First described by the Egyptians in 1550 BC as “sending forth heat from the bladder,” the urinary tract infection (UTI) is a frequent diagnosis seen in urgent care and doctor’s offices. Burning upon urination, urinary frequency, urinary urgency, smelly urine, and new or changed discharge—these are the hallmarks of a UTI.
Cystitis is an infection of the lower urinary tract. Pyelonephritis is an infection of the kidneys. UTIs affect about 150 million people every year with women greater than men. During any one year, about 10% of women will have a UTI and half of all women will have a UTI in their lifetime. Risk factors include sexual intercourse, diabetes, obesity, female anatomy, and family history. Although sex is a risk factor, UTI is not considered a sexually transmitted disease and a female can get a UTI even when a condom is used. E. coli is the most frequently isolated organism, though other coliform bacteria or yeast could be the culprit.
Most UTIs are caused by bacteria entering the bladder from the urethra. Bacteria then ascending the ureters into the kidneys causes pyelonephritis. Bloodborne pathogens can also lead to pyelonephritis. The urethra is shorter in women so the path to infection is shorter. Use of antibiotics can increase the risk of UTI, probably because the normal flora of the vagina or external urethra in men is disrupted. Indwelling catheterization is also a strong risk factor for UTI from organisms ascending the catheter and the normal complete emptying of the bladder is impossible due to the design of the catheter inlet opening above the balloon. It is estimated that for every day a patient is catheterized with a balloon catheter, the risk of UTI goes up 3-10%. Between the ages of 20 and 50, there is a 50-fold difference between female and male infection rates with that number decreasing over the age 50 and favoring males due to prostate enlargement, decreased bladder emptying, and increased rates of catheterization. Other risk factors are incontinence, poor hygiene, systemic disease, and hospitalization.
The gold standard of diagnosing the uncomplicated UTI is the presence of symptoms and isolation of a pathogen by culture of the urine. In reality, most uncomplicated UTIs are diagnosed clinically and with the aid of the multi-reagent urine dipstick. There are various algorithms used in diagnosis with varying levels of sensitivity (true positive) and specificity (true negative). The presence of nitrite, a product of bacterial respiration, along with leukocyte esterase and/or blood in the urine are strong indicators of a UTI and usually enough to warrant treatment with an antibiotic. For some practitioners worried about overuse of antibiotics and the resulting problems with resistance, a prescription is given with instructions not to start until the culture comes back, usually 48 hours unless symptoms progress.
Gram-negative bacteria often associated with UTIs convert the nitrate in urine to nitrite as part of cellular metabolism. This test isn’t particularly accurate because other organisms (Gram-positive) and yeasts that cause infection do not possess this trait. You can’t hang your hat on this test alone.
Leukocyte esterases are found in certain leukocytes normally associated with bacterial urinary tract infections. They are not found in normal leukocytes, epithelial cells, and bacteria of the healthy urinary tract. Certain conditions like trichomonas, chlamydia, and interstitial cystitis/nephritis can evade detection with this test so it is indicative only.
Blood in the urine can come from trauma (kidney stones) or bacterial mechanisms that lyse red blood cells and so blood can be detected either as whole blood cells or as hemoglobin, the molecule within the cell which has been spilled out by the bacteria. A dipstick positive for blood, nitrite, and leukocyte esterase in addition to one or more patient symptoms (frequency, urgency, pain, or discharge) has a high specificity for a UTI. It’s important to note that the presence of stones is also a risk factor for infection.
A complicated UTI is considered any UTI in a child, presence of a structural or functional urinary tract obstruction, recent urological surgical procedure, or a comorbidity increasing the severity of infection such as uncontrolled diabetes, chronic kidney disease, or the immunocompromised patient.
An uncomplicated UTI is usually treated with a short course of antibiotics such as nitrofurantoin, Trimethoprim/Sulfamethoxazole, or a fluoroquinolone. Some resistance is seen for all of these medications. Complicated UTIs may require longer courses or higher concentrations using the IV route. Many institutions now automatically perform a culture and sensitivity (C&S) when a urinalysis is positive. This identifies the organism (culture) and which antibiotics it is susceptible to (sensitivity).
Pyelonephritis is more serious than cystitis, sometimes necessitating hospital admission. Back pain, fever, malaise, and nausea can accompany kidney infection and this patient often looks and feels very sick. The treatment is a longer course of oral or IV antibiotics along with supportive care. The renal capsule is a tough fibrous material resistant injury. When the kidney is infected, the pressure within the organ rises and it becomes acutely sensitive. One diagnostic test for pyelonephritis is Murphy’s percussive test. One hand is placed over the costovertebral angle of the patient’s back and the other hand thumps it, causing the kidney to vibrate. Pain during this test or immediately afterwards, especially unilaterally, is highly suggestive of pyelonephritis in the patient with flank pain and fever.
If your patient is “sending forth heat from the bladder,” you should definitely do a point of care multi-reagent dipstick and send the urine off for a C&S. Flank pain, costovertebral angle tenderness, and fever should elicit a careful work up and diligent follow up.