Supplemental Lecture (98/05/09 update) by Stephen T. Abedon (firstname.lastname@example.org)
These three factors lead not just to a higher likelihood of transmission of pathogens within hospitals, but potentially to an evolution of enhanced disease -causing potential among microorganisms present within hospitals.
Presence of pathogens
- Chapter title: Nosocomial Infections
- A list of vocabulary words is found toward the end of this document
- Nosocomial [hospital acquired] infections
- Nosocomial infections are those that originate or occur in a hospital or hospital-like setting.
- Big problem:
- Nosocomial infections are responsible for about 20,000 deaths in the U.S. per year.
- Aprpoximately 10% of American hospital patients (about 2 million every year) acquire a clinically significant nosocomial infection.
- Reasons problem exists:
- Nosocomial infections are the result of three factors occurring in tandem:
- high prevalence of pathogens
- high prevalence of compromised hosts
- efficient mechanisms of transmission from patient to patient*
- *this is also known as chains of transmission .
- Nosocomial infections are primarily caused by opportunists , particularly by:
- Enterococcus spp.
- Escherichia coli
- Pseudomonas spp.
- Staphylococcus aureus
- "The sites of nosocomial infctions, in order from most to least common, are as follows:
- urinary tract
- surgical wounds
- respiratory tract
- skin (especially burns)
- blood (bacteremia)
- gastrointestinal tract
- central nervous system
- (p. 439, Black, 1996)
- These microorganisms tend to acquire antibiotic resistance factors .
- Normal flora:
- These pathogens also tend to become incorporated into the normal flora of hospital workers
- Nosocomially acquired, opportunistic infections thus tend to be both:
- very available for transmission to patients
- and not easily treated once infections are under way
Chain of transmission
- Broken skin and mucous membranes:
- Patients tend to be susceptible to infection because they display broken skin or mucous membranes (wounds).
- This is regardless of whether the wounds are acquired in the hospital or in an accident resulting in their admission to a hospital.
- In addition, many patients are immunodepressed .
- Thus, their immune systems are less able to fight off infections once acquired.
- Again, this is either because of something done to them in the hospital or for reasons associated with why they entered the hospital.
- Many sick under one roof:
- The purpose of a hospital is to gather together the sick and injured into one place in order to efficiently transmit pathogens to and between them . . .
- Well, not exactly, though there are a number of routes of transmission that are made much more efficient by the same means that make it more efficient to treat patients in hospitals, rather than treating them in their homes.
- Particulary, the movement of pathogens from individual to individual via various routes is referred to as chains of transmission.
- A good example of how chains of transmission can get completely out of hand is childbirth fever during the 19th century. Here doctors moved between patients without washing hands between. Worse, they moved between autopsies of individuals who had succumbed from childbirth fever to birthing women, again without washing hands in between.
- More subtle transmission:
- Today things are a lot more subtle.
- Transmission now is generally a consequence of either accidental or deliberate disregard of established protocols designed to minimize transmission between patients or from hospital workers to patients.
- "Theoretically, nosocomial infections can be transmitted by all modes of transmission that occur in the community. However, direct person-to-person transmission between an infected patient, staff member, or visitor and noninfected patients; indirect transmission through equipment, supplies, and hospital procedures; and transmission through air are most common in hospitals." (p. 438, Black, 1996)
- A set of procedures and guidelines designed to both prevent the infection of the health care worker and to break chains of transmission are together referred to as the universal precautions.
- In particular these procudures are employed to prevent the transmission of blood (and other body fluid)-borne pathogens such as HIV and hepatitis B virus. However, faithful following of these procedures will interfere with the trasmission of most pathogens.
- "Universal Precautions apply to the following body fluids: blood, semen, and vaginal, tissue, cerebrospinal, synovial (joint cavity), pleural, peritoneal, pericardial, and amniotic fluids. The CDC has stated that Universal Precautions do not apply to feces, nasal secretions, sputum, sweat, tears, urine, and vomitus, as long as these do not contain visible blood. This is not to imply that no viruses are present in these fluids but rather that the risk of transmission is either very low or unproved." (p. 439, Black, 1996)
Preventing nosocomial infections
- should avoid direct contact with patients, fomites, or, especially, body fluids
- should wear barriers such as gloves when contact is necessary or expected
- should avoid puncturing oneself with anything and therefore should minimize exposure to sharp instruments, especially body fluid-contaminated sharp instruments
- should not expose patients to the body fluids (or substances, e.g., "weeping dermatitis") of others, such as that of health care workers
- Methods of prevention of nosocomial infection (and breaking the chain of transmission ) include:
- observance of aseptic technique
- frequent hand washing especially between patients
- careful handling, cleaning, and disinfection of fomites
- where possible use of single-use disposable items
- patient isolation
- avoidance where possible of medical procedures that can lead with high probability to nosocomial infection
- various institutional methods such as air filtration within the hospital
- general awareness that prevention of nosocomial infection requires constant personal surveillance
- active oversight within the hospital
- Chain of transmission
- Nosocomial infections
- Preventing nosocomial infections
- Universal precautions
Practice question answers
- "The interaction of . . . three principal factors contributes to nosocomial infections." (p. 378, Tortora et al., 1996) Note that I am not looking for specific details about how nosocomial infections occur and do or do not propagate. Instead I am looking for three established parameters (generalities) which, together, lead to nosocomial infections being likely, frequent, and a problem for hospitals. [PEEK]
- More than anything else, what in general contributes to the transmission of pathogens within hospitals (I am looking for an answer other than or more specific than "doctors, nurses, and other health care workers")?[PEEK]
- List five methods through which chains of transmission of pathogens within hospitals may be broken. [PEEK]
- What three general categories of factors come together in hospitals which result in nosocomial infections being more prevalent per hospitalized individuals than are infections acquired outside of hospitals (i.e., per nonhospitalized individual)? [PEEK]
- Give two reasons (i.e., conditions of health) for why hospital patients tend to be more susceptible to nosocomial infections than the general populace. I'm looking for properties of the patients rather than aspects of hospitals (i.e., not "chains of transmission") or pathogens (i.e., not "presence of pathogens"). [PEEK]
- Universal precautions are specifically a means of avoiding the transmission of what? [PEEK]
- The Universal Precautions were initially developed specifically to prevent the transmission of what? [PEEK]
- Name the three factors that together are responsible for the high incidence of nosocomial infections. [PEEK]
- Name three procedures or policies that can serve to minimize the occurrence of nosocomial infections. [PEEK]
- (i) prevalence of pathogens, (ii) prevalence of compromised hosts, (iii) efficient mechanisms of transfer
- accidental or deliberate disregard for established protocols designed to inhibit transmission.
- (i) observance of aseptic technique; (ii) frequent washing of hands especially between patients; (iii) careful handling, cleaning, and disinfection of fomites; (iv) where possible use of single use disposable items; (v) patient isolation; (vi) avoidance where possible of medical procedures that can lead to nosocomial infection with high probability; (vii) various institutional methods such as air filtration within the hospital; (viii) general awareness that prevention of nosocomial infection requires constant personal surveillance; (ix) active oversight within the hospital.
- presence of pathogens, compromised hosts, chain of transmission.
- previously sick so at risk for secondary infections, subject to surgical wounding, some accident victims, HIV infected, undergoing anti-cancer chemotherapy, recipients of organ transplant so on immune system suppressing drugs
- blood-borne pathogens; hepatitis B virus; HIV
- blood-borne pathogens
- prevalence of pathogens, susceptible hosts, chains of transmission
- observance of aseptic technique; frequent hand washing especially between patients; careful handling, cleaning, and disinfecting of fomites; use of single-use disposable items where possible; patient isolation; avoidance where possible of medical procedures that can lead with high probability to nosocomial infection; various institutional methods such as air filtration within the hospital; general awareness that prevention of nosocomial infection requires constant personal surveillance; active oversight within the hospital
- Black, J.G. (1996). Microbiology. Principles and Applications. Third Edition. Prentice Hall. Upper Saddle River, New Jersey. pp. 436-443.
- Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA, pp. 373-382.