This block comprises arthropathies due to microbiological agents. Distinction is made between the following types of etiological relationship:

a) direct infection of joint, where organisms invade synovial tissue and microbial antigen is present in the joint;

b) indirect infection, which may be of two types: a reactive arthropathy, where microbial infection of the body is established but neither organisms nor antigens can be identified in the joint, and a postinfective arthropathy, where microbial antigen is present but recovery of an organism is inconstant and evidence of local multiplication is lacking.