Diagnosis of bacterial infection

Accurate diagnosis of bacterial infection is crucial to avoid unnecessary antibiotic use and to focus appropriate therapy. Bacterial infection is the combination of the presence of bacteria and inflammation or systemic dysfunction; therefore, more than one diagnostic modality is usually required for confirmation. History and examination to determine if a patient fits a clinical case definition is sometimes adequate to confirm or exclude a diagnosis. The second stage is bedside tests – some are used widely, such as urine dipstick tests, but others, such as skin scrapings of petechial rashes, are underutilised. The third stage is laboratory tests – indirect non-culture-based tests, including C-reactive protein and procalcitonin tests, when negative, can be used to prevent the unnecessary use of antibiotics. Direct non-culture-based tests detect antigens or specific antibodies, e.g. group A streptococcal antigen testing can be employed to reduce antibiotic use. Culture-based tests are often considered the reference standard in modern microbiology. Because of slow turnaround times, these tests are frequently used to focus or stop antibiotic therapy after empiric initiation. Nucleic acid amplification tests raise the possibility of detecting organisms with high sensitivity, specificity and reduced turnaround time, and novel diagnostic modalities relying on nanotechnology and mass spectrometry may dramatically alter the practice of microbiology in future.