Maintenance of Temperature during Transportation of Samples

Collection and transport

The proper collection and handling of specimens are essential for successful isolation of viruses from clinical material. Ideally, specimens for virus detection should be collected in sterile, screw tight containers and as early as possible in the course of the disease. All samples collected should be labeled with a patient name in addition to the medical record. The appropriate specimens should be delivered directly to Department of Pathology which is the sample receiving center. Virology specimens are picked up approximately four times a day in the pathology lab. Transport media that is virus transport media (VTM) is available for transportation of viral sample.

The laboratory diagnosis of viral infections is based upon following three general approaches:

1. The direct detection of viral nucleic acids, antigens or structures, either in cells derived from infected tissues or free in fluid specimens.
2. Isolation and identification of viruses usually accomplished in cell cultures.
3. Finally, demonstration of a significant increase in serum antibodies to an etiologically acceptable virus during the course of the disease.

Specimens for virus isolation and direct detection, a sample must be collected within the first few days of an illness. The collected specimens are preferable to test within three days but not longer than seven days after the onset of illness. Most viruses are better identified from specimens held at 2-6°C for up to several days. The freezing of specimens at -20°C is not preferred because the infectivity of many viruses is rapidly lost at this temperature. Urine, Fluid specimens, cerebrospinal fluid (CSF) does not require any transport medium and should not be diluted.

The different sample collected for viral diagnosis with the collection technique as well as maintenance of temperature for that collected specimen is given below:

Transport and storage

Ideally, all specimens collected for detection of the virus should be processed by the lab immediately. However, potential biohazards, difficulty in processing steps and necessary quality control make this practice impractical. Specimens for viral isolation should not be kept at room temperature. If a delay is unavoidable, a specimen should be refrigerated for placed in a bag. Every attempt should be made to process the specimen within 12-24 hrs or collection. Under unusual circumstances, the specimen may need to be held for days before processing. For storage up to 5 days, the specimen should be held at 4C storage for 6 or more days should be at -20c or preferably at -70C. 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 liable enveloped viruses.

If a commercial kit is being used, a specimen for molecular testing should be transported or stored according to manufacturers’ instruction. Many types of specimens for detection of the virus can be collected using a swab. Most types of synthetic swab material such as rayon and Dacron are acceptable. Once collected, it is recommended that specimens on the swabs be emulsified in viral transport medium before transporting to the lab, especially if transport will occur at room temperature and require more than 1 hour, calcium alginate swab is not acceptable if for the detection of HSV because it may inactivate HSV. If transferred into VTM by swirting the swab vigorously and the swab should be discarded immediately. VTM are used to transport small volume of fluid specimens, small tissues, and scrapping and, swab specimens especially when contamination with microbial flora is expected. Transport media contain proteins such as serum, albumin or gelatin to stabilize virus and antimicrobials to prevent overgrowth of bacteria and fungi. Penicillin and streptomycin have been used traditionally. However, a more potent mixture overgrowth mixture includes vancomycin, gentamicin, and amphotericin. If serum is added as protein source total serum is recommended because it is less so likely to contain inhibitors such as an antibody.

Examples of successful transport media include:

• Stuarts medium
• Amie’s medium
• Eagle’s tissue culture medium
• Hanks balanced salt solution (HBS) medium
• Leibovite - Embryo medium etc.

REFERENCE

Cheesbrough, M. Medical Laboratory Manual for Tropical Countries. Vol. Vol 2. ELBS London, 2007.

Tille, P. Diagnostic Microbiology. 13th. Elsevier, 2014.

D, Grenwood, Slack RCB and Peutherer J. Medical Microbiology. Dunclude Livingstone: ELBS, 2001.