Clinical Review

UTI in pregnancy: 6 questions to guide therapy

OBG Manag. 2004 November;16(11):36-54

Crucial are treatment, test of cure, frequent screening until delivery, and antibiotic suppression, when indicated.

References

1. Gilstrap LC, III, Ramin SM. Urinary tract infections during pregnancy. Obstet Gynecol Clin North Am. 2001;28:581-591.

2. Hooton TM, Scholes D, Hughes JP, et al. A prospective study of risk factors for symptomatic urinary tract infection in young women. N Engl J Med. 1996;335:468-474.

3. American College of Obstetricians and Gynecologists. Antimicrobial therapy for obstetric patients. ACOG Technical Bulletin No. 245. Washington, DC: ACOG; 1998.

4. McMahon MJ, Ananth CV, Liston RM. Gestational diabetes mellitus. Risk factors, obstetric complications and infant outcomes. J Reprod Med. 1998;43:372-378.

5. Pastore LM, Savitz DA, Thorp JM, Jr. Predictors of urinary tract infection at the first prenatal visit. Epidemiology. 1999;10:282-287.

6. Stamm WE, Counts GW, Running KR, Fihn S, Turck M, Holmes KK. Diagnosis of coliform infection in acutely dysuric women. N Engl J Med. 1982;307:463-468.

7. Bachman JW, Heise RH, Naessens JM, Timmerman MG. A study of various tests to detect asymptomatic urinary tract infections in an obstetric population. JAMA. 1993;270:1971-1974.

8. Harris RE, Gilstrap LC, III. Cystitis during pregnancy: a distinct clinical entity. Obstet Gynecol. 1981;57:578-580.

9. Gilstrap LC, III, Cunningham FG, Whalley PJ. Acute pyelonephritis in pregnancy: an anterospective study. Obstet Gynecol. 1981;57:409-413.

10. Whalley P. Bacteriuria of pregnancy. Am J Obstet Gynecol. 1967;97:723-738.

11. Cunningham FG, Lucas MJ. Urinary tract infections complicating pregnancy. Baillieres Clin Obstet Gynaecol. 1994;8:353-373.

12. Cox SM, Shelburne P, Mason R, Guss S, Cunningham FG. Mechanisms of hemolysis and anemia associated with acute antepartum pyelonephritis. Am J Obstet Gynecol. 1991;164:587-590.

13. Cunningham FG, Lucas MJ, Hankins GD. Pulmonary injury complicating antepartum pyelonephritis. Am J Obstet Gynecol. 1987;156:797-807.

14. Whalley PJ, Cunningham FG, Martin FG. Transient renal dysfunction associated with acute pyelonephritis of pregnancy. Obstet Gynecol. 1975;46:174-177.

15. Romero R, Oyarzun E, Mazor M, Sirtori M, Hobbins JC, Bracken M. Meta-analysis of the relationship between asymptomatic bacteriuria and preterm delivery/low birth weight. Obstet Gynecol. 1989;73:576-582.

16. Schieve LA, Handler A, Hershow R, Persky V, Davis F. Urinary tract infection during pregnancy: its association with maternal morbidity and perinatal outcome. Am J Public Health. 1994;84:405-410.

17. Mittendorf R, Williams MA, Kass EH. Prevention of preterm delivery and low birth weight associated with asymptomatic bacteriuria. Clin Infect Dis. 1992;14:927-932.

18. Gilstrap LC, Leveno KJ, Cunningham FG, Whalley PJ, Roark ML. Renal infection and pregnancy outcome. Am J Obstet Gynecol. 1981;141:709-716.

19. Millar LK, DeBuque L, Wing DA. Uterine contraction frequency during treatment of pyelonephritis in pregnancy and subsequent risk of preterm birth. J Perinatal Med. 2003;31(1):41-46.

20. Kaul AK, Khan S, Martens MG, Crosson JT, Lupo VR, Kaul R. Experimental gestational pyelonephritis induces preterm births and low birth weights in C3H/HeJ mice. Infect Immun. 1999;67:5958-5966.

21. Vazquez JC, Villar J. Treatments for symptomatic urinary tract infections during pregnancy. Cochrane Database Syst Rev. 2003(4);CD002256.-

22. Smaill F. Antibiotics for asymptomatic bacteriuria in pregnancy. Cochrane Database Syst Rev. 2001(2);CD000490.-

23. Fihn SD. Clinical practice. Acute uncomplicated urinary tract infection in women. N Engl J Med. 2003;349:259-266.

24. Ovalle A, Levancini M. Urinary tract infections in pregnancy. Curr Opin Urol. 2001;11:55-59.

25. Villar J, Lydon-Rochelle MT, Gulmezoglu AM, Roganti A. Duration of treatment for asymptomatic bacteriuria during pregnancy. Cochrane Database Syst Rev. 2000(2);CD000491.-

26. Millar LK, Wing DA, Paul RH, Grimes DA. Outpatient treatment of pyelonephritis in pregnancy: a randomized controlled trial. Obstet Gynecol. 1995;86:560-564.

27. Wing DA, Hendershott CM, DeBuque L, Millar LK. Outpatient treatment of acute pyelonephritis in pregnancy after 24 weeks. Obstet Gynecol. 1999;94:683-688.

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Fast Track

Screen all pregnant women early; screen those with risk factors often.

A threshold of 100 CFL/mL raises the sensitivity of a urine culture in symptomatic patients.

When a rapid test is positive but the patient has no symptoms, treat only if urine culture is positive.

Make sure the urine culture is negative after either single-dose or other antibiotic treatment.

Change antibiotics based on urine culture sensitivity profiles.

THE CASE: SIGNS AND SYMPTOMS

A 29–year–old nullipara at 18 weeks’ gestation complains of fevers and back pain. She had a diagnosis of urinary tract infection with sulfonamide-resistant Escherichia coli at 9 weeks of gestation, which was treated with nitrofurantoin, 100 mg by mouth twice a day for 7 days. A test of cure by urine culture was negative.

Now her temperature is 101°F and she has right costovertebral angle tenderness.

How should you proceed?

Anatomy is destiny, in the case of susceptibility to urinary tract infection (UTI). The female urethra is only 3 cm to 4 cm long, and its proximity to the vagina, anus, and rectum facilitates colonization of normal gastrointestinal flora in the bladder.¹

Sexual activity also facilitates migration of normal gastrointestinal flora to the female urethra.²

Anatomical features of pregnancy exacerbate the female predisposition to urinary tract infection. In pregnancy, hormonal and mechanical changes that occur in the urinary tract lead to urinary stasis and ureterovesical reflux—setting the stage for urinary tract infection (FIGURE 1).

Who should be screened?

All pregnant women should be screened for UTI early in pregnancy, according to the American College of Obstetricians and Gynecologists.³

I recommend a urine culture screening for all pregnant women at their first prenatal visit.

Screen often if she has risk factors

I recommend frequent screening (at least every trimester) by urine culture, in pregnant women with any of these risk factors:

diabetes mellitus, including gestational diabetes⁴;
urologic abnormalities—specifically, neurogenic bladder;
prepregnancy (for example, 2 to 3 infections per year) and antepartum history of UTI prior to initiation of prenatal care⁵;
sickle cell hemoglobinopathy.⁵

Which test is best?

The gold standard for detecting bacteria in urine is by culture.

Which threshold to use?

The standard definition of a positive urine culture from a clean-catch, midstream, voided specimen is ≥100,000 colony forming units (CFU) per mL of a single organism. However, in symptomatic patients, the test’s sensitivity is increased by lowering the cut-off to 100 CFU/mL of a single organism.⁶ In women with urinary symptoms, only 50% of patients had 100,000 CFU/mL by urine culture collected from clean-catch, midstream, voided specimens, though all of them had positive cultures from suprapubic taps.

The clean-catch, midstream, voided specimen is the specimen of choice for practical purposes, since it is noninvasive and easily obtained in the office setting.

For the record: The presence of any organism represents UTI in specimens obtained via suprapubic aspiration of the bladder; 100 CFU/mL of a single organism is positive for specimens obtained by urethral catheterization.

I recommend that, when obtaining urine cultures via clean-catch, midstream, voided specimens:

for asymptomatic patients, use ≥100,000 CFU/mL of a single organism.
in symptomatic patients, use ≥100 CFU/mL of a single organism.

What about rapid tests?

Urinary sediment analysis and urine dipstick testing offer speed and low cost, but with lower accuracy than urine cultures, which require 24 to 48 hours for results and cost more.

Urinary sediment analysis can diagnose pyuria, defined as a clean-catch, midstream, voided specimen, which is spun and which has >10 leukocytes per high-power field.

Pyuria can occur without infection due to:

previous treatment with antibiotics,
contamination of urine sample by sterilizing solution,
contamination of urine sample with vaginal leukocytes,
chronic interstitial nephritis (such as analgesic abuse),
uroepithelial tumor, and
nephrolithiasis.

Pyuria on urinalysis has low sensitivity (25%) but high specificity (99%).

Bacteria visualized on microscopic examination is more sensitive (75%) but less specific (60%).⁷

Urinary dipstick testing—fast, convenient, and low in cost—is considered positive if it identifies either leukocyte esterase or nitrite. Positive leukocyte esterase signifies pyuria. Positive nitrite indicates the presence of enteric organisms that convert urinary nitrate to nitrite.

With either finding, dipstick sensitivity is only 50%, although specificity is 97%.⁷

I recommend:

If a symptomatic patient’s rapid test is positive, obtain a urine culture, empirically treat for UTI, and then use urine culture results to decide whether to continue treatment.
If an asymptomatic patient’s rapid test is positive, obtain a urine culture and treat only if the culture is positive.

What urinary tract disorders occur in pregnancy?

First, determine if the patient has urinary tract symptoms and, if so, whether the symptoms are typical of upper or lower urinary tract infections.