Rubella Surveillance and Diagnostic Testing among a Low-Prevalence Population, New York City, 2012–2013

Abstract

The New York City Department of Health and Mental Hygiene (DOHMH) receives clinical and laboratory reports for rubella. Because rubella immunoglobulin M (IgM) assays may produce false-positive results and rubella infections may be asymptomatic, interpretation of positive IgM results can be challenging. Rubella reports received by DOHMH in 2012 to 2013 were reviewed. The rubella IgM testing purpose was determined through case investigation. Results of IgM testing by indirect enzyme-linked immunosorbent assay (ELISA) and capture enzyme immunoassay (EIA) were compared to determine positive predictive value (PPV) and specificity. DOHMH received 199 rubella reports; 2 were true cases. Of all reports, 77.9% were tested for rubella IgM erroneously, 19.6% were tested for diagnostic purposes, 2.0% had unknown test purpose, and 0.5% were not tested. PPV of indirect ELISA was 6% overall, 14% for diagnostic tests, and 0% for tests ordered erroneously. PPV of capture EIA was 29% overall, 50% for diagnostic tests, and 0% for tests ordered erroneously. Overall, specificity was 52% for indirect ELISA and 85% for capture EIA. Limiting rubella IgM testing to patients for whom rubella diagnosis is suspected and using a more specific IgM assay have the potential to reduce false-positive rubella IgM results.

ISUOG Practice Guidelines: role of ultrasound in congenital infection

“…Rubella-specific IgG is usually present within a week after the onset of the rash. IgM levels rise early but IgM assays have a 15-50% false-positive rate 146 , which may be related to cross-reactivity with other viruses, long-term persistence after vaccination or even the presence of autoantibodies 147,148 . Therefore, the diagnosis of acute rubella infection should not rely on a positive IgM test alone, but should also take into account the history of relevant exposure, development of a rash, history of vaccination and results of previous rubella testing 146 .…”

“…IgM levels rise early but IgM assays have a 15-50% false-positive rate 146 , which may be related to cross-reactivity with other viruses, long-term persistence after vaccination or even the presence of autoantibodies 147,148 . Therefore, the diagnosis of acute rubella infection should not rely on a positive IgM test alone, but should also take into account the history of relevant exposure, development of a rash, history of vaccination and results of previous rubella testing 146 . Similar to other viral testing, rubella IgG avidity can help to determine the timing of infection; high avidity usually indicates infection occurring more than 3 months earlier [149][150][151] , while low-avidity antibodies are usually associated with infection within the previous 3 months.…”

Pitfalls of rubella serology while on the brink of elimination: evaluation of national data, Belgium, 2017

“…Only two cases were confirmed, so the PPV was very low, supporting the results of the Ontario study. The New York study concluded that limiting rubella testing to patients with a clinical suspicion of infection has the potential to reduce false-positive rubella IgM results [ 25 ].…”

Rubella virus-specific humoral immune responses and their interrelationships before and after a third dose of measles-mumps-rubella vaccine in women of childbearing age

“…The rubella-specific IgG avidity was measured using the Zeus Rubella IgG ELISA Test System (Zeus Scientific Inc.; Branchburg, NJ) described above, with the following modifications [25]. All serum samples at or above 10 IU/mL were tested.…”