Guidelines For The Diagnosis Of Congenital Toxoplasmosis In A Neonate Or Young Infant

Table 2 describes the diagnostic workup of an infant suspected of having congenital toxoplasmosis. The practitioner should have a high index of clinical suspicion for congenital infection when confronted with the following scenarios: (1) symptomatic neonatal disease consistent with congenital toxoplasmosis, (2) a history of documented primary maternal T. gondii infection during pregnancy, or (3) a history of HIV1 co-infection when the mother has had either reactivated clinical toxoplasmosis (cerebritis or chorioretinitis) during pregnancy or is profoundly immunosuppressed. Infants born to chronically infected mothers who are similarly immunosuppressed for another reason may also be at risk for congenital infection. All at-risk infants should be evaluated to document or rule out congenital infection and assess the degree of involvement.

At-risk infants who present during the neonatal period should have a complete diagnostic workup as the chances of isolating the organism are best during the first several days of life. Congenital infection is highly likely if the organism is detected and the assays for Toxoplasma IgM, IgA, or IgE are positive. Repeat testing of all infants with reactive Toxoplasma IgM, IgA, or IgE should be done to confirm the presence of congenital infection. Follow-up serological testing of all infants who are strongly suspected of having a congenital infection and are nonreactive in these assays should also be done in case the synthesis of Toxoplasma-specific antibodies is delayed until 3-4 months of age. This delay may occur as a result of late transplacental transmission, the presence of circulating maternal antibody, or concomitant anti-Toxoplasma therapy. Congenitally infected infants with perinatally acquired HIV-1 infection may not be able to synthesize any Toxoplasma-specific antibodies if they have rapidly progressive HIV-1 disease. In these last cases, the diagnosis may have to rely on the detection of the organisms or the presence of the typical clinical and radiologic findings.

Table 2

Guidelines for the Diagnosis of Congenital Toxoplasmosis in a Neonate or Young Infant

I. Clinical evaluation

History and physical examination including a neurological and ophthalmologic examina tion, which must include fundoscopy Auditory testing (brain stem response to 20 dB)

II. Non-specific laboratory evaluation

Laboratory: Complete blood cell count with differential and platelet count; serum quanti tative immunoglobulins; liver function tests, including 7GTP and bilirubin; urinalysis, serum creatinine; CSF cell count; protein; and glucose Radiologic: Brain computed tomographic scan with and without contrast; chest x-ray

III. Toxoplasma-specific laboratory evaluation

1. Serologic: Toxoplasma-specific IgG and IgM: IgM ISAGA or DS-ELISA are preferred IgM assays because of superior sensitivity (~80 and 75%, respectively)3; Sabin-Feldman dye test ideally is used for IgG (although most laboratories use ELISA assays)

2. Other serologic assays: IgA DS-ELISA, IgE ISAGA/ELISA may also be useful for diagnosis6

3. CSF serology: Obtain T. gondii-specific IgG and IgM antibodies

4. Isolation/detection of the organism:

a. Inoculate into mice or tissue culture samples from placenta, umbilical cord, or infant blood b. Test amniotic fluid (if available), infant blood, and CSF for T. gondii deoxyribo-nucleic acid using PCR

Modified with permission from ref. 1.

"Commercially available EIA assays for T. gondii IgG and IgM are useful for detecting acquired infec tion; they are less sensitive for detection of congenital infection. If an IgM EIA is equivocal or negative and there is a high index of suspicion for congenital infection, serum should be sent to a reference laboratory for serum IgG testing or other antibody testing.

6The same test should be performed using maternal serum and the IgM ELISA can be substituted for the ISAGA; on maternal serum, the IgG agglutination AC/HS assay should also be obtained.

The diagnosis of congenital infection among infants who present beyond the neonatal period rests primarily on the demonstration of a repeatedly positive Toxoplasma IgM, IgA, or IgE and a persistently positive or rising Toxoplasma IgG titer.

0 0

Post a comment