<s>[INST] context: This patient developed enteritis-associated arthritis affecting the lumbar and sacroiliac joints several weeks after Shigella dysentery. He subsequently developed conjunctivitis and, most likely, uveitis. This symptom complex is a classic representation of a cluster of related disorders called seronegative spondyloarthropathies. This cluster includes ankylosing spondylitis, reactive arthritis, psoriatic arthritis, and enteropathic arthritis (as in this case). A common feature is a very strong association with the HLA-B27 genotype. Despite some similarities with rheumatoid arthritis, these patients invariably have a negative test result for rheumatoid factor. Urethritis caused by Chlamydia trachomatis can trigger reactive arthritis, another form of seronegative spondyloarthropathy. Such infection precedes the onset of arthritis, however. There is no relationship between infection with Borrelia burgdorferi, the causative agent of Lyme disease, and reactive arthritis in individuals testing positive for HLA-B27. Similarly, Epstein-Barr virus infection is not a trigger for these disorders. [/INST] question: A 30-year-old man has had cramping abdominal pain and bloody diarrhea for the past 4 days. On physical examination, there is diffuse tenderness on palpation of the abdomen. Bowel sounds are present. There are no masses and no organomegaly. A stool culture is positive for Shigella flexneri. The episode resolves spontaneously within 1 week after onset. Six weeks later, he has increasingly severe lower back pain. Physical examination now shows stiffness of the lumbar spine and tenderness of the sacroiliac joints. He is treated with nonsteroidal anti-inflammatory agents. Two months later, the back pain recurs, and he complains of redness of the right eye and blurred vision. Serologic testing for which of the following is most likely to be positive in this patient? | options: A: Borrelia burgdorferi B: Chlamydia trachomatis C: Epstein-Barr virus D: HLA-B27 | answer: D </s>