Clinical Practice Guidelines Antenatal care - Module I

8.7 Asymptomatic bacteriuria

Page last updated: 02 April 2013

Screening for asymptomatic bacteriuria in pregnancy allows treatment to be offered to reduce the risk of progression to pyelonephritis.

8.7.1 Background

Asymptomatic bacteriuria is the persistent bacterial colonisation of the urinary tract (usually by Escherichia coli) without symptoms. It is common in pregnancy. Asymptomatic bacteriuria in Australia
  • Incidence — Incidence of asymptomatic bacteriuria during pregnancy has been reported to be 2–10% in the United States (Andrews & Gilstrap 1992; Sweet 1977) and 2–5% in the United Kingdom (Little 1966; Campbell-Brown et al 1987; Foley et al 1987). In Australia, available estimates suggest that asymptomatic bacteriuria during pregnancy may be more common among Aboriginal and Torres Strait Islander women (Hunt 2004; Bookallil et al 2005; Panaretto et al 2006).
  • Risk factors — The prevalence of infection is most closely related to socioeconomic status and is similar in pregnant and non-pregnant women (Turck et al 1962; Whalley 1967). Other factors associated with an increased risk of bacteriuria include a history of recurrent urinary tract infections, diabetes and anatomical abnormalities of the urinary tract (Golan et al 1989).
Risks associated with asymptomatic bacteriuria in pregnancy

While asymptomatic bacteriuria in non-pregnant women is usually benign, in pregnancy it increases the likelihood of kidney involvement (pyelonephritis), with an incidence of around 30% in affected women (Whalley 1967).

An association between untreated asymptomatic bacteriuria and low birth weight and preterm birth has also been suggested (LeBlanc & McGanity 1964; Kincaid-Smith & Bullen 1965; Little 1966; Savage et al 1967). However, while a reduction in preterm birth and low birth weight is consistent with understanding of the role of infection in pregnancy complications (Smaill 2007; Smaill & Vasquez 2007), other factors may be involved (eg other asymptomatic genitourinary infections) (Campbell-Brown et al 1987; Maclean 2001) or links with socioeconomic status (Romero et al 1989). There may only be an association between asymptomatic bacteriuria and preterm birth if the infection progresses to pyelonephritis (Meis et al 1995).

8.7.2 Screening for asymptomatic bacteriuria

Summary of the evidence

Universal screening for asymptomatic bacteriuria in pregnancy is recommended in the United Kingdom (NICE 2008), the United States (USPSTF 2004; Nicolle et al 2005), Canada (Nicolle 1994) and Scotland (SIGN 2006), based on the effectiveness of available treatments and the reduced risk of pyelonephritis.

Benefits of screening

Screening for asymptomatic bacteriuria has been shown to reduce the number of women per 1,000 who experience pyelonephritis from 23.2 with no screening, to 16.2 with dipstick testing and 11.2 with urine culture (Rouse et al 1995). Both tests were found to be cost beneficial compared to no screening.

Effectiveness of interventions to treat asymptomatic bacteriuria

A Cochrane review found that antibiotic treatment compared with placebo or no treatment is effective in clearing asymptomatic bacteriuria (RR 0.25; 95% CI 0.14–0.48). The incidence of pyelonephritis was
reduced by 75% (RR 0.23; 95% CI 0.13–0.41) (Smaill & Vasquez 2007).

Recommendation - Grade A

18. Routinely offer and recommend testing for asymptomatic bacteriuria early in pregnancy as treatment is effective and reduces the risk of pyelonephritis.
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Testing method

Midstream urine culture is considered the standard for diagnosis of asymptomatic bacteriuria in pregnancy (NICE 2008).

Dipstick urinalysis of nitrites may be useful for excluding asymptomatic bacteriuria but is not accurate for diagnosis (Deville et al 2004). A meta-analysis (Deville et al 2004) and a small number of RCTs (Teppa & Roberts 2005; Karabulut 2007; Eigbefoh et al 2008; Mignini et al 2009) have shown high specificity (89–100%) but low sensitivity (33–98%), with a mid range around 50%. Lower level studies have had similar results.

Recommendation - Grade A

19. Use urine culture testing wherever possible, as it is the most accurate means of detecting asymptomatic bacteriuria.

Timing of the test

There is no consensus in the literature about the optimal timing and screening frequency for asymptomatic bacteriuria. However, in a prospective study (n=3,254), a single urine specimen obtained between 12 and 16 weeks gestation identified 80% of women who ultimately had asymptomatic bacteriuria (Stenqvist et al 1989).

Testing in rural and remote areas

Due to difficulties in transporting specimens to laboratories, dipstick tests are commonly used in remote areas to ‘rule out’ asymptomatic bacteriuria, with samples from women testing positive then sent for culture to confirm infection. While urine culture is the preferred method of testing, this process has been found to be cost effective (Rouse et al 1995). However, factors specific to conditions in rural and remote Australia (eg high humidity and ambient temperatures) may contribute to under diagnosis and overtreatment. Considerations in testing for asymptomatic bacteriuria in these areas include (Bookallil et al 2005):
  • whether specimens can be provided to pathology services within the timeframe in which they can still be cultured (ideally within 24 hours);
  • the availability of appropriate storage facilities for dipstick tests;
  • the consequences of treating all women with a positive dipstick result given the high rate of false positives and the risk of increased resistance to antibiotics associated with over-prescribing; and
  • and recall systems for women with a positive result on culture.

Practice point

s. Where access to pathology services is limited, dipstick tests may be used to exclude infection, with positive results confirmed by urine culture. Appropriate storage of dipsticks is essential to the accuracy of these tests.

Considerations beyond the first trimester

Although most guidelines recommend a single urine culture at the first antenatal visit, two prospective studies have concluded that urine should be cultured in each trimester of pregnancy to improve the detection rate of asymptomatic bacteriuria (McIsaac et al 2005; Tugrul et al 2005). There has been no prospective evaluation of repeated testing during pregnancy (Schnarr & Smaill 2008).

8.7.3 Practice summary — screening for asymptomatic bacteriuria

When — Early in antenatal care
Who — Midwife; GP; obstetrician; Aboriginal and Torres Strait Islander health worker; multicultural health worker
  • Discuss screening for asymptomatic bacteriuria — Explain that identifying urinary tract infection enables women to be treated with antibiotics and avoids the risk of complications.
  • Document and follow-up — Note the results of screening in the woman’s record and have a follow-up system in place so that appropriate treatment is provided if a woman is found to have bacteriuria.

8.7.4 Resources

Villar J, Widmer M, Lydon-Rochelle M et al (2000) Duration of treatment for asymptomatic bacteriuria during pregnancy. Cochrane Database of Systematic Reviews 2000, Issue 2. Art. No.: CD000491. DOI: 10.1002/14651858. CD000491.
For more information please visit The Cochrane Collaboration website.
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8.7.5 References

Andrews WW & Gilstrap LC (1992) Urinary tract infections. In: Gleicher N editor(s). Principles and Practice of Medical Therapies in Pregnancy. Appleton and Lange, pp913–7.

Bookallil M, Chalmers E, Bell A (2005) Challenges in preventing pyelonephritis in pregnant women in Indigenous communities. Rural Remote Health 5: 395 (online).

Campbell-Brown M, McFadyen IR, Seal DV et al (1987) Is screening for bacteriuria in pregnancy worth while? Brit Med J 294: 1579–82.

Deville WL, Yzermans JC, van Duijn NP et al (2004) The urine dipstick test useful to rule out infections: a meta-analysis of the accuracy. BMC Urology 4: 4.

Eigbefoh JO, Isabu P, Okpere E et al (2008) The diagnostic accuracy of the rapid dipstick test to predict asymptomatic urinary tract infection of pregnancy. J Obstet Gynaecol 28(5): 490–95.

Foley ME, Farquharson R, Stronge JM (1987) Is screening for bacteriuria in pregnancy worthwhile? Brit Med J 295: 270.

Golan A, Wexler S, Amit A et al (1989) Asymptomatic bacteriuria in normal and high-risk pregnancy. Eur J Obstet Gynecol Reprod Biol 33: 101–8.

Hunt J (2004) Pregnancy Care and Problems for Women Giving Birth at Royal Darwin Hospital. Carlton: Centre for the Study of Mothers’ and Children’s Health.

Karabulut A (2007) Asymptomatic bacteriuria in pregnancy: Can automated urinalysis be helpful for detection?” J Turkish German Gynecol Assoc Artemis 8(4): 367–71.

Kincaid-Smith P & Bullen M (1965) Bacteriuria in pregnancy. Lancet 1(7382): 395–99.

LeBlanc AL & McGanity WJ (1964) The impact of bacteriuria in pregnancy: a survey of 1300 pregnant patients. Biologie Medicale 22: 336–47.

Little PJ (1966) The incidence of urinary infection in 5000 pregnant women. Lancet 2(7470): 925–28.

MacLean AB (2001) Urinary tract infection in pregnancy. Int J Antimicrob Agents 17: 273–76.

McIsaac W, Carroll JC, Biringer A et al (2005) Screening for asymptomatic bacteriuria in pregnancy. J Obstet Gynaecol Can 27: 20–24.

Meis PJ, Michielutte R, Peters TJ et al (1995) Factors associated with preterm birth in Cardiff, Wales. II. Indicated and spontaneous preterm birth. Am J Obstet Gynecol 173: 597–602.

Mignini L, Carroli G, Abalos E et al (2009) Accuracy of diagnostic tests to detect asymptomatic bacteriuria during pregnancy. Obstet Gynecol 113 (2 Part 1): 346–52.

NICE (2008) Antenatal Care. Routine Care for the Healthy Pregnant Woman. National Collaborating Centre for Women’s and Children’s Health. Commissioned by the National Institute for Health and Clinical Excellence. London: RCOG Press.

Nicolle LE (1994) Screening for asymptomatic bacteriuria in pregnancy. In: Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada, pp100–106.

Nicolle LE, Bradley S, Colgan R et al (2005) Infectious diseases society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis 40: 643–54.

Panaretto KS, Lee HM, Mitchell MR et al (2006) Prevalence of sexually transmitted infections in pregnant urban Aboriginal and Torres Strait Islander women in northern Australia. Aust NZ J Obstet Gynaecol 46(3) 217–24.

Romero R, Oyarzun E, Mazor M et al (1989) Meta-analysis of the relationship between asymptomatic bacteriuria and preterm delivery/low birth weight. Obstet Gynecol 73: 576–82.

Rouse DJ, Andrews WW, Goldenberg RL et al (1995) Screening and treatment of asymptomatic bacteriuria of pregnancy to prevent pyelonephritis: a cost-effectiveness and cost-beneficial analysis. Obstet Gynecol 86: 119–23.
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Savage WE, Hajj SN, Kass EH (1967) Demographic and prognostic characteristics of bacteriuria in pregnancy. Medicine 46: 385–407.

Schnarr J & Smaill F (2008) Asymptomatic bacteriuria and symptomatic urinary tract infections in pregnancy. Eur J Clin Invest 38(S2): 50–57.

SIGN (2006) Management of Suspected Bacterial Urinary Tract Infection in Adults. A National Clinical Guideline. Edinburgh: Scottish Intercollegiate Guidelines Network.

Smaill F (2007) Asymptomatic bacteriuria in pregnancy. Best Pract Res Clin Obstet Gynaecol 21(3): 439–50.

Smaill FM & Vazquez JC (2007) Antibiotics for asymptomatic bacteriuria in pregnancy. Cochrane Database of Systematic Reviews 2007, Issue 2. Art. No.: CD000490. DOI: 10.1002/14651858.CD000490.pub2.

Stenqvist K, Dahlen-Nilsson I, Lidin-Janson G et al (1989) Bacteriuria in pregnancy. Frequency and risk of acquisition. Am J Epidemiol 129: 372–79.

Sweet RL (1977) Bacteriuria and pyelonephritis during pregnancy. Sem Perinatol 1: 25–40.

Teppa RJ & Roberts JM (2005) The Uriscreen test to detect significant asymptomatic bacteriuria during pregnancy. J Soc Gynecol Invest 12(1): 50–53.

Tugrul S, Oral O, Kumru P et al (2005) Evaluation and importance of asymptomatic bacteriuria in pregnancy. Clin Exp Obstet Gynecol 32: 237–40.

Turck M, Goff BS, Petersdorf RG (1962) Bacteriuria in pregnancy; relationship to socioeconomic factors. New Engl J Med 266: 857–60.

USPSTF (2004) Screening for Asymptomatic Bacteriuria: Recommendation Statement. Rockville (MD): Agency for Healthcare Research and Quality.

Whalley P (1967) Bacteriuria of pregnancy. Am J Obstet Gynecol 97: 723–38.