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Rubella - German Measles. ARUP Consult®. Retrieved November 21, 2024, https://arupconsult.com/content/rubella-virus

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Rubella - German Measles

Last Literature Review: November 2023 Last Update:

Medical Experts

Contributor

Slev

Patricia R. Slev, PhD, D(ABCC)
Patricia R. Slev, PhD, D(ABCC)
Professor of Pathology (Clinical), University of Utah
Section Chief, Immunology; Medical Director, Immunology Core Laboratory, ARUP Laboratories

Rubella (also known as German measles) is a viral illness that primarily affects young children. Although it was declared eliminated in the United States in 2004, infection is still possible due to international travel, and unvaccinated individuals are at risk of contracting the disease. In pregnant individuals, particularly during the first trimester, rubella infection can result in fetal death or congenital rubella syndrome (CRS), which is characterized by a range of severe birth defects.   

Clinical diagnosis of rubella is considered unreliable because infection is often asymptomatic, and, when present, symptoms are nonspecific (eg, rash and fever). Laboratory testing is required to diagnose rubella and determine past infection or immunization status. Nucleic acid amplification testing (NAAT) and serologic testing are used depending on the clinical scenario.   

Quick Answers for Clinicians

Who should be tested for rubella?

Although rubella has been declared eliminated in the U.S., domestic exposure and infection are still possible as a result of international travel. According to the CDC, testing for rubella is indicated when exposure is suspected in the following populations:

  • Pregnant individuals, regardless of whether they present with symptoms 
  • Newborns and infants (ie, exposed in utero) 
  • Unvaccinated, symptomatic adults and children, especially after international travel 

Laboratory testing is especially important in pregnant individuals and newborns due to the potential health consequences of infection in utero. Pregnant individuals should be tested for both immunoglobulin M (IgM) and IgG antibodies. 

Symptoms of rubella are typically nonspecific and include maculopapular rash (often starting on the face before spreading across the body), fever, lymphadenopathy, arthralgia, arthritis, and conjunctivitis.  Findings suggestive of congenital rubella syndrome (CRS) in newborns and infants include cataracts, congenital glaucoma, congenital heart disease, hearing impairment, and pigmentary retinopathy. 

How is protection against rubella determined?

According to the CDC, individuals who meet any of the following criteria are presumed to have immunity to rubella :

  • Written documentation of at least one dose of a vaccine containing live rubella virus at or after 1 year of age
  • Laboratory evidence of rubella immunity (resulting from immunization or past infection)
  • Laboratory confirmation of rubella disease
  • Born before 1957

When necessary, an individual’s immunity can be assessed by serologic testing for immunoglobulin G (IgG) antibodies against rubella.  For more details, refer to the Confirmation of Immune Status section.

Should all pregnant individuals be screened for rubella?

Currently, universal screening for rubella in pregnant individuals is not recommended. In regions where rubella has been eliminated, false-positive serologic results are more likely to occur due to cross-reactivity with more common pathogens. Consequently, if serology is used to screen a pregnant person with little or no risk of infection, additional testing should be performed to confirm a positive result.  Refer to the Laboratory Testing section for more information.

Indications for Testing

Pregnant Individuals

Pregnant individuals exposed to rubella should be tested, regardless of whether they present with symptoms.  Routine screening of individuals without symptoms or suspected exposure is not recommended.  

Infants

Laboratory testing may be appropriate in infants presenting with one or more findings suggestive of congenital rubella syndrome, including cataracts, congenital glaucoma, congenital heart disease, hearing impairment, or pigmentary retinopathy.  Testing should also be performed in infants exposed to rubella in utero.  Additional information can be found in the CDC’s case definition for CRS. 

Adults and Children

Laboratory testing for rubella may be appropriate in unvaccinated, symptomatic adults and children, especially after recent international travel or exposure to a person with symptoms suggestive of rubella.  Additional information can be found in the CDC’s case definition for rubella. 

Laboratory Testing

Rubella

In cases of suspected rubella, infection can be identified with serology and NAAT.

Immunoglobulin M (IgM) serology, preferably by enzyme immunoassay (EIA), can be used within the first several days of rash onset to detect a current or recent rubella infection. IgM results should be interpreted cautiously in early infection, as only 50% of cases are positive on the first day of rash onset.  If serum is collected fewer than 5 days after rash onset and results are negative, repeat testing of a second sample should be considered to confirm or rule out rubella infection.  Notably, false-positive IgM results are possible for up to 45 days after immunization against rubella. 

IgG serology to assess avidity or seroconversion may be useful in diagnosis as well. IgG avidity testing can help distinguish between a recent and past infection, whereas paired IgG serology (ie, on samples collected 7-21 days apart) can be used to detect acute infection. IgG antibodies are often detectable 8 days after rash onset. 

Pregnant individuals exposed to rubella should be tested for both IgM and IgG antibodies, regardless of whether they present with symptoms. 

NAAT, such as by reverse transcription polymerase chain reaction (RT-PCR), can be used to detect rubella in a throat swab (preferred). Nasal, blood, and urine specimens are also acceptable. Cerebrospinal fluid (CSF) may be tested in cases of suspected rubella encephalitis. Specimens for NAAT should be collected upon first contact with a symptomatic individual. Rubella can be detected by NAAT up to 1 week before and 2 weeks after rash onset. 

Following diagnosis, molecular typing is recommended for epidemiologic purposes. 

Congenital Rubella Syndrome

Infants with suspected CRS can be diagnosed using the same methods as those used for typical cases of rubella (ie, serology and NAAT).

IgM serology is commonly performed by EIA using serum and umbilical cord blood. IgM antibodies can be detected 6-12 months after birth. If IgM results are negative for a sample collected at birth and suspicion for rubella remains high, another sample should be tested after 1 month. 

IgG serology is not routinely useful due to the persistence of maternal antibodies in newborns. However, after maternal antibodies are anticipated to have subsided (between 9 months of age and the time of vaccination), a higher-than-expected IgG titer indicates rubella infection. A two-fold decline in titers each month is typical in uninfected infants.  

NAAT (eg, by RT-PCR) may be performed on a throat, nasal, blood, or urine specimen, which should be collected upon first contact with an infant suspected to have CRS. Throat or urine specimens may provide improved clinical utility in specimens collected later, as viral shedding may continue for a year or more after birth. 

Following diagnosis, molecular typing is recommended for epidemiologic purposes. 

Confirmation of Immune Status

An individual’s immune status can be determined with a single test for rubella-specific IgG antibodies. A positive result indicates protection against rubella. 

ARUP Laboratory Tests

References