[Diagnosis of congenital infection]

In general, congenital diagnosis is based on: a) maternal serologic assays; b) microbiologic study of amniotic fluid or fetal blood sampling; and c) serology in children and microorganism detection by polymerase chain reaction (PCR) or culture. Congenital infections due to cytomegalovirus, herpes simplex, varicella, B19 erythrovirus and toxoplasmosis are usually the result of primary infection in the mother. Therefore, when IgG antibodies are detected before pregnancy, these infections are ruled out. Definitive serologic diagnosis of acute infection in pregnant women requires the demonstration of seroconversion (i.e., from seronegative to seropositive). In these cases, amniotic fluid or fetal blood sampling should be performed to determine the presence of intrauterine congenital infection. Cytomegalovirus, rubella and toxoplasmosis can be diagnosed by detection of specific IgM antibodies in fetal blood. However, PCR in amniotic fluid has replaced conventional prenatal diagnostic techniques, including fetal blood sampling, in the diagnosis of these infections. In the newborn, these infections may be confirmed by measuring IgM specific antibodies. B19 erythrovirus can be detected by PCR in amniotic fluid or fetal blood. Congenital varicella-zoster infection may be diagnosed on the basis of persistence of IgG antibodies after birth. Definitive diagnosis of herpes simplex virus infection requires viral isolation. Swabs or scraping from clinical specimens can be inoculated into susceptible cell lines for isolation.