Human brucellosis in the State of São Paulo: a serological survey

Abstract

The authors using the Castañeda brucella slide agglutinantion test, performed an inquire in São Paulo, Brazil. The blood of four groups of patients was tested: 1) with clinical diagnosis of brucellosis (170); 2) with clinical diagnosis of infectious disease, not suspected of brucellosis (1825); 3) samples for lues diagnosis (11.152); 4) slaughter-house workers (30). The antigen used, was prepared according to Castañeda rapid antigen, colored with methylene blue. This antigen was built in such a way that it will agglutinate sera with a tube title as weak as 1/10 and was used for screening test. The same antigen, without the dye, was used for tube agglutination. Blood cultures (Castañeda method) were performed in 23 blood specimens. Considering a tube title of 1/100 as indicative of brucellosis our results may be resumed as follows: Comparing agglutination title between group 1 (3,53%) and groups 3 (0.003) we may conclude that: 1) with our technic positive reactions will occur excepcionally in the supposed normal group; 2) clinical diagnosis and serum agglutination run in paralel (X² = 9.350 P = 0.002); 3) higher incidence of positive reactions in group 2 shows clearly that brucellosis may simulate another infectious diseases. We may conclude that: 1) the higher incidence of a low blood title in patients which clinical diagnosis of brucellosis is statisticully significant if we compare with group 3 (X² = 42.5117 ~P <0.001) and group 2 (x2 = 14.399 P <0.001). We may assume that even a positive reaction in low title must be caused by brucella infection previous or actual. 2) There is not any statistical difference between groups 2 and 3 (X² = 2.131 P = 0.145). If these reactions were inespecific, probably they would occur in the same proportion in all different groups. The similarity of incidence between groups 2 and 3 shows clearly that agglutinations in low title are not due to anamnestic reaction. Blood culture was realized in 23 patients and only one time we were able to recover the brucella organism identified as B. suis. Although the native cattle presents the brucellosis in a high degree, being the chief source of infection in man, the incidence of the disease is very low in humans. This is explained by the fact that the brucellosis in cattle, caused by Brucella obortus, is of low pathogenicity for the human being. All cases of human brucellosis diagnosed in S. Paulo with positive hemoculture for B. suis prove that the infection found is almost exclusively a professional disease. The pasteurization or the simple boiling of the milk, a common use of population, are of a great importance in the prevention of the disease in man.