US immigration officials insisted the sufferer of an anal infection remove a small piece of medical thread which was being used by doctors to treat the condition. The man required treatment under general anaesthetic as a result.

The man had an anal fistula, which is a painful channel that can develop deep into the anus, caused by infection or digestive conditions such as Crohn's disease. More details, if absolutely necessary, from NHS Direct here.

Arriving on holiday in New York in August last year, the unnamed 48-year-old was interrogated and searched by immigration officers, according to a letter appearing in medical journal The Lancet . The rectal examination discovered a device called a seton, which doctors in the UK had inserted into the fistula to help control long-term infection.

The seton was made of a blue braided medical suture material knotted and passed into the hole where the fistula surfaced. After one baffled immigration officer pulled "very hard" on the seton, the patient was given the choice by the baffled immigration officers of either getting on the next plane home, or submitting himself to a procedure to have it removed.

Happily, as The Lancet's correspondent notes, the curious immigration officer yanking the seton did not damage "the anal sphincter muscles encircled by it".

The seton was duly removed by an airport doctor, who claimed to have no idea what it was. The man now requires treatment under general anaesthetic to have a replacement inserted.

The letter writer concludes by advising seton patients to carry a letter from their doctor when travelling "to the USA or any other country where they are likely to be searched in this manner".

Read the wince-inducing letter here (free registration required). ®