Validation and Cost-effectiveness of an in-house Complement Fixation Test Using locally prepared biological components Compared with a Commercial CFT for the Diagnosis of Bovine Brucellosis

Document Type : Original Article

Authors

1 Department of Microbiology, Faculty of Veterinary Medicine, Cairo University, Giza 12211, Egypt.

2 Professor of Microbiology, Department of Microbiology, Faculty of Veterinary Medicine, Cairo University, Giza 12211, Egypt.

3 Department of Brucellosis Research, Animal Health Research Institute, Agricultural Research Center, Dokki, Giza 12618, Egypt.

4 Professor, Department of Brucellosis Research, Animal Health Research Institute, Agricultural Research Center, Dokki, Giza 12618, Egypt.

Abstract

This study aimed to develop and validate an in-house Complement Fixation Test (CFT) using locally prepared, titrated, and standardized biological reagents (complement and hemolysin). Diagnostic performance was assessed in comparison with the competitive ELISA (cELISA) and Rose Bengal Plate Test (RBPT), while cost per reaction was compared against a commercial CFT. Between February 2022 and March 2025, blood samples (n = 1265) were collected from private cattle farms in Nile Delta governorates, following reports of late-stage abortions, confirmed human brucellosis cases, and brucellosis seropositive cattle. From these, serum samples (n =119) from bacteriologically confirmed positive and negative cows were used to validate the in-house against the commercial CFT. Diagnostic evaluation revealed that both in-house and commercial CFTs demonstrated superior diagnostic performance, with sensitivity of 91.5%, specificity of 96%, accuracy of 92%, performance index of 187.5, almost perfect kappa agreement (0.810 ± 0.065), positive predictive value (0.99), diagnostic odds ratio (DOR) (258), area under the ROC curve (0.937) at p<0.05, 95% CI, compared with the other immunoassays. The in-house CFT exhibited equivalent diagnostic performance to the commercial CFT, although it displayed 25–50% differences in complement fixation titers (1/4 to 1/128). These variations, however, did not affect the interpretation of positive or negative results. The estimated cost per one in-house CFT reaction was significantly lower than that of the commercial CFT. In conclusion, the in-house CFT matched the diagnostic performance of the commercial assay while substantially reducing cost and dependence on imported reagents. Local production of CFT components ensures sustainable availability, expanding the diagnostic capacity for brucellosis and other infectious diseases in resource-limited settings.

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