Urinary tract infection is an extremely common disease. In fact, it is the second most common type of infection in humans (respiratory tract infection is number one).

Let’s take a few minutes to review the epidemiology, pathophysiology and treatment of this disease.

Overall, urinary tract infections (UTIs) are much more common in women than in men. This is largely due to the shorter length of the female urethra. This holds true at most ages except in elderly populations, where the UTI rate in males approaches that of females of the same age. Other groups of patients at increased risk of developing UTIs are elderly people, patients with catheters, and people with urinary tract malformations (like incomplete ureterovesical valve closure).

It’s really easy for bugs to get up into the urinary tract, because the epithelium lining the urethra is continuous with the external skin. Add any sort of structural abnormality, like kidney stones, or obstructions (like prostatic hypertrophy), and you’ve got the potential for retaining urine (never a good idea – much better to have a nice constant flow of urine so that even if bugs do get in, they get flushed away). Kidney stones can also act as a nidus for infection, if the stones are colonized by bacteria. Makes it pretty hard to get rid of the infection when you’ve got a constant source.

Most “uncomplicated” UTIs (regular, run-of-the mill infections that are not related to things like structural abnormalities, prolonged antibiotic use, or catheterization) are due to E. coli. E. coli, as you know, is gram-negative bug that lives in the colon. Not surprising that it commonly affects the nearby urinary tract. Complicated UTIs, on the other hand, are usually caused not by E. coli but by other bugs like Proteus, other enterobacteriaceae, Staph and Strep. You can also see non-bacterial UTIs (with organisms like candida) but these are much less common.

There are two additional associations that you should know about for boards (and real life). First: people with Proteus infections are more likely to get renal stones. Proteus has urease, which raises the pH of the urine, making stone formation more likely. Second, young women with uncomplicated UTIs have an increased incidence of Staph saprophyticus infection. E. coli is still the most common bug – but Staph saprophyticus is pretty common too. That’s important to remember because one of the parameters that you look at when evaluating for a UTI is nitrites. Most gram negative organisms (like E. coli) reduce nitrates to nitrites – so the little nitrite square on the urinary dipstick will be positive in most normal UTIs. Gram positive organisms (like Staph) generally don’t reduce nitrates – so the nitrites will not be increased in these infections. You wouldn’t want to only use that parameter to diagnose UTIs, obviously!

Most run-of-the-mill UTIs are treated presumptively with an antibiotic that hits gram-negative bugs. If this doesn’t work, or if the patient is having repeated UTIs, then a culture and sensitivity will be performed and antibiotic therapy adjusted accordingly. Most UTIs go away nicely – but sometimes, the infection can ascend into the kidney, causing pyelonephritis. That’s a whole different story – instead of (or in addition) to the UTI symptoms of burning and urgency, patients get systemic symptoms (like fever) and are at risk for bacteremia (not good). These infections are treated more aggressively – perhaps even with intravenous antibiotics if the infection is serious enough. Better to catch it at the UTI stage if possible!

The image above is part of Andy Warhol’s “Oxidations” series, created in 1978. The series consists of elegant, abstract paintings created in a unique manner: Warhol and others urinated on canvases prepared with copper and bronze metallic pigments that oxidized as the painting dried.

Warhol paid his friend Victor Hugo (not the 19th century poet) to come to his Factory to urinate on canvases primed with copper-based paint. The uric acid in the urine oxidized the metal in the copper ground, forming patterns that bloomed across the copper surface. Warhol also asked one of his Factory assistants to help create the paintings. According to Warhol, his assistant took a lot of Vitamin B, which caused the copper pigment to oxidize to a particularly “pretty color.”

The Oxidations series is said to be a metaphor for transubstantiation, symbolizing the transformation of base materials into precious objects. Art critic Bruce Hainley writes: “Like blood, urine is rich in DNA. The Oxidations are portraits of Victor. They’re also self-portraits and portraits of assistant Ronnie Cutrone. Doggedly marked territories, they trace signs of identity, even if that identity is unknown (or unknowable).”

Andy Warhol may have interpreted his series more simply. In Art/Criticism, he observes: “I read an article on me once that described my machine-method of silk-screening copying and painting – “˜What a bold and audacious solution, what depths of the man are revealed in this solution!’  What does that mean?”

Warhol summed it up best when he said, in Art, “Art is what you can get away with.”