Serological Diagnosis of The Smooth Brucella spp., Brucella canis, and Francisella tularensis in Patients with Overlapping Clinical Features.

This study aimed to serologically diagnose Brucella spp. and Francisella tularensis in patients presenting with overlapping clinical symptoms. A total of 467 serum samples were tested for antibodies against smooth Brucella spp., Brucella canis, and F. tularensis using Rose Bengal Plate Test (RBPT), Serum Agglutination Test (SAT), Microagglutination Test (MAT), and indirect ELISA (iELISA). Seropositivity for smooth Brucella spp. was 12.85% (60/467) by RBPT/SAT and 10.06% (47/467) by iELISA, with moderate agreement (κ = 0.505). The diagnostic titer-based (sole) seropositivity rate was 9.85% (46/467). For B. canis, seropositivity was 5.14% (24/467) by RBPT and 3.64% (17/467) by iELISA, showing substantial agreement (κ = 0.715). The sole seropositivity rate was 3.64% (17/467). For F. tularensis, both MAT and iELISA showed 3.64% (17/467) seropositivity, with moderate agreement (κ = 0.561), while the sole seropositivity rate was 3.43% (16/467). Co-seropositivity was observed in 1.07% (n= 5) of samples between B. canis RBPT and smooth Brucella iELISA, and in 4.07% (n= 19) between smooth Brucella spp. and F. tularensis. One sample (0.21%) was noteworthy, suggesting possible co-infection. These findings confirm the regional presence of brucellosis and tularemia and highlight the value of combining serological methods in patients with non-specific symptoms and low antibody titers.