Specimen Transport and Storage in viral infections
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p797
2025-12-17
45
Ideally all specimens collected for detection of virus should be processed immediately. Although inoculation of specimens into cell culture at the bedside has been recommended in the past, potential biohazards, sophisticated processing steps, and necessary quality controls make this impractical. Specimens for viral isolation should not be allowed to sit at room or higher temperature. Specimens should be kept cool (4°C) and immediately transported to the laboratory. If a delay in transport is unavoidable, the specimen should be refrigerated, not frozen, until processed. Every attempt should be made to process the specimen within 12 to 24 hours of collection. Under unusual circumstances, specimens may need to be held for several days before processing. For storage up to 5 days, specimens are held at 4°C. Storage for 6 days or longer should be at –20° or preferably–70°C. Specimens for freezing should first be diluted or emulsified in viral transport medium. Significant loss of viral infectivity may occur during prolonged storage, regardless of conditions, especially for the more labile enveloped viruses.
If a commercial kit is used for viral identification (e.g., nucleic acid testing), the specimens should be trans ported and stored according to the manufacturer’s instructions. Specimens for processing using commercial reagents that are not approved by the U.S. Food and Drug Administration (FDA), such as analyte-specific reagents, or assays that have been created and validated in the user’s laboratory (laboratory-developed tests [LDTs]), are transported and stored at refrigeration temperatures. Freezing at –70°C is recommended if processing is delayed for longer than 2 to 3 days.
Many types of specimens for the detection of virus can be collected with a swab. Most types of synthetic swab material, such as rayon and Dacron, are acceptable. Swabs with cotton tips and wooden shafts are not recommended. Once collected, specimens on swabs should be emulsified in viral transport medium before transport to the laboratory, especially if transport will occur at room temperature and require longer than 1 hour. Calcium alginate is not acceptable for the detection of HSV, because it may inactivate the virus. Also, as previously mentioned, it is not recommended for PCR amplification of any respiratory viruses.
Commercially prepared transport media are useful for maintaining viral stability. They are used to transport small volumes of fluid specimens, small tissues and scrapings, and swab specimens, especially when contamination with microbial flora is expected. Transport media contain protein (e.g., serum, albumin, or gelatin) to stabilize the viral agents and antimicrobials to prevent overgrowth of bacteria and fungi. Penicillin (500 units/mL) and streptomycin (500 to 1000 mcg/mL) have been used tradition ally; however, a more potent mixture is composed of vancomycin (20 mcg/mL), gentamicin (50 mcg/mL), and amphotericin (10 mcg/mL). If serum is added as the protein source, fetal calf serum is recommended, because it is less likely to contain inhibitors, such as antibodies. Examples of successful transport media include Stuart’s medium, Amie’s medium, Leibovitz-Emory medium, Hanks balanced salt solution (HBSS), Eagle’s tissue culture medium, and the commercially available M4, M5, and universal transport media. Respiratory and rectal and stool specimens can be maintained in modified Stuart’s medium, modified HBSS, or Leibovitz-Emory medium containing antimicrobials.
Blood for viral culture, transported in a sterile tube containing anticoagulant, must be kept at refrigeration temperature (4°C) until processed. Blood for viral serology testing should be transported to the laboratory in the sterile tube in which it was collected. Serum should be separated from the clot as soon as possible. Serum can be stored for hours or days at 4°C or for weeks or months at –20°C or below before testing. Testing for virus-specific IgM should be completed before freezing whenever possible, because IgM may form insoluble aggregates upon thawing, producing a false-negative result.
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