Throat swab specimens are the preferred sample for CRS (or CRI) confirmation by RNA detection and for determination of the rubella genotype. However, other samples such as nasal swabs or aspirates, urine, and cerebrospinal fluid (CSF) specimens are acceptable for RNA detection to confirm CRS. Oral fluid samples have proven to be useful for rubella RNA detection from CRS cases [8]. Tissues from biopsy or autopsy may also be used for laboratory confirmation of CRS cases. In CRS cases where cataracts are present, surgically removed cataracts can be submitted for molecular testing. Rubella virus RNA has been detected in cataracts up to three years after birth.
Serologic tests to confirm CRS include the demonstration of rubella IgM antibodies or the demonstration of increasing levels of IgG antibodies in the first year of life [5]. In CRS cases, IgM antibodies are often present shortly after birth, but re-testing should be performed since some infants do not develop antibody for a few weeks. The IgM may remain detectable for up to 1 year although IgM detection is most reliable between 3-6 months of age. For infants beyond 6 months of age, an evaluation of rubella-specific IgG is recommended to confirm CRS [8].
CRS cases can continue to shed virus for up to one year after birth and can be the source of virus for rubella infection in exposed persons, including susceptible pregnant women. Specimens for virus detection should be collected when a case is first suspected. Ideally, specimens should be collected in the first 3 months of age since about 50% of affected infants may not shed virus beyond 3 months of age. Infants with CRS should be monitored until they are at least 1 year of age. Alternatively, demonstration that virus shedding has ceased can be achieved by collection of two clinical specimens obtained one month apart and collected after the infant is older than 3 months of age [9]. Both specimens should have negative culture results.