Virological tests are usually costly and labour-intensive, therefore they should be undertaken only when good clinical indications for doing so exist, and after thoughtful consideration of the types of tests to request for.
Virological tests fall into three categories:
All samples must be clearly labelled with the patient’s name and unique identification number, e.g. NRIC number, as well as the nature, source and date of collection of the sample.
Each sample must be accompanied by a request form that is completed legibly with the patient’s name, unique identification number, location, relevant history, findings and clinical diagnosis, the test(s) required, the nature, source and date of collection of the sample, and the name and for urgent requests, the contact number of the requesting doctor. The form must be signed by the requestor.
It should be ensured that these requirements are met to avoid rejection of the sample by the laboratory or a delay in reporting.
Nasopharyngeal aspirates are superior to throat swabs for the recovery of viruses. Further, immunofluorescence microscopy can be carried out on exfoliated cells in the aspirate for rapid diagnosis.
For mumps isolation, swab the buccal mucosa opposite the upper molars where Stensen’s ducts open, then swab the floor of the mouth at the openings of the submandibular gland ducts. For cytomegalovirus (CMV) isolation, swab the buccal mucosa or aspirate saliva into a mucous trap and send in VTM.
Sample fresh skin vesicles during the first three days following the appearance of the eruption. Crusted lesions have a lower chance of yielding viable virus. Macules or papules should not be sampled.
Clean open lesions on the skin and genitalia with sterile saline to remove any pus, then swab firmly to sample the basal cells. For oral lesions, swab the base of the lesions. Insert the swab into a bottle of VTM, break off the stick and screw-cap the bottle tightly.
In the case of keratoconjunctivitis, send scrapings from lesions for virus isolation and/ or immunofluorescence.
Using a swab moistened with sterile saline, pull down the lower lid and swab the conjunctiva firmly, then evert the upper lid and swab similarly. Insert the swab into a bottle of VTM, break off the stick and screw-cap the bottle tightly.
For keratoconjunctivitis, send scrapings from lesions for virus isolation and/ or immunofluorescent antigen test.
Send fresh samples for virus isolation. Formalinised or fixed tissues cannot be used, as the virus would have been destroyed. Place a piece of the sample about 1 cm in size (or smaller if necessary) directly into the bottle of VTM, and screw-cap the bottle tightly. Place the bottle in a specimen bag, seal it,
and place this bag in an outer plastic bag containing ice or an ice-pack. Send immediately to the laboratory.
For adults, instruct the patient to clean the urethral/vulval and perineal areas with soap and water, before collecting a mid-stream sample in a sterile bottle. For infants and young children, clean the perineum and genitalia and collect the sample in a sterile bottle. Transfer the urine into a urine culture bottle up to the mark indicated (about 10 mL). This bottle, which contains antibiotics, can be obtained from the Client and Specimen Management Section of the Department of Clinical Pathology.
Stool can be sent for virus culture to diagnose enteroviral infections. The virus is excreted in the faeces for several weeks.
Most of the viruses that cause gastroenteritis such as rotavirus, the enteric adenoviruses and the caliciviruses, cannot be cultured in tissue cultures at present, and virus isolation is usually non-productive for viral gastroenteritis.
With CMV enteritis, stool cultures are usually negative and an intestinal biopsy sample is required for virus isolation or antigen detection.
Stool in amount equivalent to the tip of the little finger should be collected in a sterile bottle without VTM.
Collect from cases with suspected enteroviral infections only when stool is difficult to collect, as rectal swabs are inferior to stool.
Insert a sterile swab at least 3 cm deep into the anal orifice of an adult and rotate it to ensure collection of faeces. Place the swab in a bottle of VTM, break off the swab stick and screw cap the bottle firmly.
Viruses may be isolated from leucocytes and/or plasma so send unclotted blood.
Collect 1 – 2 mL CSF in a sterile bottle without VTM.
Collect 3 – 4 mL of fluid in a sterile bottle without VTM.
* EIA: Enzyme Immunoassay
† CFT: Complement Fixation Test
Enteroviruses: throat swab in VTM and stool. Dengue and chikungunya: Blood
Measles: NPA, TS, sputum, brain, lung, skin in VTM, urine, EDTA blood. Rubella: TS, nasal swab, NPA, placental tissue, lung, brain in VTM, urine, EDTA blood, uncoagulated cord blood, amniotic fluid, CSF