Quality Control in Clinical Virology


Quality Control Slide Set

Quality control in the clinical laboratory consists of a set of procedures designed to help ensure delivery to the medical staff of laboratory results that are consistent and accurate. These results must be supplied in a timely fashion while the data is still clinically relevant. A clinical virology laboratory should be designed in a manner so that biohazard risks to the laboratory personnel and the general public is minimized and that cultures are protected from environmental contamination. A facility designed specifically for clinical virology should;-

  1. Be physically separate from the microbiology laboratory and not share common air returns or equipment such as hoods and incubators.
  2. The environment should be controlled so that the ambient temperature is 22 - 26oC and the relative humidity 30 -50%.
  3. The facility should be under negative pressure with respect to the rest of the laboratory area.
  4. Internally, the laboratory can be divided into positive and negative air pressure areas; the positive for tissue culture and media preparation, the negative for viral isolation or serology because they deal with viable pathogens.
  5. All surfaces should be composed of materials that can be decontaminated easily.
  6. Good standard microbiology measures should be observed such as daily decontamination of all work surfaces, proper laboratory attire, use of safe pipetting devices, and to minimize aerosol generation.
  7. Biological safety hoods should be available for tissue culture and viral isolation. Hood rooms should not have common air ducting and the exhaust from hoods in which pathogens are handled be externally vented.
  8. The facility must be properly maintained; biohazard wastes properly disposed, floors disinfected periodically, air pressure balance checked.  


Written Procedures

Two sets of written procedures are important. One is for use by medical staff and the other for laboratory use as procedure manuals. The procedures for medical staff should include;-

  1. Purpose and limitations of the test
  2. Hours the test is performed
  3. Test turnaround times
  4. Types and quantity of specimen required
  5. Specimen transport and holding instructions  

The procedure manual used in the laboratory should be complete enough in detail so that an inexperienced technologist can perform the procedure without additional information. One copy of the manual should be readily available to bench personnel, another copy should be stored separately in case of accidents.

Specimen Transport

Specimens for viral isolation are often held for long periods of time before it reaches the laboratory. Enveloped viruses such as RSV and CMV are extremely liable to room temperature and freeze-thaw cycles whereas non-enveloped viruses such as enteroviruses tolerate these conditions well. As a general rule, viral specimens held for short periods should be refrigerated, while those for longer periods may be frozen at -20 or -70oC.

Transport Media - the composition and type of viral transport media can affect viral isolation rates. In general, the media should be a balanced isotonic solution at physiological pH. It should contain a substance that will stabilize the virus such as gelatin, fetal calf serum or bovine serum albumin, and antibiotics against bacteria and fungi. The swab should be made of a material that is non-toxic to viruses, such as dacron or rayon.

Smears - smears are becoming increasingly popular because of the rapidity of staining techniques. The smear should contain a reasonable number of cells, be of a reasonable size and not over-contaminated by blood or pus, as the latter may lead to nonspecific staining.

Specimens for Serology - Excessively haemolysed, lipaemic, bacterially contaminated, or leaking specimens should be rejected. Sera should be heat-inactivated depending on the tests to be performed. In the event of a specimen being rejected, the ward must be informed, preferably by an oral report followed by a written one. Extenuating circumstances may warrant the acceptance of a substandard specimen.   

Tissue Culture and Media

Tissue culture remain the mainstay of non-serologically viral diagnosis. Therefore, adequate quality control for commercially purchased or for in-house preparation of tissue culture cells is of great importance. Within a given cell line, there may be significant variations in sensitivity to virus isolation which may depend on the particular cell subline or clone and the passage number. Information on a particular cell line should be recorded pertinently including the source, type, passage number, confluency and cell condition. The loss of a cell line routinely passaged for use can lead to a severe disruption of workflow and therefore, provisions must be made for back-up cells in the event of contamination or laboratory accident. These back-up systems include;

  1. Freezing and storage of low passage cells at -70oC
  2. Use of paired stock flasks. When the flasks reach confluency, only one is passaged, while the second flask is held as a back up until the new flask displays good growth.
  3. Carrying of a parallel set of stock flasks using a separate set of tissue culture reagents and glassware.

Cells purchased from a commercial company should be certified to be free from mycoplasma, fungal, and bacterial contamination and examined for contamination on receipt. Tissue culture lines carried in-house should be subjected to;

  1. Daily checks for growth rate and contamination
  2. Mycoplasma contamination monitored monthly by Hoechst stain.
  3. The sensitivity to viral isolation monitored by periodic TCID50 experiments with stocks of reference virus.

Other quality control procedures that may aid in minimizing the risk of contamination include the exclusion of laboratory with infectious diseases from handling tissue culture, separate laboratory apparel, reagents and glassware for tissue culture. Cell lines should be handled separately and the cabinet be decontaminated in between.

Media - following filter sterilization, aliquots of the media should be taken and checked for bacteriological or fungal investigation. These samples should be examined daily for 5 days and should be free from contamination before that lot of medium is released for use. Aliquots of all other medium components such as fetal calf serum and L-glutamine should also be checked. New lots of medium and fetal calf serum that have passed the sterility check should be monitored for their ability to support cell growth.

Reagents and Kits

Reagents and kits should be ordered from reputable manufacturers or dealers with reliable transportation systems. Upon receipt, the reagents should be checked for obvious breakage or contamination. The quantity, source, lot number and date of receipt should be entered in a logbook and the reagents stored according to the manufacturer’s storage specifications. When new lots of any reagent are opened, the date should be noted on the container. Caution must be exercised in the case of kits as different components of a kit may have different storage conditions and expiration dates.  


Laboratory instruments should be subjected to routine preventive maintenance and checked and calibrated on a regular basis. Some of these checks can be performed by laboratory staff and entered into a logbook. The following are some recommendations for routine laboratory maintenance and performance checks on instruments.

  1. Incubators - daily temperature, CO2 and humidity checks. Weekly decontamination of interior
  2. Safety cabinets - daily air pressure check and cleaning of UV lamp. Work surface should be decontaminated after each use. Annual checks for air velocity and filter integrity and paraldehyde decontamination as applicable.
  3. Microscopes - daily cleaning of objectives and stage, log of lamp usage and annual overhaul
  4. Refrigerators and freezers - daily temperature check; annual check of compressor and refrigerant levels
  5. Water baths - daily temperature checks, weekly decontamination
  6. Centrifuges - weekly decontamination, quarterly speed calibrations with tachometer, annual inspection of motor and drive system
  7. Autoclaves - daily temperature check and spore strip testing
  8. pH meters - single reference buffer check before each use, multiple point check monthly
  9. Pipetting devices - gravimetric volume check monthly; annual overhaul

Laboratory Accreditation