Risk of toxoplasmic encephalitis in AIDS patients: indications for prophylaxis

To establish the indications for primary prophylaxis against toxoplasmic encephalitis in the Norwegian HIV-positive population, we estimated the incidence of toxoplasmic encephalitis, and related the degree of immunodeficiency and the presence of IgG antibodies against Toxoplasma gondii (T. gondii) to the development of toxoplasmic encephalitis. This retrospective study includes all HIV-positive patients at our hospital from April 1983 to October 1994 (n = 705). A total of 238 patients had AIDS, which represents almost 90% of all AIDS patients in Oslo. Autopsy was done in over 70% of the patients who died during this period; 19 patients developed toxoplasmic encephalitis (8.0%). The median CD4 cell count was 75 x 10(6) cell/I (range 0-280) at the time of diagnosis of toxoplasmic encephalitis. T. gondii serology was studied in 698 (99.0%) of the patients, and was found positive for 17.8%. Of the patients with toxoplasmic encephalitis 18/19 had IgG antibodies against T. gondii and of the 40 AIDS patients who had anti-T. gondii IgG, 18 (45%) developed toxoplasmic encephalitis. We conclude that there is indication for prophylactic treatment of HIV positive patients who have IgG antibodies against T. gondii and who have fewer than 200 x 10(6) CD4 cells/I.