When I was first diagnosed with reactive arthritis 40 years ago, I was told 3 things could happen. After the infection was treated, the flare of reactive arthritis might only happen once. However flares of reactive arthritis could start to have a recurring pattern. Finally, reactive arthritis could become chronic. Not much was known about reactive arthritis 40 years ago. Treatments are better now.

"Reactive arthritis usually has a self-limited course, and the symptoms resolve within 3 to 5 months. Symptoms lasting beyond 6 months indicate a chronic element of the disease. Sacroiliitis is the most common chronic joint involvement. Patients who are HLA-B27 positive have a higher risk of recurrence of ReA. 15-30% of patients with ReA can develop long-term arthritis or other joint abnormalities. The presence of hip involvement, unresponsiveness to NSAIDs, and ESR greater than 30 portend a worse outcome."
https://www.ncbi.nlm.nih.gov/books/NBK499831/
and
https://www.mayoclinic.org/diseases-conditions/reactive-arthritis/symptoms-causes/syc-20354838
------------------------------------
I was 32 when an enteric infection got the better of me. The nausea, vomiting and diarrhea went away after a few days but then the lower back pain started shortly thereafter. I wasn't hospitalized but the pain was excruciating so I sought out a doctor. I don't think they understood how much pain I had because the medical advice was ibuprofen and a new mattress.

I didn't buy a new mattress but I started taking ibuprofen according to the recommended doses on the label. When ibuprofen didn't help, I went back to the doctor. I was told that I could "safely take" more than the recommended dose on the label and again told that I should invest in a new mattress.

I took as much ibuprofen as I the doctor said I could safely take but that didn't help. I knew my mattress wasn't the problem.

I was probably taking toxic amounts of ibuprofen but it was unclear how much ibuprofen stayed in my stomach. All the nausea, vomiting and diarrhea was awful. Not that much of anything was staying down. What stayed down seemed to exit out the other end rather quickly.

After a month of N-V-D, I was in dire straits but then the retching started. Nothing came up except small amounts of blood. After one particularly long retch I looked at myself in the mirror. I looked like I might die soon.

My right pupil was fully dilated and fixed while my left pupil looked normal in size. My left eye was very red and inflamed like an infection but that didn't matter to me. Never mind an eye infection because I thought maybe I had a stroke. I didn't call 911 . I drove myself to the emergency room which wasn't the best thing to do since it might be a stroke.

I explained everything when I got to the emergency room. A stroke was ruled out in the emergency room because I was too coherent to have a stroke. Labs were drawn and I was severely dehydrated with evidence of an infection. Antibiotics and IV fluids were given. As it turned out my right eye being fully dilated was normal when people retch. My left eye which didn't dilate was a problem. That pupil didn't move at all to light exposure and dark.

After I was stabilized medically, I thought I was going to be admitted but that didn't happen. It was late so I was told to go home and come back first thing in the morning. An outpatient doctor was notified and was expecting me at 8 a.m. It was already after midnight so there wasn't much time for sleep. I went home hoping to survive until morning.

I spent all of the next day in an ophthalmologist's chair. My left eye I was more of a concern than all the pain I had. The ophthalmologist said I had uveitis and I could lose my vision if the inflammation couldn't be stopped.
https://www.mayoclinic.org/diseases-conditions/uveitis/symptoms-causes/syc-20378734
I think it was fortunate that I had uveitis because it made the diagnosis of reactive arthritis easier.
----------------------------
I must have received a hundred eye drops and a handful of little white pills which I later learned was prednisone. It was my first dose of Prednisone but now I have take boatloads of prednisone.

By the end of the day I felt good but I still needed to go back to the medical doctor to address my pain. The medical doctor said I had reactive arthritis and sulfasalazine was started. I was HLA-B27+ but I shouldn't read too much into that. Now it is known that HLA-B27 may contribute to the development of autoimmune diseases.

Fast forward 40 years and I have been diagnosed with multiple autoimmune conditions. Many things have happened in 40 years. According to my current rheumatologist, I have a full range of rheumatology conditions including reactive arthritis.

I finally was able to stop Prednisone a few years ago. Now I take a biolgics called Actemra (tocilizumab) that works well for me.

Biologics like Humira and other TNF-inhibitors probably are used more often for reactive arthritis.

With the gene mutation, your son is at risk for reactive arthritis, and knees are often affected. As to whether it will become long-term is always a question.

There I not a lot of literature about reactive arthritis, but it is covered in this article, about 2/3 or the way down.
https://emedicine.medscape.com/article/1201027-overview#a3
Has he seen a rheumatologist experienced with spondylitis or spondlyoarthropathy? This is an uncommon subset of arthritis and not every doc is familiar with treating it.

The good news is that ther are now some biological available if I doesn't resolve in time.

I'm 50 yr old, female, got food poisoning March 18th of this year that lasted 5 days. Literally 7 days after getting sick, March 25th, my left knee swelled and I had agonizing pain. Still in pain now but not as crazy severe. Pain is still in knee but it's not hot and swollen anymore. Now also have pain in right foot and both wrists. I too am wondering when this might end. I haven't been referred to a rheumatologist yet. I have and appt with my PCP tomorrow talk about what else I can do since NSAIDS and prednisone didn't help. I have a sons and I'm afraid I have the HLA B27 gene and I passed onto them. I'd hate for them to deal with this. It's awful! My job let me switch to full remote until I heal. Otherwise, I'd have a lot more stress! 😩