A 32 year old man presented from the airport at 16.00 hrs. He said he had attended the walk-in centre before checking-in to a flight for Bangkok. He had banged his knee 3 days before, while getting off a motorcycle. The knee had swelled up on the way to the airport. He wanted to have the effusion drained.

On direct questioning he admitted that he was actually on his way back from Bangkok. He had been on a sex holiday, and not for the first time. A previous HIV test was negative.

On examination he was in pain and he had a tense swollen effusion. Aspiration of the effusion produced a thick yellow fluid.