Final answer:
Bacterial infections, especially by Escherichia coli, are the most common cause of infections in the urinary collecting system, with fecal contamination being a primary source of these infections.
Step-by-step explanation:
The most common cause of urinary collecting system infections, which include conditions such as urethritis, cystitis, and pyelonephritis, is bacterial infections. Escherichia coli (E. coli) is specifically noted as the most prevalent bacteria responsible for these infections, primarily in women. The primary mode of infection is often fecal contamination, which occurs due to the anatomical proximity of the anus to the urethra. Good hygiene practices are recommended to minimize the risk of such infections. For men, urinary tract infections may be more often associated with conditions that impair regular bladder emptying like an enlarged prostate, kidney stones, or the use of a urinary catheter.