Overview
The network laboratories in WHO Regions with both measles and rubella elimination targets should consider routinely testing all suspected cases of measles or rubella for both measles and rubella IgM. Depending on the existing epidemiology of rubella and the status of rubella control activities, laboratories in Regions without a rubella elimination target may perform rubella IgM testing to detect rubella infection among suspected measles cases that are detected outside of known measles outbreaks. Since testing all samples for both measles and rubella is often not a feasible option, initial testing of all samples for measles IgM, followed by testing the measles IgM-negative samples for rubella IgM provides an alternative strategy.
Detection of measles- or rubella- specific immunoglobulin M (IgM) in a single serum specimen is the standard method for the rapid laboratory confirmation of measles and rubella. However, oral fluid (OF) is an alternative sample for IgM detection that offers a minimally invasive collection method and may offer reduced cost for transportation. Serum (or OF) specimens tested from individuals with a rash illness due to causes other than measles and rubella may produce false positive IgM results in measles- or rubella-specific IgM EIAs, a problem that may be encountered regardless of the IgM assay used. This is especially true in settings with low prevalence of disease, since no test is 100% specific. Guidance for additional testing to address the lower predictive value of positive IgM results in elimination settings is discussed in Chapter 8. Laboratory testing in support of measles and rubella surveillance in elimination settings.
Although not used for routine diagnosis of measles and rubella infection, assays that measure virus-specific IgG by EIA may aid in case classification (section 4.5). The measurement of measles and rubella IgG for assessing population immunity in serosurveys is covered in Chapter 9. Laboratory testing for determination of population immune status. Commercial kits that measure the avidity of rubella virus-specific IgG antibody are widely available and may be utilized as an additional test in certain situations (section 4.6).