Viral Testing

Specimen Selection

Select the appropriate specimens for viral isolation based on the clinical symptoms as outlined in the Viral Specimen Selection Table.

Specimen Collection

Collect specimens as outlined in the Viral Specimen Collection Table, as soon after onset as possible. The best specimens for viral isolation are those collected during the first 3 days after onset of symptoms.

Collect all specimens as aseptically as possible. Swabs used to obtain specimens for viral isolation should be made of Dacron with plastic. Avoid swabs with wooden shafts. DO NOT USE CALCIUM ALGINATE SWABS FOR VIRAL ISOLATION SPECIMENS.

All swabs and small tissue specimens for viral isolation should be placed in viral transport media (VTM). Typically, viral transport media consists of protein such as bovine serum albumin or gelatin to stabilize the virus and antimicrobial agent in a buffered salt solution. Transport medium can be purchased commercially. Swabs should be placed in 2-3 ml of medium, larger volumes of medium should not be used because of the dilution effect.

Place each specimen into a separate, leakproof container labeled with the patient’s name, the collection site, and the date of collection. For additional information on the packaging of specimens, view the TDSHS Manual of Reference Services.

Specimen Submission Form

Complete a G-2V specimen submission form for each specimen submitted to the Viral Isolation Section. Specimens will not be tested without a completed G-2V form. Follow the Guidelines for Specimen Shipping and Mailing for shipping specimens to the laboratory.  Forms may be obtained from the Laboratory Office.

Specimen Transport and Handling

Specimens for viral isolation should be transported to the laboratory as quickly as possible after collection since the chance of isolating a virus declines with increased time in transit. Samples containing labile viruses (i.e. respiratory syncytial virus, cytomegalovirus and varicella zoster virus) at low titers are those most likely to show loss of infectivity with delayed transport. For short-term transit or storage, specimens should be kept at refrigerator temperatures on wet ice or cold packs. If a longer transit time is anticipated, the specimen should be frozen at -70° C and transported to the laboratory on dry ice. Specimens submitted for Varicella Zoster isolation must be received at the DSHS Laboratory cold, on ice packs, within 12 hours of collection, or freeze and ship on dry ice. Refer to Specimen Submission and Selection for specific acceptance criteria.

Specimens for direct detection (i.e. EM) should be kept at refrigerator temperatures on wet ice or cold packs. Freezing specimens for direct detection is not optimal.

Specimens must be transported in accordance with all safety and labeling regulations. The TDSHS Manual of Reference Services includes detailed instructions for packaging and shipping specimens and isolates.

Testing Methods

Viral Isolation

Viruses cause a wide range of clinical symptoms and are shed from various anatomical sites during the infection. The site selected for specimen collection should be based on the clinical symptoms (view the Viral Specimen Collection Table) and the seasonal and/or local epidemiological trends. Once a specimen is received in the laboratory, it is processed and inoculated into living host systems (i.e. cell cultures). Inoculated host systems are incubated to allow any virus present in the specimen to grow and replicate. During the incubation period, if observation indicates the presence of a virus, additional laboratory tests are performed to confirm the virus’s presence and identity.

Reference Culture: Viral Isolation

Laboratories that would like final identification and/or confirmation of their results may send isolates to the DSHS Laboratory.

Isolates can be sent either frozen on dry ice or at ambient temperatures in cell culture monolayers that are shipped when CPE is first evident in the monolayers. Fill the tube or vial with media to prevent drying of the monolayer during transit if the tube or vial gets turned during transit.

Electron Microscopy

The electron microscope has been an invaluable tool for the basic understanding of viruses. Clinical application of the electron microscope has yielded another use: the rapid and unequivocal recognition of viruses. The results of studies with the electron microscope during the past have ranged from describing a new virus for the first time to the rapid recognition of viruses in clinical specimens.

The use of the electron microscope in the detection and identification of viruses offers many advantages. Using a negative stain technique, results are generally available in hours, not days. The infectivity of the virus does not need to be maintained, and viruses which are difficult or impossible to culture can be identified. The approach is open-ended which allows a wide variety of agents to be visualized, and since the actual agent is visualized, there are no false positive results.

Specimens for electron microscopy should not be placed into transport medium or fixative. Package specimens on wet ice or cold packs and transport as quickly as possible. Do not freeze specimens for electron microscopy.

View sample electron micrographs

Real-Time Reverse-Transcription PCR

Real-Time Reverse-Transcription (rRT-PCR) testing is available for the identification and subtyping of influenza virus and for the identification of measles and mumps virus. In addition, rRT-PCR is available for the identification of Middle East Respiratory Syndrome Coronavirus (MERS-CoV). Prior approval is required for MERS-CoV testing. Contact Crystal Van Cleave for more information regarding MERS-CoV testing at (512)-776-7594.