Comment on the Paper by Kamel et al. Entitled ‘Primary Cytomegalovirus Infection in Pregnant Egyptian Women Confirmed by Cytomegalovirus IgG Avidity Testing’

To determine the frequency of primary cytomegalovirus (CMV) infection in pregnant Egyptian women using CMV IgG avidity testing.  A cross-sectional study was conducted at Suez Canal University Hospital, Ismailia, Egypt. A total of 546 pregnant women, presenting for routine antenatal screening, were tested for CMV IgG and IgM using a commercially available enzyme-linked immunosorbent assay (ELISA). Sera from CMV IgM-positive women were tested by CMV IgG avidity assay.  All the 546 pregnant women were seropositive for anti-CMV IgG. Of the 546 women, 40 (7.3%) were positive or equivocal for IgM antibodies. All sera from the 40 women (IgG+/IgM+) showed a high or intermediate CMV IgG avidity index. Of the 40 women, 23 (57.5%) were in the second or third trimesters of pregnancy and had their first-trimester blood retrieved, and the tested CMV IgG avidity assay showed a high avidity index.  Women who were IgM positive had no primary CMV infection in the index pregnancy as evidenced by the high CMV IgG avidity testing.  Thus, testing for IgM, particularly in asymptomatic pregnant women, may frequently create a problem rather that solving it. As primary CMV infections during pregnancy are associated with a high risk of virus transmission to the fetus, discrimination between recent primary and past CMV infection can be an important tool in the clinical management of pregnant women  . Recently, it has been shown that antibody avidity, which is an indirect measure of the tightness of antibody binding to its target antigen, increases in the first weeks after a primary infection. Low-avidity IgG antibodies to CMV persist for up to 20 weeks after a primary CMV infection  . These low-avidity antibodies are then replaced by high-avidity antibodies. Currently, the combination of the presence of anti-CMV IgM antibodies and low-avidity anti-CMV IgG antibodies along with maternal or fetal symptoms is used for the diagnosis of a primary maternal infection [13] . The prevalence of primary maternal CMV infection is not known in Egypt due to factors such as the lack of national screening for CMV to identify those who are seronegative and the absence of an accessible method to identify primary CMV infection. Therefore, in the present study, we aimed to determine the risk of primary CMV infection by using the CMV IgG avidity test in a sample of women from Suez Canal Area, Egypt.  Population and Specimens A cross-sectional descriptive study was conducted from June 2011 to October 2012. Questionnaires were used to gather sociodemographic data. A total of 546 pregnant women who presented for routine antenatal care at the Obstetrics and Gynecology Department, Suez Canal University Hospital, Ismailia, Egypt, were included in this study. Whole blood samples were collected, centrifuged at 2,000 g for 15 min, and sera were removed and stored at –20 ° C. The samples were coded by date of collection and sample number. Ethical approval to perform the study was obtained from the Ethics Committee, Faculty of Medicine, Suez Canal University. Informed consent was obtained from all women prior to the collection of specimens. Serology The CMV IgM and IgG were screened in patients’ sera by using a commercially available capture enzyme-linked immunosorbent assay (ELISA) (CMV IgM and CMV IgG, Dia.Pro; Diagnostic Bioprobes Srl, Italy). Samples with concentrations >0.5 IU/ml (WHO) were considered positive for anti-CMV IgG antibody, whereas samples were considered IgM positive when the ratio of the sample optical density at 450 nm to the cutoff value (signal to cutoff) was >1.2 and were considered equivocal when the ratio was between 1 and 1.2. Any CMV IgM-positive woman was then tested by an IgG avidity assay (VIDAS CMV IgG avidity; BioMérieux, Lyon, France). VIDAS CMV IgG avidity assay (enzyme-linked fluorescent assay, ELFA) consists of two assays with and without 6 M urea to dissociate low-avidity antibodies, which enables weak-avidity antibodies produced at the early stage of a primary infection to be differentiated from high-avidity antibodies, which are characteristic of a former infection. The procedures and interpretation of results were performed according to the manufacturer’s instructions. The avidity index is the ratio of the relative fluorescence value obtained for the sample with the strip containing urea buffer to the relative fluorescence value without urea buffer. On the VIDAS instrument, an avidity index ≥ 0.8 is a strong indicator of a primary infection dating back >3 months, while an index <0.2 is a strong indicator of a primary infection dating back <3 months. An avidity index between 0.2 and 0.8 is not capable of distinguishing a recent from a past infection. ELISA assay results were analyzed in the three trimesters of pregnancy for all women included in the study.

Field of study: Medicine