Brucellosis in Riyadh, Saudi Arabia. A microbiological and clinical study.

During a period of two years, 30 cases of brucellosis were positively diagnosed from a total of 209 patients who reported with prolonged fever for investigation. Diagnosis was made both by blood culture and serological tests. The latter included slide and tube agglutination in all cases and an enzyme linked immunosorbent assay (ELISA) in 16. 11 cases (36.7%) gave negative results by the slide-agglutination screening test used at the recommended single serum dilution of 1:80. This was due to the prozone phenomenon as they gave positive results upon further dilution in the tube agglutination test. 13 of the 16 tested by ELISA were positive for both IgM and IgG and three were positive for IgG only. Of the six cases that were positive by culture, five grew Brucella melitensis and one B. abortus.