Infectious Diseases of the Respiratory Tract

Introduction

Although anaerobic lung infection has been recognised for a century the precise contribution of anaerobic bacteria to community- and hospital-acquired pneumonia, lung abscess and empyema has been clarified only in the last 20 years. The development of specialised sampling techniques to reduce contamination, together with dedicated anaerobic culture techniques have shown that the role of anaerobic bacteria as pulmonary pathogens had previously been greatly underestimated. Changes in taxonomy have impacted on the reporting of the relative contributions of different bacteria. The observation that it is more usual to find polyanaerobic and mixed anaerobic/aerobic organisms from appropriate specimens and that some organisms are resistant to antimicrobials has had major implications for treatment.

This chapter summarises the current status of anaerobes in lung infection, including the presentation and management of the post pneumonic sequelae of abscess and empyema.

Anaerobic pulmonary infection

Pathogenesis

Aspiration of oropharyngeal secretions which contain saturated levels of anaerobes of up to 1012 organism per gram, which if excessively frequent and voluminous overwhelm the lungs clearance capacity (which normally removes the smaller quantities encountered in healthy people), is the major initiating mechanism in the genesis of anaerobic lung infection. Predisposing conditions have been described previously (Table 20.1 and Chapter 28) which include breaching of mechanical defence barriers, for example, by endotracheal tubes, depressed level of consciousness, for example, cerebrovascular accidents and intestinal dysmobility, for example oesophageal disease.