Introduction to Urinary Tract Infections

Urinary tract infections (UTIs) can be divided into upper and lower tract infections:

• Upper tract infections involve the kidneys (pyelonephritis).

• Lower tract infections involve the bladder (cystitis)

However, differentiating between the sites of infection may be difficult or impossible. Progression of upper or lower UTIs can lead to urosepsis.

Bacteria cause most cases of cystitis and pyelonephritis, and Escherichia coli is the predominant pathogen.

The most common nonbacterial pathogens that cause UTIs are fungi (usually candidal species) and, less commonly, mycobacteria, viruses, and parasites. Nonbacterial pathogens usually affect patients who are immunocompromised; have diabetes, obstruction, or structural urinary tract abnormalities; or have had recent urinary tract instrumentation.

Of the parasitic infections, only trichomoniasis is common in the United States, and it usually presents as a sexually transmitted infection (STI). Other parasites (eg, filariasis, leishmaniasis, schistosomiasis) can also cause symptoms similar to UTI because of obstruction or other local effects. For example, in systemic visceral leishmaniasis, direct parasitic invasion and immune-mediated kidney damage can occur.

Other than adenoviruses (implicated in hemorrhagic cystitis), viruses have no major contribution to UTI in immunocompetent patients.

Although urethritis and prostatitis can be caused by infections that involve the urinary tract, the term UTI usually refers to pyelonephritis and cystitis. Urethritis is usually caused by an STI (eg, gonorrhea, chlamydia) (1). Prostatitis can be caused by common UTI pathogens (eg, E. coli) and sometimes by common STI pathogens (eg, Neisseria gonorrhoeae).