Lorraine,
I feel that post-infectious IBS if it is manifesting long after the initial event should be evaluated with a #401-H and OAT. I don’t like to assume that things are all related to something that occurred 1 to 2 years previously. If there are new infections they should be treated accordingly.
IBS occurring shortly after an infection is worthwhile to address via a SIBO approach of digestion support, i.e. enzymes, specific carbohydrate/low FODMAPS diet and motility agents such as Iberogast.
In someone who is constipation doing an herbal bowel cleanse can help clear the symptom picture. The program we like for this is from Dr. Schultz at HerbDoc.com.
Dr. Woeller