Clinical Approach to the Treatment of Infectious Diseases

Abstract

A clinician approaching a patient with an infectious disease needs to consider both the host and the pathogen. Different hosts may be more or less likely to be infected with a particular pathogen. Therefore, the clinician needs to pay considerable attention to the status of the host. Is the patient someone who has just received chemotherapy and therefore has no circulating neutrophils? If so, this patient will be predisposed to aerobic gram-negative and gram-positive bacterial infections and should be treated even if minimal signs of infection are present. On the other hand, if this patient is a normal host, one would expect the infected individual to manifest signs and symptoms characteristic of a localized infection. For example, most people presenting with bacterial pneumonia will have the classic triad of fever, productive cough, and signs of consolidation on physical examination and chest X-ray. Most of these people will have pneumonia caused by S. pneumoniae, making the therapeutic decisions about what antibiotic to use very easy. In the case of a patient without circulating neutrophils, productive cough or sputum will be absent because in order to generate sputum or have a productive cough, one needs neutrophils. Similarly, neutrophils that migrate to the site of the bacterial infection initiate the release of inflammatory cytokines that cause the local accumulation of fluid that leads to changes on chest X-rays and related findings on physical examination. The clinician will hear the consequences of fluid in the lung as “signs of consolidation,” usually detected as egophony, on physical exam.