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Classification of Microorganisms According to Their Pathogenicity

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Infection Control in the Intensive Care Unit

Abstract

Microorganisms are classified into three major groups: low-level pathogens, high-level pathogens, and potential pathogens. They are classified using the intrinsic pathogenicity index (IPI), defined as the ratio between the number of patients infected by a particular microorganism and the number of patients who carry the identical microorganism in the throat and/or gut. Indigenous anaerobes rarely cause infections, despite being carried in high concentrations by everyone, and have an IPI between 0.01 and 0.03. Enterococci and coagulase-negative staphylococci are also carried in the oropharynx in high concentrations by a substantial percentage of patients requiring treatment in the intensive care unit but are unable to cause lower airway infections. These are low-level pathogens, whereas high-level pathogens such as Salmonellae have an IPI approaching 1. There are about 15 potential pathogens with IPIs between 0.1 and 0.3. These include six normal potential pathogens carried by healthy individuals and nine abnormal potential pathogens carried by patients with an acute or chronic condition. Evidence supports the concept that antibiotic resistance does not contribute to mortality.

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Author information

Authors and Affiliations

  1. Department of Intensive Care Medicine, Hospital Universitario de Getafe, Getafe, Spain

    M. A. de la Cal

  2. Department of Intensive Care Medicine, Hospital Universitario de Parla, Madrid, Spain

    E. Cerdà

  3. Department of Intensive Care Medicine, Hospital Universitario de Getafe, Madrid, Spain

    A. Abella

  4. Department of Medical Microbiology, Hospital Universitario de Getafe, Madrid, Spain

    P. Garcia-Hierro

Authors
  1. M. A. de la Cal
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  2. E. Cerdà
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  3. A. Abella
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  4. P. Garcia-Hierro
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Corresponding author

Correspondence to M. A. de la Cal .

Editor information

Editors and Affiliations

  1. , Institute of Aging and Chronic Diseases, University Liverpool, Daulby Street, Liverpool, L69 3GA, United Kingdom

    Hendrick K.F. van Saene

  2. , Dept. Emergency, Hospital Gorizia, Via Vittorio Veneto 171, Gorizia, 34170, Italy

    Luciano Silvestri

  3. , Department of Intensive Care Medicine, Hospital Universitario de Getafe, Carretera de Toledo km 12.5, Getafe, 28045, Spain

    Miguel A. de la Cal

  4. Policlinico di Catania, UCO di Anestesia e Rianimazione, Azienda Ospedaliero-Universitaria, Via Santa Sofia 78, Catania, 95100, Italy

    Antonino Gullo

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de la Cal, M.A., Cerdà, E., Abella, A., Garcia-Hierro, P. (2011). Classification of Microorganisms According to Their Pathogenicity. In: van Saene, H., Silvestri, L., de la Cal, M., Gullo, A. (eds) Infection Control in the Intensive Care Unit. Springer, Milano. https://doi.org/10.1007/978-88-470-1601-9_3

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  • DOI: https://doi.org/10.1007/978-88-470-1601-9_3

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  • Publisher Name: Springer, Milano

  • Print ISBN: 978-88-470-1600-2

  • Online ISBN: 978-88-470-1601-9

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