Specimens for Detection of Measles RNA by RT–PCR or Virus Isolation
Detection of measles RNA in a clinical sample can provide laboratory confirmation of infection. Real–time RT–PCR (rRT–PCR) and conventional, endpoint RT–PCR to detect measles RNA are performed at CDC. These protocols are available upon request (email firstname.lastname@example.org). The rRT–PCR is more sensitive than endpoint RT–PCR assay for detection of measles RNA in clinical sample, while the endpoint assay is routinely used to amplify the region of the measles genome required to determine the genotype. (See Genetic Analysis of Wild–type Measles Viruses.)
Samples to Collect
Throat (oropharyngeal), nasal or NP (nasopharyngeal) swabs are the preferred samples for virus isolation or detection of measles RNA by RT–PCR. Synthetic swabs are recommended. Urine samples may also contain virus and when feasible to do so, collection of both samples can increase the likelihood of detecting the virus. Collect samples as soon after rash as possible. The sample should be collected at the first contact with a suspected case of measles when the serum sample for diagnosis is drawn.
Detection of measles RNA and measles virus isolation are most successful when samples are collected on the first day of rash through the 3 days following onset of rash. However, virus may still be recovered by cell culture through day 10 following rash onset. Detection of measles RNA by RT–PCR may be successful as late as 10–14 days post rash onset.
Guidelines for Preserving Samples for Measles Virus Detection
Measles virus is sensitive to heat and infectivity decreases markedly when samples are not kept cold. It is important to transport samples with cold packs as soon as possible following sample collection. Avoid repeat freeze-thaw cycles or freezing at -20°C (standard freezer temp) because formation of ice crystals decreases infectivity. If -40°C or -70°C freezers are not available, it is recommended to keep the sample in the refrigerator (4°C).
Throat, NP or nasal swabs should be transferred to 1-3ml of viral transport medium (do not allow to dry out). The entire sample can be frozen at -70°C or if low temperature freezers are not available, keep the sample at 4°C and ship on cold packs.
Measles virus is present in the cells that have been sloughed off in the urinary tract. For optimal virus preservation, centrifuge 10-50ml of urine (500 x g (about 1500 RPM) for 10 minutes, preferably at 4°C. Resuspend the sediment in 2-3 ml of sterile transport medium, tissue culture medium or physiological buffered saline. If ultra-low freezers are available, freeze the resuspended urine sediment at -40°C or -70°C and ship frozen. If facilities for processing the urine are not available, keep the uncentrifuged urine sample at 4°C and ship on cold packs as soon as possible in a leak-proof container.
CDC is a designated WHO Measles Strain Bank and requests submission of viral isolates or clinical specimens from cases of measles for genetic characterization.
Clinical specimens or measles virus isolates should be accompanied by the CDC STAT submission form.
For additional information and to notify the CDC Measles Laboratory of specimen shipments, please contact:
Telephone: 404-639-1156 or 404-639-3512
STAT Unit #81 Att: Dr. Bellini
Centers for Disease Control and Prevention
1600 Clifton Road NE, MS C22
Atlanta, GA 30333
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