Why do some people develop sepsis from urinary infections, and others don't?

Good Q: It varies. Some bacteria are more likely to cause sepsis (systemic infection) than others. Sometimes the patient has immune system issues or poor health that make them more likely to become septic and sometimes an infection, if not treated quickly enough, will progress from a local problem into a systemic one.

Immunity: Some people have good immunity, do not end up in sepsis. It all depends on other comorbidities like diabetes etc.

Multiple factors.: The innate immune system, virulence of the organism, presence of renal stones or abnormal anatomy can all play a part in whether sepsis occurs. Even a persons diet prior to getting sick can make a difference.