[Influence of standardization upon the results of serological analysis of toxoplasmosis (author's transl)].

It is the purpose of this paper to determine whether the decline of the serologically verified acute Toxoplasma gondii infections observed since the late sixties and found in literature has been caused by epidemiological factors or whether the standardization of serological methods (10) introducted in 1966/66 for the determination of antibodies specific to Toxoplasma gondii has been responsible. The paper is based on material of the prospective study, "Pregnancy and child development" supported by the Deutsche Forschungsgemeinschaft (DFG). Mainly six laboratories did the serological analysis for antibodies against T. gondii from 1964 to 1970. The following results were obtained: 1. Laboratories using the standardization observed a decline of the highly positive dilution starting in 1968 (Fig. 1, Table 1). 2. The proportion of the samples positive in the dye test did not change (Fig. 1). 3. The proportion of sera reacting in the complement fixation test (CFT) with a dilution of 1:5 increased. But after introduction of the standardization more sera were analyzed by both the dye and complement fixation tests than before (Table 2, Fig. 2). 4. The proportion of sera found positive by the complement fixation test increased slightly up to 1968 (Fig. 3). 5. Differences in the age structure (Fig. 4) or dietary habits of the group (Fig. 5) did not cause the changes in titer. 6. Therefore the standardization was introduced a considerable proportion of the sera showing dye test results of more than 1:1000 reacted negatively to the complement fixation test (Table 4). These cases were probably not acute infections. 7. When the standardization was introduced the difference between results of first and second analysis decreased for sera with titers smaller then 1:256 (increased of reliability) (Table 5, Fig. 7). 8. Complement fixation titer show an analogous behavior. (Table 7 and 8). The results detained above show that the decrease, observed since 1969, of the cases of acute Toxoplasma infections verified by serological methods is not caused by epidemiological but rather by methodical factors.