Urinary Tract Infections: Introduction
Urinary tract infections (UTIs) are among the most common bacterial infections encountered in medicine. Accurately estimating incidence is difficult because UTIs are not reportable, but estimates range from 650,000 to seven million office visits per year.
A UTI is defined by urologists as any infection involving the urothelium, which includes urethral, bladder, prostate, and kidney infections. Some of these are diseases that have been clearly characterized (eg, cystitis and pyelonephritis), whereas others (eg, urethral and prostate infections) are not as well understood or described.
The terms simple UTI and uncomplicated UTI are often used to refer to cystitis. In this chapter UTI is used to refer to any infection of the urinary tract, and cystitis is used to specify a bladder infection. The generic term complicated UTI is often used to refer to cystitis occurring in a person with preexisting metabolic, immunologic, or urologic abnormalities, including kidney stones, diabetes, and AIDS, or caused by multidrug resistant organisms.
Asymptomatic bacteriuria, uncomplicated cystitis, complicated cystitis, two urethral syndromes, four prostatitis syndromes, and pyelonephritis are discussed in this chapter. Although separated into different diagnoses, differentiating among syndromes and deciding treatment is left to the clinician’s discretion.
Antibiotic resistance is a topic that has been left mostly to the reader. General recommendations about specific antibiotics are inappropriate, given that antibiotic resistance differs from location to location. It is the responsibility of the individual physician to be familiar with local antibiotic resistances, and to determine the best first-line therapies for his or her practice. Always keep in mind that antibiotic use breeds resistance, and try to keep first-line drugs as simple and narrow-spectrum as possible.
Asymptomatic Bacteriuria
- Asymptomatic patient.
- Urine culture with more than 105 colony-forming units (CFU); bacteria in spun urine; or urine dipstick analysis positive for leukocytes, nitrites, or both.
Asymptomatic bacteriuria is defined separately for men, women, and the type of specimen. For women, clean-catch voided specimens on two separate occasions must contain more than 105 CFU/mL of the same bacterial strain or one catheterized specimen must contain more than 102 CFU/mL of bacteria. For men, a single clean-catch specimen with more than 105 CFU/mL of bacteria or one catheterized specimen with more than 102 CFU/mL of bacteria suffices for the diagnosis. By definition, the patient must be asymptomatic; that is, he or she should not be experiencing dysuria, suprapubic pain, fever, urgency, frequency, or incontinence. Screening for bacteriuria does not need to be done in young, healthy, nonpregnant women; elderly healthy or institutionalized men or women; diabetic women; persons with spinal cord injury; or catheterized patients while the catheter remains in place.
Pregnant women are now the only group that should be routinely screened and treated for asymptomatic bacteriuria. There are multiple guidelines recommending screening of this group of patients. Screening should occur between 12 and 16 weeks’ gestation. The incidence is approximately 2%-10% of pregnant women. There are numerous studies showing an association between asymptomatic bacteriuria and premature birth, low-birth weight, and a high incidence of pyelonephritis. In the United States, screening is usually done by urine culture because dipstick screening can miss patients without pyuria or with unusual organisms.
Treatment should be guided by local rates of resistance. The usual first-line treatment in the absence of significant resistance or penicillin allergy is a 7-day course of amoxicillin. Nitrofurantoin or a cephalosporin is suggested for penicillin-allergic pregnant patients, again for 7 days.
Uncomplicated Bacterial Cystitis
- Dysuria.
- Frequency, urgency, or both.
- Urine dipstick analysis positive for nitrites or leukocyte esterase.
- Positive urine culture (>104 organisms).
- No vaginal discharge, fever, or flank pain.
Acute, uncomplicated cystitis is most common in women. Approximately one-third of all women have experienced at least one episode of cystitis by the age of 24 years, and nearly half will experience at least one episode during their lifetime. When a young woman presents to a health care provider with one or more symptoms, her probability of UTI is approximately 50%. Young women’s risk factors include sexual activity, use of spermicidal condoms or diaphragm, and genetic factors such as blood type or maternal history of recurrent cystitis. Healthy, noninstitutionalized older women can also experience recurrent cystitis. Risk factors among these women include changes in the perineal epithelium and vaginal microflora after menopause, incontinence, diabetes, and history of cystitis before menopause.
Although men can also suffer from cystitis, it is rare (annual incidence: <0.01% of men aged 21-50 years) in men with normal urinary anatomy who are younger than 35 years. Urethritis from sexually transmitted pathogens should always be considered in this age group, and prostatitis should always be ruled out in the older age group by a rectal examination. Any cystitis in a man is complicated, due to the presence of the prostate gland, and should be treated for 10-14 days to prevent a persistent prostatic infection.
Considering the frequency and morbidity of cystitis among young women, it is hardly surprising that the lay press and medical literature contain a host of ideas about how to prevent recurrent cystitis. These range from the suggestion that cotton underwear is “healthier” to wiping habits, voiding habits, and choice of beverage. Unfortunately, the vast majority of these preventive measures do not hold up to scientific study (Table 22-1).
| Factors With No Evidence of Effect on Cystitis | Factors With Evidence for Effect on Cystitis | |
|---|---|---|
| Promote | Prevent | |
| Precoital voiding | Spermicidea | Cranberry juice |
| Underwear fabric | Diaphragma | Prophylactic Antibiotics |
| Wiping pattern | Cervical capa | |
| Douching | Sexual activity | |
| Hot tub use | Genetic predisposition | |
| Delayed postcoital voidinga | ||
Recent studies have shown no effect of back-to-front wiping, precoital voiding, tampon use, underwear fabric choice, or use of noncotton hose or tights. Behaviors that do appear to have an impact on frequency of cystitis in young women include sexual activity (four or more episodes per month in one study), delayed postcoital voiding, use of spermicidal condoms (several studies), use of unlubricated condoms (one study), use of diaphragms or cervical caps, and intake of cranberry juice.
It can be concluded from Table 22-1 that there are few behaviorally oriented strategies that can be offered to young women who suffer from recurrent cystitis. Recommending a change in contraception to oral contraceptive pills, intrauterine devices, or nonspermicidal, lubricated condoms may be helpful.
Cranberry juice and cranberry extract have long been proposed as a possible way to prevent UTIs. Cranberries are thought to contain a substance that changes the surface properties of E coli and prevents it from adhering to the bladder wall. A recent Cochrane Review identified 10 studies comparing the effects of cranberry products with placebo, juice, or water. There was evidence to show cranberries in the form of juice or capsules could prevent recurrent UTIs in women. A reasonable dose in capsule form is 300-400 mg twice daily. As for juice, 8 oz three times daily of unsweetened juice is recommended. It is unclear how long the duration should be.
Prophylactic antibiotics, either low-dose daily antibiotics or postcoital antibiotics, remain the mainstay of prevention of recurrent UTIs for young women and can reduce recurrence rates up to 95%.
Risk factors for cystitis in older women include urologic factors such as incontinence, cystocele, and postvoid residual; hormonal factors resulting in a lack of protective lactobacillus colonization; and a prior history of cystitis. For the above-metioned risk factors, the most easily administered effective prevention is estrogen.
There are many possible ways to administer estrogen. These include traditional oral hormone replacement therapy, which is still considered indicative (after thorough discussion with the patient of risks and benefits) for menopausal symptoms; vaginal estrogen rings; or vaginal creams.
The only form of estrogen which has been proven to decrease recurrent UTIs in postmenopausal women is vaginal. The usual side effects of estrogen can be seen with vaginal use as well as oral. These include breast tenderness, vaginal bleeding, vaginal discharge, and vaginal irritation. Contraindications (as with oral estrogens) include a history of endometrial carcinoma, breast carcinoma, thromboembolic disorders, and liver disease. Consideration should be made of patients’ functional and cultural abilities before prescribing vaginal applications.
One study compared the effects of cranberry extract (500 mg daily) to trimethoprim for the prevention of recurrent UTIs in older women. There was only a slight advantage of the antibiotic over cranberry extract.
The only studies focusing on prevention of UTI in young men have investigated infant circumcision; because the risk of UTI is so low in normal men these studies are prohibitively expensive. The risk of UTI in normal boys hovers around 1% in the first 10 years of life, given that the number needed to treat (NNT) for circumcision is 111. In boys with recurrent UTI or high-grade ureteral reflux, the NNTs are 11 and 4, respectively. The complication rate of circumcision is 2%-10%, with adverse sequelae ranging from minor transient bleeding (common) to amputation of the penis (extremely rare).
Several investigators are currently evaluating the use of probiotics and vaccines for the prevention of UTI. Probiotics are benign living organisms, which in this case are used to boost the vaginal flora. They then defend against pathologic bacteria by competing for adhesion receptors and nutrients. Some species, such as Lactobacillus, even produce antimicrobial substances. Vaginal vaccines are working their way through clinical trials and are not yet commercially available; whether they will prove to be more efficacious than prophylactic antibiotics is yet to be determined. There are also studies looking at intentional colonization of the urothelium with Escherichia coli 83972. This looks promising, but needs more research.
Symptoms include dysuria, ideally felt more internally than externally, and of sudden onset; suprapubic pain; cloudy, smelly urine; frequency; and urgency.
Physical examination in the afebrile, otherwise healthy patient with a classic history is done essentially to rule out other diagnoses and to ensure that “red flags” are not present. The examination might range from checking a temperature and percussing the costovertebral angles to a full pelvic examination, depending on where the history leads. There are no pathognomonic signs on physical examination for cystitis.
Laboratory studies include dipstick test of urine, urinalysis, and urine culture. In some cases laboratory tests are not required to diagnose cystitis with high accuracy; however, they should probably only be omitted in settings where follow-up can be easily arranged in case of failure of treatment, which would of course indicate further workup. Figure 22-1 provides a diagnostic algorithm for cystitis.
Dipstick findings are positive for leukocyte esterase or nitrite, or both. Several references now support treatment of simple, uncomplicated UTI in the young, nonpregnant woman on the grounds of clinical history alone, if that history leads to high suspicion for cystitis (and low suspicion of STD). For women with an equivocal clinical history, urine dipstick analysis may be enough to reassign the women to high or low suspicion and treat or not treat accordingly.
Urinalysis will be positive for WBCs, with few or no epithelial cells. It should be noted, however, that urinalysis is more expensive than dipstick analysis and only minimally more accurate.
The gold standard of diagnosis is a culture growth of 100,000 (105) organisms in a midstream clean-catch sample. However, there are some patients who have classic clinical cases of UTI and only 100 (102) organisms on culture. Most laboratories are not equipped to detect anything fewer than 104 organisms. Culture is strongly suggested if a relapsing UTI or pyelonephritis is suspected to be sure of sensitivities and eradication (see Figure 22-1).
Figure 22-1.
Diagnostic algorithm for cystitis. STD, sexually transmitted disease; UTI, urinary tract infection. (Reproduced, with permission, from Bent S et al: Does this woman have an acute uncomplicated urinary tract infection? JAMA 2002; 287:2701.)
a In women who have risk factors for sexually transmitted diseases (STDs), consider testing for Chlamydia. The US Preventative Services Task Force recommends screening for Chlamydia for all women 25 years or younger and women of any age with more than one sex partner, a history of STD, or inconsistent use of condoms.
b For a definition of complicated UTI, see text.
c The only physical examination finding that increases the likelihood of UTI is costovertebral angle tenderness, and clinicians may consider not performing this test in patient with typical symptoms of acute uncomplicated UTI (as in telephone management).
Imaging studies generally are not required for patients with simple uncomplicated UTIs.
These tests are generally required only for failures of treatment, symptoms suggesting a diagnosis other than cystitis, or complicated cystitis (see section Complicated Cystitis, later).
See Table 22-2.
| If Patient Has | Consider |
|---|---|
| Fever | Urosepsis, pyelonephritis, pelvic inflammatory disease (PID) |
| Vaginal discharge | Sexually transmitted disease (STD), PID |
| External burning pain | Vulvovaginitis, especially candidal vaginitis |
| Costovertebral angle tenderness | Pyelonephritis |
| Nausea/vomiting | Pyelonephritis, urosepsis, inability to tolerate oral medications |
| Recent UTI (<2 wk) | Incompletely treated, resistant pathogen; urologic abnormality, including stones and unusual anatomy; interstitial cystitis |
| Dyspareunia | STD, PID, psychogenic causes |
| Recent trauma or instrumentation | Complicated UTI |
| Pregnancy | Antibiotic choice, treatment duration |
| Severe, colicky flank pain | UTI complicated by stones; preexisting or struvite stone caused by urea-splitting bacteria |
| Joint pains, sterile urine | Spondyloarthropathy, eg, Reiter or Behçet syndrome |
| History of childhood infections, urologic surgery | Abnormal anatomy |
| History of kidney stones | Complicated UTI; bacterial persistence in stones |
| Diabetes | Complicated UTI |
| Immunosuppression | Complicated UTI |
There are virtually no complications from repeated uncomplicated cystitis if it is recognized and treated. Delay in treatment may lead to ascending infection and pyelonephritis, but this has not been confirmed. In the case of infection with urea-splitting bacteria, “infection stones” of struvite with bacteria trapped in the interstices may be formed. These stones lead to persistent bacteriuria and must be completely removed to clear the infection. Proteus mirabilis, S saprophyticus, and Klebsiella bacteria can all split urea and lead to stones.
