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Laboratory Services Section
Viral Isolation Team- Influenza Surveillance
| Viral Testing | Electron Micrographs - Jump to: The Viral Isolation Team at the Texas Department of State Health Services identifies viruses in both patient and reference specimens submitted by physicians, hospitals, or other laboratories. Specimens may be submitted for diagnostic, reference, or surveillance testing. The laboratory receives approximately 2500 specimens annually from across the state of Texas for virus isolation studies. In addition, the laboratory serves as a referee laboratory for the New York State Virus Isolation Proficiency Program. |
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Most
specimens for virus isolation are tested by cell culture methods, including both standard
tube culture and shell vial, where appropriate. In addition, specimens may be evaluated by
electron microscopy for direct detection of viruses in the specimen. Molecular detection
methods are also used for certain viruses. Identification methods include serum
neutralization, fluorescent antibody testing, PCR, hemagglutination inhibition, and immune
electron microscopy.
Frequently Asked Questions
How do I know what source of specimen to submit? Refer to the Specimen Selection Based on Clinical Symptoms table. In addition, the specimen of choice is influenced by seasonal or regional epidemiological trends and the patient’s exposure history. When should specimens be collected? For optimal viral recovery, specimens should be collected as close to the time of onset as possible. The length of viral shedding depends on the virus, the clinical presentation, and the site sampled as well as the immunocompetency of the patient but generally declines with time after onset. How long does it take to obtain results? Turnaround time for viral isolation results varies with the test(s) performed and the rate of growth of the virus isolated. If no virus is isolated, a result is generally available in 2 weeks. However, the result may take more than 2 weeks if the specimen causes a reaction in cell cultures that appears to be due to a virus which requires follow up testing, but the follow up testing does not confirm the presence of a virus. In addition, the testing may take more than 2 weeks if the specimen has components that are toxic in cell cultures requiring additional procedures to decrease the toxic effects. If a virus is isolated, a result can be available within several days but may take weeks due to the varying times needed for some identification test results and the ease with which the virus grows. Turnaround time for influenza surveillance results is similar to that of viral isolation results. Turnaround time for dengue isolation results is generally 7-10 days. Turnaround time for electron microscopy is generally same day; however, if EM is coupled with an isolation effort, the results are normally reported at the same time. Only positive EM results are reported as the microscopy is completed. Turnaround time for C. trachomatis isolation is 7 days. What is the significance of a "No virus isolated" result? A "No virus isolated" result does not rule out the presence of a virus. Successful isolation of a virus depends on proper specimen collection including timing and site selection, proper transport or storage of the specimen, use of susceptible host systems in the laboratory, and lack of interference from contaminants or toxic components in the specimen. What is the significance of a "Viral agent isolated:......." result? The significance of a viral isolate must be interpreted based on clinical findings, the site of isolation as it relates to the organs involved, and an understanding of the pathogenesis of the virus recovered. Viruses are not considered normal flora. If a virus is isolated, that virus has caused an infection; however, it does not necessarily mean that virus is responsible for the patient’s symptoms. A virus can be isolated when a latent virus is reactivated, when virus is shed for long periods of time, or following immunization with a live virus vaccine. In these situations, a positive isolation result must be interpreted with caution. If I receive a qualification statement on a report, what does it mean? It means that the test requested was performed but was not optimal for a reason which is a part of the qualification statement. For example if our laboratory received a specimen at ambient temperatures, a qualifying statement will be included which reads, "Results may be invalid because specimen was received warm." LinksNote: External links to other sites are intended to be informational and do not have the endorsement of the Texas Department of State Health Services. These sites may also not be accessible to people with disabilities.
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Last Updated December 1, 2004
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