Positive Predictive Value of IgM Detection in Diagnosis of Acute Rubella Infection

Rubella vaccination is essential due to the relationship between the primary infection and congenital abnormalities. Detection of IgM is the most common method of diagnosing acute rubella infection. In Iran, no rubella outbreak has been reported after the global vaccination; although positive rubella IgM cases have been detected. Approaching elimination of a viral infection, its incidence rate and the positive predictive value (PPV) of the diagnostic test would be reduced. Recently, adequate vaccination coverage leads to a reduction in rubella incidence, in such a situation this study estimated the PPV of rubella specific IgM. Serum samples from cases with fever and rash, during three tandem years were collected from all over the country. To evaluate the PPV of IgM detection in acute rubella infection diagnosis, all the sera were subjected to IgM detection, then all IgM positive cases were evaluated via IgG avidity assay. The PPV of IgM detection test to detect acute rubella infection was 15.8%. In conclusion, giving the appropriate immunization coverage in the country, the PPV of detecting rubella IgM was low. Therefore, diagnosis of acute rubella infection should not be confirmed only based on IgM positive result.