Laboratory Diagnosis

A key decision made early in the microbiological diagnostic workup is whether the patient's clinical signs indicate a possible infectious etiology. Attention must be paid to how the diagnostic specimens are collected; if not, interpretation of the results may be difficult. The sooner the specimen is processed in the microbiology laboratory, the greater the probability of obtaining useful outcomes. The presence of an infectious agent may be accomplished by examination of stained smears made from a portion of the clinical sample, culture techniques, molecular/immunologic methods, or a combination of these methods. Viruses are isolated from clinical specimens by inoculating susceptible primary or continuous cell cultures derived from the host or related species, embryonated eggs, or laboratory animals. The specific etiologic diagnosis of viral diseases traditionally has been both tedious and time-consuming, but modern technologies such as PCR have increased the utility of this approach.