Imagine this: You recover from food poisoning or a urinary infection, thinking the worst is over. Then, weeks later, your knee swells like a balloon, your heel throbs, or your eyes turn red and gritty. This puzzling reaction is post-infection arthritis, a case of mistaken identity where your immune system attacks your joints after fighting an infection elsewhere in your body.
Why Does This Happen?
Your immune system is like a highly trained guard dog. After infections caused by common bacteria (like Salmonella, Campylobacter, or Chlamydia), leftover pieces of these germs can accidentally travel to your joints through your bloodstream. When your immune cells detect these “invader fragments,” they launch an attack, causing painful joint inflammation, even though the original infection is long gone.
Key players in this mix-up:
- Bacterial “leftovers”: Bits of bacteria (like proteins or cell walls) hide in joints, tricking your defenses.
- The HLA-B27 gene: Found in 30–50% of people with this condition, this gene makes the immune system more likely to overreact.
- Inflamed tissues: Swelling can affect tendons (like the Achilles), eyes, skin, or the urinary tract.
What Does It Feel Like?
Symptoms usually start 1 – 4 weeks after a gut, urinary, or sexually transmitted infection. You might not even recall the initial illness, 25% of people had no obvious symptoms before joint pain began.
Common signs include:
- Joint pain & swelling: Often in knees, ankles, or feet. Toes/fingers may swell into “sausage digits”.
- Red, gritty eyes: Conjunctivitis occurs in ~30% of cases.
- Urinary discomfort: Burning or frequency, even without an active infection.
- Fatigue and fever: Your body is in overdrive fighting an enemy that’s already left.
Not contagious! While the initial infection can spread between people, the arthritis itself isn’t transmissible.
How Long Does It Last?
For most people, symptoms ease within 3 – 12 months with treatment. But about 20 – 30% develop chronic joint issues, especially if they have the HLA-B27 gene or repeated infections.
Treatment: Calming the Storm
- Goal: Reduce pain and shorten the attack.
- NSAIDs (e.g., ibuprofen): First-line fighters against inflammation.
- Steroids: Prescribed for severe swelling (as pills, creams, or joint injections).
- Antibiotics: Only help if the original infection was Chlamydia and is still lingering.
- Physical therapy: Gentle exercises keep joints moving.
Table: Common Triggers & Timing
| Infection Source | Example Bacteria | Typical Delay Before Arthritis |
| Food Poisoning | Salmonella, Shigella | 1 to 4 weeks |
| STIs | Chlamydia | 2 to 6 weeks |
| Respiratory Illnesses | Mycoplasma | 1 to 3 weeks |
Can You Prevent It?
Maybe! Reducing infection risk lowers your chances:
- Handle food safely to avoid gut bugs.
- Practice safe sex to prevent Chlamydia.
- If you have a family history of arthritis or HLA-B27, stay vigilant after infections.
The Bottom Line
Post-infection arthritis is your immune system’s overzealous “cleanup job” after an infection. While frustrating, it’s usually temporary. If you develop joint pain within a month of diarrhea, a urinary issue, or flu-like illness, see a doctor. Early treatment eases symptoms faster.
