Lab Testing for Rubella
If you suspect rubella, specimens should be collected for both culture and serology.
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Rubella and measles should both be included in the differential diagnosis of patients presenting with an acute generalized rash and fever.
Collect specimens for both culture and serology. The only reliable evidence of acute rubella infection is the presence of one or more of the following:
- A positive rubella-specific IgM antibody,
- A significant rise in IgG antibody from paired acute and convalescent sera,
- A positive viral culture for rubella, or
- Detection of the virus by reverse transcription-polymerase chain reaction (RT-PCR).
Rubella is characterized by:
- Acute onset of a maculopapular rash lasting < 3 days
- Fever >99°F (>37.2°C)
- Arthralgia, arthritis, lymphadenopathy, or conjunctivitis
Measles is characterized by:
- A generalized maculopapular rash lasting >3 days
- Fever >101°F (38.3°C)
- Cough, coryza, or conjunctivitis
Draw blood in a red-top tube and spin down serum if possible, only 1-2 ml is needed.
- Draw blood for IgM antibody testing at least 96 hours after rash onset.
- If blood is drawn earlier and the rubella IgM antibody result is negative, draw another blood specimen and run for repeat testing.
Other diseases, such as parvovirus infection, infectious mononucleosis, or rheumatologic disease can cause false positive rubella IgM antibody results.
- Obtain acute and convalescent serum specimens for rubella specific IgG antibody to confirm a rubella diagnosis. This is especially important if the rubella specific IgM antibody titer is drawn at the wrong time or confounded by other infections.
- Draw blood for acute IgG as early as possible when rubella infection is suspected. For convenience, however, you can use the blood drawn for rubella IgM antibody for acute IgG testing.
- Draw blood for a convalescent IgG 3 to 5 weeks after blood was drawn for the acute IgG.
Possible interpretations of a single positive measles IgG antibody result include:
- Current infection to which the individual is developing immunity.
- Immunity due to either a past infection or vaccination.
- Presence of maternal antibody (in infants < 15 months).
The earlier that blood is drawn for rubella IgG antibody following the onset of symptoms, the more likely a positive result is due to past infection or vaccination.
Rubella virus can best be isolated from (in order of preference): nasal, throat, urine, cerebrospinal fluid, and blood specimens.
Ideally, all three of the following specimens should be collected: a nasal wash (if that is not possible, a nasal swab), a throat swab, and urine for culture.
1. Nasal wash (two techniques)
Use a syringe attached to a small plastic tube and 2 ml of viral transport media (VTM). After placing VTM in the nostril, aspirate as much of the material as possible and rinse the tube with the original (2 ml) of VTM.
- Or -
Use sterile swabs to swab the nasopharynx and throat with either a viral culture swab or culturette. Do not use special (e.g., anaerobic) media. Place both swabs in a tube containing 2-3 ml of transport medium. The virus is extremely cell-associated, so attempt to swab the throat and nasal passages to collect epithelial cells. After swabbing, place the swab back in the transport sheath.
2. Throat swab
Vigorously swab tonsillar areas and posterior nasopharynx with a viral culturette. Use tongue blade to depress tongue to prevent contamination of swab with saliva. Place swab into Viral Transport Media (VTM).
3. Urine specimen
Collect 10-40 ml of urine in a STERILE 50 ml centrifuge tube or a urine specimen container. First-morning voided specimens are ideal, but any urine collection is adequate. Have patient void directly into container, collecting from the first part of the urine stream if possible.
Specimen colllection: PCR
Rubella PCR is a highly sensitive and timely laboratory test. This test may be available through your usual commercial laboratory. Contact an MDH epidemiologist at 651-201-5414 or toll-free at 877-676-5414 to facilitate testing for situations in which rapid case confirmation is critical.
- Collect and send in red-top tube.
- Send in viral transport medium OR
- Use a viral culturette swab.
- Collect and send in sterile container.
Serum and culture specimens should be refrigerated. Label the tubes/containers with patient name, date of birth, and date collected. For shipping to MDH, specimens should be kept cool (e.g., in a Styrofoam container with freezer packs), and submitted as soon as possible (preferably same day delivery).
Include an MDH lab request slip for each specimen submitted. If original lab-slip forms (printed in triplicate) are not available, submit another form including the same information (patient name, address, birth date, sex, collection date, type of test requested, and type of specimen submitted) or obtain the Request for MDH Virology Specimen Submission Form
Send to MDH Public Health Laboratory via overnight shipping. When the specimen is sent, notify an epidemiologist at MDH at 651-201-5414 or toll free at 877-676-5414.
Send specimens to:
Minnesota Department of Health
Specimen receiving – biological accessioning
601 Robert St. N.
PO Box 64899
St. Paul, MN 55164-0899