There is a wide range in the importance of bacteria as a trigger of exacerbations of respiratory disease, from a limited role in asthma and IPF to a dominant role in CF and bronchiectasis, with an intermediate role in COPD. Conventional techniques to understand bacterial infection, such as culture and antibody response studies, are being replaced with new methods, such as microbiome and immuno-inflammatory profiling, with consequent new insights and a rethinking of traditional concepts. The trend is towards recognition of a more substantial role for bacteria in exacerbations and even in stable disease pathogenesis than previously thought, with an appreciation that infections are often polymicrobial and that changes in microbial community composition can cause disruption of the stable homeostatic state leading to exacerbations. Future studies are likely to contribute further changes to our understanding in this area, with innovative therapeutic implications.

Cite as: Provost KA, Frederick CA, Sethi S. Bacterial infection. In: Burgel P-R, Contoli M, López-Campos JL, eds. Acute Exacerbations of Pulmonary Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2017; pp. 97–113 [https://doi.org/10.1183/2312508X.10016216].