How does cystitis spread to the kidney?

Upwards,: There is usually some minor degree of reflux of urine up to the ureters from the contracting bladder during voiding. If urine is infected, a spread of infection upwards could take place.

2 ways: 1) bladder reflux, an abnormal condition, allows urine to back up and transport bacteria to kidney. Normal, competent bladder valves can become rigid like pipes with cystitis and become incompetent and allow reflux 2) many bacteria, and particulaly strains of e. Coli have hairlike projections and can crawl through the ureterovesical junction (valve) similar to caterpillars and reach kidney.