My knee swelled up a few weeks after a stomach bug. Are they connected?

What reactive arthritis is

After certain infections, such as food poisoning with salmonella or campylobacter, or some sexually transmitted or urinary infections, the immune system can go on to inflame the joints even though the original germs have cleared. The knee is one of the most common joints affected, along with the ankles and feet.

It is more common in young adults, and people who carry a gene called HLA-B27 are more susceptible. Travellers who had a stomach upset on holiday sometimes return to Doha with a swollen knee a few weeks later.

Symptoms you might notice

• A swollen, stiff knee, sometimes both knees or an ankle too
• Pain at the heel or where tendons attach to bone
• A swollen "sausage" toe or finger
• Red, gritty eyes
• Burning when passing urine
• Lower back or buttock pain that is worse in the morning

How it is checked

The main priority is to make sure the knee itself is not infected. A sample of fluid is usually drawn from the knee and tested for bacteria and crystals. Blood tests look at inflammation markers and sometimes HLA-B27, and a stool or urine test may be done if the triggering infection is still active.

The diagnosis is built from the timing, the pattern of joints and the exclusion of other causes, as there is no single test that proves reactive arthritis.

Treatment and outlook

Most people are treated with anti-inflammatory medicines, rest from impact activity and gentle movement to keep the knee from stiffening. A steroid injection into the knee can help a persistently swollen joint once infection is ruled out. If the original infection is still present it is treated with antibiotics.

Many cases settle over three to six months. A minority have recurring or longer-lasting symptoms and are usually looked after jointly with a rheumatologist. At Aman Hospital in Doha, Dr. Gelber assesses the knee, aspirates it when needed and coordinates that referral.