Antimicrobial agents are the cornerstones of bacterial pneumonia therapy. In fact, there are convincing data to show that patients with pneumonia have a better chance of survival if given antibiotics. Initial antibiotic choice should be based on expected etiological pathogens, while knowledge of local microbial epidemiology and susceptibility patterns is crucial. Characteristics of the antibiotic itself, such as microbiological activity (bactericidal or bacteriostatic mode of action) and the spectrum of activity of the compound are relevant to choice of treatment. The frequency of side-effects and the interference with immunological homeostasis, as well as the ability to pass from capillary bed to bronchial lumen across a series of membranes and diffusional paths (the so-called blood-bronchoalveolar barrier), also influence the choice of the antibiotic to be used.

Microbiological Problems

Because antibiotic therapy is usually initiated before the results of bacteriological analysis are available, the physician must take into account the potential pathogens and their current susceptibilities to available antimicrobial agents.

Incidence

Epidemiological data, including geographic setting, seasonal timing and a history of occupational or unusual exposures, may be crucial in determining the aetiology of pneumonia. However, it is important to differentiate between infections that are community acquired and those that are hospital-acquired (Table 14.1). The relative frequencies with which individual agents cause pneumonia are quite different in these two locations.

Community-acquired pneumonia (CAP) is a common illness associated with significant morbidity and mortality.