Re: “Assessing the Detection of Middle East Respiratory Syndrome Coronavirus IgG in Suspected and Proven Cases of Middle East Respiratory Syndrome Coronavirus Infection” by Alhetheel et al. (Viral Immunol 2017;30:649–653.)

To the Editor:

We read the article on “Assessing the Detection of Middle East Respiratory Syndrome Coronavirus IgG in Suspected and Proven Cases of Middle East Respiratory Syndrome Coronavirus Infection” with great interest (1). Alhetheel et al. concluded that MERS-CoV-IgG testing may not be suitable for diagnosing acute infection or estimating its prevalence during an outbreak (1). We agree that the serological investigation for MERS-CoV might have some problems in diagnosis. Nevertheless, it is still used in some countries due to the less expensive cost comparing with molecular assay. The good example is the use for surveillance in Korea (2). Focusing on the false negative result in the report by Alhetheel et al., the possible cause might be due to several reasons. First, in very early infection, the main immunological response should be IgM, not IgG. Hence, the use of MERS-CoV-IgG test might result in false negative. Second, in case that there is an excessive immunological response to the infection, the prozone effect is possible and this can result in false negative. To manage possible prozone effect by dilution, preparation or EDTA treatment (3) might help improve the diagnostic property of MERS-CoV-IgG test.