Urinary Tract Infection

Contributor: Francis Nuthalapaty, MD
Last Update: 04/05/2018     

The female urinary tract undergoes profound changes during pregnancy. These changes predispose to the development of urinary tract infections which are the most common bacterial infections encountered during pregnancy. Universal screening for asymptomatic bacteriuria and additional risk factor base screening can reduce the morbidity related to urinary tract infections during pregnancy.

Universal Screening for Asymptomatic Bacteriuria
Asymptomatic bacteriuria (ASB) is defined as a positive urine culture in a patient without symptoms of urinary tract infection. The condition is present in 2-10% of gravidas at the first antenatal visit. Pregnancy does not predispose to the acquisition of ASB as only 1% of initially screen negative gravidas develop ASB during pregnancy. Asymptomatic bacteriuria in healthy nongravid women poses little or no significant health risk. During pregnancy however, 30% of gravid women with untreated ASB develop symptomatic urinary tract infection.

Many of these acute infections can be classified as pyelonephritis on the basis of fever, costovertebral tenderness, and pyuria. Conversely, only 0.2-2.0% of gravidas who are screened early in gestation and found not to have bacteriuria will subsequently developed symptomatic urinary tract infection during pregnancy. Pyelonephritis can be life-threatening during pregnancy; both adult respiratory distress syndrome and septic shock can occur. Asymptomatic bacteriuria is also associated with an increased risk of preterm delivery and low birth weight.

Screening Approach
All pregnant women should be screened for ASB at their first antenatal visit. Each patient should submit a midstream clean voided urine specimen. The specimen should be sent for urine culture and sensitivities.
A positive culture is defined as:

• Clean–void: 1 bacterial species in quantitative counts >100,000 cfu/mL
• Catheter: 1 bacterial species in quantitative counts >100 cfu/mL

Isolation of more than one species or the presence of Lactobacillus or Propionibacterium may indicate a contaminated specimen. If contamination is suspected, obtain a second urine specimen by mini-cath. Cultures with a single organism colony count <100,000 cfu/mL should be repeated. If a persistent single organism colony count <100,000 cfu/mL is noted, then treat as described below.

Treatment
Short course antibiotic therapy is usually effective in eradicating asymptomatic bacteriuria in pregnancy. Currently the evidence regarding an association between nitrofuran and sulfonamide classes of antibiotics and birth defects is mixed. To exercise an abundance of caution, neither nitrofurantoin nor trimethoprim–sulfamethoxazole should be used for treating urinary tract infections in the first trimester of pregnancy unless no other antibiotic is likely to be effective. In addition, trimethoprim-sulfamethoxazole should be avoided just prior to expected delivery because it can displace bilirubin from protein–binding sites in the newborn increasing the risk of neonatal jaundice. Sulfamethoxazole/trimethoprim is rarely indicated for treatment of uncomplicated UTI, since approximately 25% of the E. Coli isolates tested by the microbiology lab at Greenville Memorial Hospital are resistant to sulfamethoxazole/trimethoprim.

• First line (except in the first trimester): Nitrofurantoin 100 mg po BID (Macrobid) x 5 days
• Second line: Cephalexin 500 mg po BID (Keflex) x 7 days

For patients with GBS identified in the urine (>10,000 cfu/mL), treatment should be tailored to sensitivities ( PCN, amoxicillin or cephalosporin). No test of cure is required.

Follow-up
Approximately one third of women with ASB will experience a recurrent infection during pregnancy. Therefore, follow-up is recommended:

• Repeat clean-void urine C&S 7-14 days after initial treatment is completed. If again positive, check patient compliance and bacterial sensitivities.
• If urine culture is negative after treatment, then repeat clean–void urine C&S each trimester.

Women with a repeat positive culture should be treated for 7-10 days with an effective antibiotic as per sensitivities. Women with 2 or more positive urine cultures should be treated with chronic antibiotic suppression using Nitrofurantoin 100 mg QHS.

Additional Risk Factor Based Screening
Certain medical comorbidities predispose to a significantly increased risk of urinary tract infections. Women with the following conditions should be screened with urine cultures each trimester:

• Heterozygous or homozygous sickle cell states
• Insulin-dependent pre-gestational diabetes
• HIV disease or other immunocompromised conditions
• Urinary tract anomalies
• Neurogenic bladder
• Nephrolithiasis

Acute Cystitis 
Diagnosis
Initial diagnosis is made by history and urinalysis of clean-catch urine (presence of WBCs and bacteria). A urine C&S confirms a diagnosis. E.coli is isolated from 75-80% of positive urine cultures.

Treatment
Pregnant women with symptomatic UTI should be treated with a course of oral antibiotics as long as they do not have symptoms suggestive of pyelonephritis. See above justification for antibiotic choice.

• First line (except in the first trimester): Nitrofurantoin 100 mg po BID (Macrobid) x 5 days
• Second line: Cephalexin 500 mg po BID (Keflex) x 7 days

Follow-up
Reculture (midstream clean-void) 7-14 days after treatment. Women with a recurrent UTI should be treated for 7-10 days with an effective antibiotic as per sensitivities. Women with 2 episodes of cystitis should be treated with suppressive therapy using Nitrofurantoin 100 mg po QHS.

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References

1. Sulfonamides, nitrofurantoin, and risk of birth defects. Committee Opinion No. 717. American College of Obstetricians and Gynecologists. Obstet Gynecol 2017; 130:e150-2.
2. Nordeng H, Lupattelli A, Romoren M, Koren G. Neonatal outcomes after gestational exposure to nitrofurantoin. Obstet Gynecol 2013;121:306-13.
3. Fihn SD. Acute uncomplicated urinary tract infection in women. N Engl J Med 2003;349:259-64.
4. Mabie WC, Barton JR, Sibai B. Septic shock in pregnancy. Obstet Gynecol 1997;90:553-60.
5. Raz R, Sakran W, Chazan B et al. Long-term follow-up of women hospitalized for acute pyelonephritis. Clin Infect Dis 2003;37:1014-17.
6. Lumbiganon P, Laopaiboon M, Thinkhamrop J. Screening and treating asymptomatic bacteriuria in pregnancy. Curr Opin Obstet Gynecol 2010;22:95-99.