Clinical Significance of IgG avidity testing and other considerations in the diagnosis of congenital cytomegalovirus infection

Human cytomegalovirus (CMV) is a member of the herpesviridae family. It is a double stranded, enveloped and ubiquitous DNA virus that rarely causes disease in healthy individuals yet can cause serious diseases in the fetus and in immunosuppressed individuals [1]. Most CMV infections are inapparent, but the virus can cause a wide range of diseases in susceptible individuals. Fetal CMV infection is of great public health concern because it is the most common cause of congenital infection worldwide, affecting 0.2% to 2.4% of all live births [2]. The overall birth prevalence of congenital CMV infection was reported to be 0.64% but varied considerably among different study location [3]. CMV is now the most common viral cause of mental retardation and hearing deficit of children in developed countries [4]. It causes deformation of preformed tissues rather than malformation of developing organs [4], so CMV can affect fetuses beyond the first trimester, although earlier primary infection is usually more severe [5]. Primary infection is defined as CMV infection in a previously seronegative person. Secondary infection is defined as intermittent excretion of the virus in the presence of host immunity and may be due to either reactivation of an endogenous virus [4, 5] or exposure to a new virus strain from an exogenous source [4]. Primary maternal infection is most likely to cause severe symptomatic congenital infection [4, 5] but recurrent infection may also rarely do so. Perinatal CMV infection is usually not associated with clinical illness in term babies, but may also cause serious problems in preterm infants. [4, 5].