Restricted applicability of the polymerase chain reaction for the diagnosis of ocular toxoplasmosis.

The laboratory confirmation of ocular toxoplasmosis has been reported to be facilitated by the polymerase chain reaction (PCR) technique in anterior chamber taps. We utilized PCR specific for a sequence of the Toxoplasma gondii B 1 gene with a length of 194 bp. The sensitivity was adjusted to ten genomic copies per sample in stained gel and two copies after DNA hybridization using a digoxygenin-labeled probe. We amplified DNA from 43 aqueous, 14 serum, and 32 white blood cell (WBC) samples obtained from 31 consecutive otherwise healthy patients with the clinical diagnosis of ocular toxoplasmosis. In the series investigated, 1/43 aqueous samples and 2/32 WBC samples were found to contain detectable amounts of target DNA. An inhibition of the PCR by the aqueous humor as a reason for the low detection rates was excluded. Thus, we conclude that either the sensitivity of aqueous humor PCR is not sufficient for use in the routine diagnosis of ocular toxoplasmosis in immuno-competent individuals or the anterior chamber is not the proper compartment for investigation of this protozoal disease using this approach.