Urinary tract infections (UTIs) can be divided into upper tract infections, which involve the kidneys (pyelonephritis Acute pyelonephritis Bacterial urinary tract infections (UTIs) can involve the urethra, prostate, bladder, or kidneys. Symptoms may be absent or include urinary frequency, urgency, dysuria, lower abdominal pain... read more ), and lower tract infections, which involve the bladder (cystitis Cystitis Bacterial urinary tract infections (UTIs) can involve the urethra, prostate, bladder, or kidneys. Symptoms may be absent or include urinary frequency, urgency, dysuria, lower abdominal pain... read more ), urethra (urethritis Urethritis Bacterial urinary tract infections (UTIs) can involve the urethra, prostate, bladder, or kidneys. Symptoms may be absent or include urinary frequency, urgency, dysuria, lower abdominal pain... read more ), and prostate (prostatitis Prostatitis Prostatitis refers to a disparate group of prostate disorders that manifests with a combination of predominantly irritative or obstructive urinary symptoms and perineal pain. Some cases result... read more ). However, in practice, and particularly in children, differentiating between the sites may be difficult or impossible. Moreover, infection often spreads from one area to the other. Although urethritis and prostatitis are infections that involve the urinary tract, the term UTI usually refers to pyelonephritis and cystitis.
Bacterial urinary tract infections Bacterial Urinary Tract Infections Bacterial urinary tract infections (UTIs) can involve the urethra, prostate, bladder, or kidneys. Symptoms may be absent or include urinary frequency, urgency, dysuria, lower abdominal pain... read more cause most cases of cystitis and pyelonephritis. The most common nonbacterial pathogens are fungi Fungal Urinary Tract Infections Fungal infections of the urinary tract primarily affect the bladder and kidneys. (See also Introduction to Urinary Tract Infections [UTIs].) Species of Candida, the most common cause... read more (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.
Other than adenoviruses (implicated in hemorrhagic cystitis), viruses have no major contribution to UTI in immunocompetent patients.
The predominant parasitic causes of UTIs are filariasis Bancroftian and Brugian Lymphatic Filariasis Lymphatic filariasis is infection with any of 3 species of Filarioidea. Acute symptoms include fever, lymphadenitis, lymphangitis, epididymitis, and funiculitis (inflammation of the spermatic... read more 
, trichomoniasis Trichomoniasis Trichomoniasis is infection of the vagina or male genital tract with Trichomonas vaginalis. It can be asymptomatic or cause urethritis, vaginitis, or occasionally cystitis, epididymitis... read more , leishmaniasis Leishmaniasis Leishmaniasis is caused by species of Leishmania. Manifestations include cutaneous, mucosal, and visceral syndromes. Cutaneous leishmaniasis causes painless chronic skin lesions ranging... read more 
, malaria Malaria Malaria is infection with Plasmodium species. Symptoms and signs include fever (which may be periodic), chills, rigors, sweating, diarrhea, abdominal pain, respiratory distress, confusion... read more 
, and schistosomiasis Schistosomiasis Schistosomiasis is infection with blood flukes of the genus Schistosoma, which are acquired transcutaneously by swimming or wading in contaminated freshwater. The organisms infect the... read more 
. Of the parasitic diseases, only trichomoniasis is common in the US, usually as a sexually transmitted infection (STI).
Urethritis is usually caused by an STI Overview of Sexually Transmitted Infections Sexually transmitted infection (STI) refers to infection with a pathogen that is transmitted through blood, semen, vaginal fluids, or other body fluids during oral, anal, or genital sex with... read more . Prostatitis Prostatitis Prostatitis refers to a disparate group of prostate disorders that manifests with a combination of predominantly irritative or obstructive urinary symptoms and perineal pain. Some cases result... read more is usually caused by a bacterium and is sometimes caused by an STI.
