RBT
All tests were performed in duplicates. Reagents and quality control samples were allowed to reach to room temperature before use. The RBT (Biomerieux, France) was performed using a validated kit according to the manufacturer’s instruction. The test was performed by thoroughly mixing 30 μL of the test serum or controls with 30 μL of antigen suspension on tear-drop ceramic plate, slowly rocked and incubated for 4 minutes. The presence of agglutination was observed immediately after the incubation.