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Infections in patients requiring ventilation in intensive care: application of a new classification
Alan E. Murray1, John J. Chambers, Hendrik K.F. van Saene
1Department of Medical Microbiology and Anaesthesia, Wirral Hospital NHS Trust, Merseyside, and.
Abstract:
OBJECTIVE: To classify infections according to the carrier state determined by surveillance cultures of throat and rectum, rather than by the traditional criterion of the time of onset after admission. METHODS: An observational cohort study of 3 months' duration was performed in a mixed medical---surgical intensive care unit (ICU) in a district general hospital of a subset of patients requiring mechanical ventilation for 3 days. Surveillance cultures from throat and rectum were obtained on admission to the ICU and then twice weekly to distinguish carriage of potentially pathogenic microorganisms (PPM) brought in by the patient from microorganisms acquired during the ICU stay. RESULTS: Out of the total population of 104 patients, 21 patients were enrolled over 3 months. Eight patients (38%) developed 12 infections, half of which were of primary endogenous pathogenesis and caused by Haemophilus influenzae, Candida albicans and Pseudomonas aeruginosa carried by the patients on admission. The remaining six were of secondary endogenous pathogenesis and caused by Acinetobacter baumannii and Pseudomonas aeruginosa acquired in the unit. CONCLUSIONS: Traditional classifications of hospital infection are challenged. If the traditional 48-h cut-off point was used, then 9 of 12 cases (75%) of infection would have been classified as nosocomial, whereas using the method based on the carrier state, 50% of all infections were caused by microorganisms carried by the patient on admission to the ICU. Moreover, we believe that the distinction between primary endogenous, secondary endogenous and exogenous is valid because these three types of infection each require different control methods.
Insights
Hospital infections can be better classified by patient carrier status than by onset time. This approach reveals that half of infections originate from microorganisms patients carried into the intensive care unit (ICU).
Area of Science:
- Infectious Diseases
- Critical Care Medicine
- Microbiology
Background:
- Traditional classification of hospital-acquired infections relies on the time of onset post-admission.
- This method may misclassify infections originating from microorganisms patients already carry.
- Distinguishing infection sources is crucial for effective control strategies.
Purpose of the Study:
- To classify infections based on the patient's carrier state of potentially pathogenic microorganisms (PPM).
- To compare this carrier-state classification with the traditional time-of-onset criterion.
- To evaluate the validity of distinguishing between primary endogenous, secondary endogenous, and exogenous infections.
Main Methods:
- An observational cohort study was conducted in a mixed medical-surgical intensive care unit (ICU).
- Patients requiring mechanical ventilation for at least 3 days were included.
- Surveillance cultures of throat and rectum were obtained on ICU admission and twice weekly thereafter.
Main Results:
- Of 21 enrolled patients, 8 (38%) developed 12 infections.
- Half of these infections were primary endogenous, caused by PPM carried by patients on admission (e.g., Haemophilus influenzae, Candida albicans, Pseudomonas aeruginosa).
- The other half were secondary endogenous, caused by PPM acquired during the ICU stay (e.g., Acinetobacter baumannii, Pseudomonas aeruginosa).
Conclusions:
- The carrier-state classification challenges traditional hospital infection definitions.
- Using the carrier-state method, 50% of infections were caused by pre-existing microorganisms, compared to 75% classified as nosocomial by the traditional 48-hour cutoff.
- The distinction between primary endogenous, secondary endogenous, and exogenous infections is clinically relevant, requiring tailored control measures.