The latest review in our Clinical Practice series comes from Dr. Thomas Hooten at the University of Miami Miller School of Medicine.
Urinary tract infection is the most common bacterial infection encountered in the ambulatory care setting in the United States, accounting for 8.6 million visits in 2007. The self-reported annual incidence of urinary tract infection in women is 12%, and by the age of 32 years, half of all women report having had at least one urinary tract infection.
• What are the risk factors for uncomplicated sporadic and recurrent cystitis and pyelonephritis?
Risk factors for uncomplicated sporadic and recurrent cases of cystitis and pyelonephritis include sexual intercourse, use of spermicides, previous urinary tract infection, a new sex partner (within the past year), and a history of urinary tract infection in a first-degree female relative. Case-control studies have shown no significant associations between recurrent urinary tract infection and precoital or postcoital voiding patterns, daily beverage consumption, frequency of urination, delayed voiding habits, wiping patterns, tampon use, douching, use of hot tubs, type of underwear, or body-mass index.
• Which organisms cause the majority of uncomplicated cystitis and pyelonephritis in women?
In women, E. coli causes 75 to 95% of episodes of uncomplicated cystitis and pyelonephritis; the remaining cases are caused by other Enterobacteriaceae, such as Klebsiella pneumoniae, and gram-positive bacteria such as Staphylococcus saprophyticus, Enterococcus faecalis, and Streptococcus agalactiae (group B streptococcus). However, the latter two organisms, when isolated from voided urine from women with uncomplicated cystitis, often represent contamination of the voided specimen.
Morning Report Questions
Q: What are the classic symptoms of cystitis versus pyelonephritis and how does one approach the diagnosis?
A: Cystitis is usually manifested as dysuria with or without frequency, urgency, suprapubic pain, or hematuria. Clinical manifestations suggestive of pyelonephritis include fever (temperature >38 degrees C), chills, flank pain, costovertebral-angle tenderness, and nausea or vomiting, with or without symptoms of cystitis. Dysuria is also common with urethritis or vaginitis, but cystitis is more likely when symptoms include frequency, urgency, or hematuria; when the onset of symptoms is sudden or severe; and when vaginal irritation and discharge are not present. The only finding on physical examination that increases the probability of urinary tract infection is costovertebral- ngle tenderness (indicating pyelonephritis). Results of a dipstick test for leukocyte esterase or nitrites provide little useful information when the history is strongly suggestive of urinary tract infection, since even negative results for both tests do not reliably rule out the infection in such cases. A urine culture is indicated in all women with suspected pyelonephritis but is not necessary for the diagnosis of cystitis. Studies have shown that the traditional criterion for a positive culture of voided urine (10(5) colony-forming units [CFUs] per milliliter) is insensitive for bladder infection, and 30 to 50% of women with cystitis have colony counts of 10(2) to 10(4) CFUs per milliliter in voided urine. Since most clinical laboratories do not quantify bacteria below a threshold of 10(4) CFUs per milliliter in voided urine specimens, a culture report of “no growth” or “less than 10,000 CFU” in a woman with urinary symptoms should be interpreted with caution.
Q: How should episodes of recurrent cystitis be treated?
A: Episodes of cystitis that occur at least 1 month after successful treatment of a urinary tract infection should be treated with a first-line short-course regimen. If the recurrence is within 6 months, one should consider a first-line drug other than the one that was used originally, especially if trimethoprim-sulfamethoxazole was used, because of the increased likelihood of resistance. The authors’ recommendations for first-line therapy include nitrofurantoin, trimethoprim-sulfamethoxazole, fosfomycin, and pivmecillinam. Urinary symptoms that persist or recur within a week or two of treatment for uncomplicated cystitis suggest infection with an antimicrobial-resistant strain or, rarely, relapse. In such women, a urine culture should be performed, and treatment initiated with a broader-spectrum antimicrobial agent, such as a fluoroquinolone.