Specimen Collection, Transport, and Processing: Bacteriology

One of the key principles of good specimen collection is to avoid introduction of colonizing bacteria surrounding the site of infection or on the skin or mucous membranes near the infectious site. A relatively recently introduced type of swab, the flocked swab, has proved to be superior to fiber swabs for collection of nasopharyngeal samples for detection of respiratory viruses, but there were no significant differences between flocked and rayon swabs when throat cultures were evaluated. For abscess contents, body fluids, and other fluid collections below the skin, aspirates obtained through disinfected intact skin are preferred over swabs. Expectorated sputum is the best sample for diagnosis of pneumonia, a disease of the distal lung alveolar spaces. Urine can be collected by midstream collection, catheterization, cystoscopic collection, or suprapubic aspiration. Urine specimens should be transported to the laboratory immediately and processed within 2 h of collection. Testing more than one stool for bacterial pathogens is usually not productive. Fresh stool should be examined visually, and the areas showing blood, pus, or mucus should be sampled preferentially. In spite of acceptable labeling, some specimen collection sites, transport containers, or transport conditions render the specimen unacceptable for processing. Although blood has not yet been used widely for detection of bacteria using nucleic acid amplification (NAA) tests or hybridization, such tests are in development. Swabs should be transported to the laboratory in special media.