my son had a small bowel resection where he was rushed into hospital 8 months after with a severe infection where he underwent a laparotomy to find out what the cause of infection was...8 months after this he was rushed in for same type of infection but no surgery was done..they gave him antibiotics for 13 days, no food, ice or water...what is the cause of the infection?

Summarized question: What causes recurrent infections?