Colonization, infection and dissemination in intensive care patients

Nosocomial infections are a substantial problem in hospitals all over the world and the incidence is among the highest in the intensive care unit, affecting mortality and morbidity for the individual patient and cost for the society. In order to prevent these infections it is important to gain knowledge about colonization and infection pathways as well as about bacterial dissemination between patients.

The overall aim of the present study was to investigate bacterial and fungal colonization pattern, dissemination pattern within and between patients and the incidence of some ICU-acquired infections in intensive care patients, treated in a multidisciplinary Swedish university hospital ICU. Colonization and dissemination patterns of microorganisms were studied by microbiological analyses and antimicrobial susceptibility was monitored over time. Subtyping was performed by using phenotyping as well as genotyping methods, such as the Phene-Plate system and PFGE (pulse-field gel-electrophoresis). Fungal colonization index and other risk factors for acquiring invasive candida infection, were studied in patients with a length of stay of at least seven days. In addition, the status of the immunosystem was monitored with HLA-DR expression once a week in these patients.

The main results and conclusions of this thesis can be summarized as:

* Intubated intensive care patients are often heavily colonized in the lower airways with potentially pathogenic microorganisms, aerobic and anaerobic bacteria as well as yeasts.

* Different colonization routes were demonstrated for different species; primary colonization of the oropharynx or concomitantly in the lower airways, was shown for Staphylococcus, Enterococcus, Enterobacteriaceae and Candida spp., while Pseudomonas and other non-fermenting gram-negative rods and several anaerobic species often showed primary colonization of the trachea.

* The dissemination rate of CoNS between ICU patients was high, 70% of patients treated for more than three days were involved in at least one transmission event.

* Prolonged ICU stay was correlated to an increased rate of cross-transmission between patients as well as a significantly higher risk of being colonized with multi-resistant strains.

* The diversity of colonizing CoNS was significantly decreased in ICU patients with a length of stay of at least five days.

* The endogenous spreading of resistant clones within patient’s skin and mucosal areas increased with time.

* The incidence of invasive candida infections was high in the ICU patient population studied, despite a frequent use of antifungal agents. This was probably due to that the majority of the patients were burdened by several risk factors.

* High colonization index (≥ 0.8) and recent extensive abdominal surgery was identified as significant risk factors for acquiring invasive candida infection in ICU patients with a length of stay of at least seven days.

In conclusion, the results of the present study emphasize the importance of compliance to barrier treatment, implementation and continuously follow-up of infection control programmes. Furthermore, the results underline the importance of a prudent use of antimicrobial agents for therapy and prophylaxis, based on daily reconsideration of the treatment according to microbiological and laboratory results and the patient’s condition, especially in this vulnerable patient population.

List of scientific papers

I. Agvald-Ohman C, Wernerman J, Nord CE, Edlund C (2003). Anaerobic bacteria commonly colonize the lower airways of intubated ICU patients. Clinical Microbiology & Infection. 9(5): 397-405
https://pubmed.ncbi.nlm.nih.gov/12848752

II. Agvald-Ohman C, Lund B, Edlund C (2004). Multiresistant coagulase-negative staphylococci disseminate frequently between intubated patients in a multidisciplinary intensive care unit. Critical Care. 8(1): R42-47
https://pubmed.ncbi.nlm.nih.gov/14975054

III. Agvald-Ohman C, Lund B, Hjelmqvist H, Hedin G, Struwe J, Edlund C. (2006). ICU stay promotes enrichment and dissemination of multiresistant coagulase-negative staphylococcal strains. Scandinavian Journal of Infectious Diseases. 38: 441-447
https://pubmed.ncbi.nlm.nih.gov/16798690

IV. Agvald-Ohman C, Klingspor L, Hjelmqvist H, Edlund C. (2006). Invasive candidiasis in long-term patients at a multidisciplinary intensive care unit: Candida colonization index, risk factors, treatment and outcome. [Submitted]