Approximately 25% of women with acute cystitis develop recurrent urinary tract infections (UTIs). (See Urinary Tract Infections in Females.) The number of recurrences experienced varies for each woman (range, 0.3-7.6 episodes per year), and recurrences often cluster in time. Most recurrent infections are from bacteria colonizing the fecal or periurethral reservoirs. 
Women who develop a UTI within 2 weeks of a treated UTI either have a new infection or have a recurrence of the infection caused by the original uropathogen. The latter is supported by cultures that grow the same species, especially if it is biotyped or shares the same antimicrobial sensitivities. Looking for a source of persistent infection, such as a structural abnormality (eg, calculus, abscess, cystic disease), is prudent.
Prevention of UTIs has become even more important because of the recognition of what has been described a "stealth pandemic" of Escherichia coli sequence type 131 (ST131) that is resistant to both fluoroquinolones and extended spectrum beta-lactamases. Across the board, E coli is responsible for at least 80% of the 7 million uncomplicated outpatient UTIs that occur yearly in the United States. E coli ST131, is becoming more frequently isolated from clinical cases. 
The 3 main risk factors for recurrent urinary tract infection (UTI) in women are an increased frequency of sexual intercourse, the use of a spermicide and diaphragm, and the loss of estrogen’s effect in the vagina and periurethral structures. The last 2 situations lead to eradication of the vaginal lactobacilli. Patients using a spermicide should consider alternative methods of contraception.
Women with 2 or 3 recurrent UTIs yearly may benefit from behavioral modification. Behavioral modifications are generally easy, low-risk, and low-cost maneuvers.
Sexually active women may attempt voiding immediately after intercourse to lessen the risk of coitus-related introduction of bacteria into the bladder. Some authors recommend large urinary flow volumes as a measure that will reduce the risk of UTI.
Drinking cranberry juice (10 oz/day) or taking cranberry tablets may offer some benefit in reducing recurrent UTI and does not appear to be harmful. The positive effect appears mainly to women with recurrent UTIs 
One study found lower rates of UTI recurrence in women who drank 50 mL of cranberry-lingonberry concentrate daily for 6 months.  The mechanism of action of cranberry juice has not been fully clarified.  The juice is bacteriostatic perhaps due to hippuric acid. Another mechanism may involve suppression of Escherichia coli fimbriae by proanthocyanidins (tannins). This theoretically should be under the attachment of urinary pathogens to the bladder mucosal cells. The studies conducted have generally been flawed because of small numbers, unknown amounts of active ingredients, and a high rate of nonadherence to drinking adequate amounts of cranberry juice.  Ascorbic acid (vitamin C) has no preventative growth because it does not cause significant urinary acidification.
Self-Initiated Antibiotic Therapy
Self-initiated antibiotic therapy may be an acceptable alternative for women with recurrent UTIs. The clinician should educate the patient about the warning signs of a persistent or worsening infection despite therapy.
In one study, women with a history of at least 2 urinary tract infections (UTIs) in the past year proved capable of self-diagnosing and treating UTIs.  Uropathogens were isolated in 84% of 172 UTIs and sterile pyuria in 11%; clinical and microbiologic cures were achieved in about 95% of episodes. Self-treatment consisted of ofloxacin tablets, 200-mg tablets taken twice daily for 3 days if UTI symptoms developed, or levofloxacin, 250-mg tablets taken once daily for 3 days.
A study from China evaluated patient-initiated single-dose antibiotic prophylaxis and continuous long-term low-dose daily antibiotic use for the prevention of recurrent UTI in 68 postmenopausal women, finding that the former was as effective as the latter and was associated with fewer gastrointestinal adverse events. 
Women with more than 3 recurrent UTIs yearly should be considered for more aggressive prophylactic regimens in addition to behavioral modification. Women whose recurrent UTIs are associated with sexual intercourse should be offered postcoital prophylaxis. This involves taking a single dose of an effective antimicrobial (eg, nitrofurantoin 50 mg, trimethoprim-sulfamethoxazole [TMP-SMX] 40/200 mg, or cephalexin 500 mg) after sexual intercourse.
A double-blind, double-dummy noninferiority trial found that TMP-SMX (480 mg once daily) is more effective than cranberry capsules (500 mg twice daily) in preventing recurrent UTIs. However, after 1 month, patients in the TMP-SMX group showed increased resistance to the antibiotic as well as to trimethoprim, amoxicillin, and ciprofloxacin. This resistance reached baseline levels 3 months after discontinuance. 
Continuous antimicrobial prophylaxis may be required for women in whom a postcoital regimen fails; women who do not associate frequent UTIs with a modifiable cause; or those who are at risk for recurrent complicated UTIs. Regimens include the following:
TMP-SMX - 40/200 mg at bedtime or 3 times weekly
Nitrofurantoin - 50-100 mg at bedtime or 3 times weekly
Norfloxacin - 200 mg at bedtime or 3 times weekly
Trimethoprim - 100 mg at bedtime or 3 times weekly
These regimens have been shown to be safe and effective, even after 5 years of use. However, after 6-12 months, a trial without the medication is warranted, because as many as 30% of women experience a prolonged UTI-free period. Prophylaxis may be reinstituted if the patient again develops recurrent UTIs.
Postmenopausal women who have recurrent UTIs may benefit from estrogen replacement, either systemic or local. A randomized, double-blind, placebo-controlled trial in 93 postmenopausal women found that estriol in a vaginal cream (0.5 mg nightly for 2 weeks, then twice weekly for 8 months) significantly reduced the incidence of recurrent UTI.  The effect probably is related to the restoration of lactobacilli, which replace Enterobacteriaceae and decrease the vaginal pH.
Prevention in Specific Populations
Patients with spinal cord injury
For patients with spinal cord injury, the efficacy of prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMX) or nitrofurantoin has been demonstrated. The possibility of developing resistant organisms is a concern, especially in an institutional setting. One option includes the use of methenamine (1 g 3 times daily), alternating every 2 months with nitrofurantoin (50-100 mg twice daily). Methenamine is converted into formic acid, which is bactericidal.
Risk can also be decreased by the use of intermittent catheterization. (See Urinary Tract Infections in Spinal Cord Injury Patients and Urethral Catheterization in Women.)
Many steps can be taken to prevent catheter-associated urinary tract infections (UTIs).  These steps can postpone the development of a UTI for weeks but are not likely to be successful in chronically catheterized patients. One to three days of antibiotic prophylaxis at the time of catheter removal results in a decrease a symptomatic UTIs. This should probably be considered in patients who are severely immunosuppressed, not as a general practice, which may result in a significant increase in the use of antibiotics in hospitalized patients.  (See Catheter-Related Urinary Tract Infections and Urethral Catheterization in Women.)
Renal transplant recipients
UTI is an important complication after renal transplantation, especially in the initial months after the procedure, and can result in graft failure and patient mortality. Prophylaxis with TMP-SMX (1 tablet/day orally), beginning 2-4 days after surgery and continuing for 4-8 months, can reduce the incidence of UTIs (especially after catheter removal), febrile hospital days, bacterial infections (during and after hospitalization), and graft rejection.