “A” streptococci and Salmonella), to the conditional pathogens (e.g. Pseudomonas, Proteus), and opportunistic pathogens that cause generalised disease in patients with dimished body resistance (e.g. fungi such as Candida, Nocardia, Aspergillus).
Nearly 25 to 50 per cent of all hospital infections have been found to be due to gram-negative organisms, and up to 10 per cent of the infections are contributed by staphylococci.
Staphylococcus aureus is one of the most important agents which produce unrelated forms of disease, from a variety of septic lesions to acute gastroenteritis.
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Pseudomonas has been generally responsible for secondary infection in burns, wounds and urinary tract infection. Escherichia coli have been found to be responsible for catheter-associated urinary tract infections.
Salmonella is introduced in hospitals through food items by carriers and spread by faecal contamination.