A 37-year-old man presents to the office with pain in his right knee joint. He had pain and discomfort in his knee and fever in the last five days. He works in an international bank and frequently travels to Asia and Australia, from where he had returned two weeks ago. There is no significant family history, and he takes no medication. He looks unwell. Temperature is 38.1°C ( 100.5F), the pulse is 90/min, blood pressure is 124/82mmHg. The rest of the systemic examination is normal. His right knee is swollen slightly tender, and there is a small effusion with a slight limitation in flexion. There is no skin rash and no oral mucosal abnormality. Synovial fluid analysis reveals a white blood count of 50,000/mm3 with predominant neutrophils.