Antibiotics for asymptomatic bacteriuria in pregnancy
Antibiotics are effective for the treatment of asymptomatic bacteriuria in pregnancy, decreasing the incidence of pyelonephritis in the treated women. Antibiotic therapy also appears to reduce the incidence of low-birth-weight and preterm babies.
RHL Commentary by Tolosa JE
1. EVIDENCE SUMMARY
The Cochrane review was revised and updated in 2007. The conclusions have not changed but the review text was extensively revised and one more trial identified (1). Overall, fourteen trials were included. Antibiotic treatment was effective in clearing bacteriuria (relative risk [RR] 0.25; 95% confidence interval [CI] 0.14 to 0.48) and reducing the risk of pyelonephritis (RR: 0.23; 95% CI: 0.13 to 0.41). The reviewers separated the outcomes low birthweight and preterm birth which had been grouped together in the earlier version. Antibiotic treatment reduced the risk of low birthweight (RR: 0.66 95% CI: 0.49 to 0.89) but not preterm birth.
The effectiveness of a strategy to re-culture urine upon completion of therapy and re-treatment of those still found to have asymptomatic bacteriuria was not evaluated in this review. A suggested association between anaemia and asymptomatic bacteriuria in pregnancy was not considered in the review as an outcome.
Many of the included trials had methodological weaknesses, such as inadequate concealment of allocation, which could introduce bias. Not all of the antibiotics used in the studies included in the review are currently in use.
All adequately controlled trials, which could be identified, have been included and appropriately analysed.
2. RELEVANCE TO UNDER-RESOURCED SETTINGS
2.1. Magnitude of the problem
The prevalence of asymptomatic bacteriuria in pregnancy is quoted to be between 5% and 10% 1). Race-specific rates show significant variation (2, 3, 4.) Estimates from mathematical modelling to evaluate the cost–effectiveness or cost–benefit of different diagnostic strategies vary significantly, being around an incidence rate of 9%, when pyelonephritis is considered as an outcome (5). It is therefore important to evaluate the prevalence of asymptomatic bacteriuria in a specific population.
2.2. Applicability of the results
In spite of the fact that the most recent trial included in this review was published in 1987 and most others in the sixties, the results of the review should be applicable in all settings.
2.3. Implementation of the intervention
Difficulties in implementation this intervention may arise at several different levels. First, the health care provider has to have increased awareness of the importance of asymptomatic bacteriuria (6). Educational programmes that promote the availability of antenatal care and emphasize the importance of an early first antenatal visit (<28 weeks of pregnancy) to the health centre are paramount to the successful implementation of this intervention.
Perhaps most importantly, the availability of adequate diagnostic tools for asymptomatic bacteriuria should be ascertained. In many developing countries, financial constraints may restrict the feasibility of introducing general screening of all pregnant women. Facilities to culture bacteria from a midstream clean-catch sample, still considered the best diagnostic test may not be available in all settings.
Where screening is available, treatment of asymptomatic bacteriuria would be feasible in most settings. However, resource limitations in terms of access to antibiotic therapy in some settings, as well as inadequate compliance with treatment, can make this intervention difficult to apply. The use of less expensive antibiotics, based on susceptibility testing, such as nitrofurantoin and those with potentially less side-effects, will increase the likelihood of success in implementing this intervention. The most effective length of treatment has not been determined (7).
More information is needed about the prevalence of asymptomatic bacteriuria in different populations, at different gestational ages, as well as recurrence rates in those completing treatment. Further clarification of the importance of lower colony counts in urine culture, than those currently used for diagnosis of asymptomatic bacteriuria, and their associations with pyelonephritis have to be explored.
The diagnostic characteristics (sensitivity, specificity, etc.) of screening tests for asymptomatic bacteriuria, which could be equal or better in diagnostic accuracy than quantitative urine culture, but are less expensive or complex, is an area where research efforts should focus on (8, 9)
The correlations that might exist between asymptomatic bacteriuria and other infections of the genitourinary tract during pregnancy and their association with low-birth-weight and or preterm birth need further study. Since the available information shows a significant decrease in pyelonephritis with antibiotic therapy, it will not be ethical to conduct controlled trials comparing an antibiotic against a placebo in women diagnosed with asymptomatic bacteriuria. Randomized controlled trials should be conducted to test which currently available antibiotic regimen(s), are as or more effective, less expensive, produce less side-effects and improve compliance (7).
Sources of support: Thomas Jefferson Medical College, Thomas Jefferson University, Department of Obstetrics and Gynecology, Divisions of Research in Reproductive Health and Maternal Fetal Medicine, Philadelphia, PA, USA.
Acknowledgement: This commentary was revised by the RHL Editorial Team to keep it up-to-date with the current version of the Cochrane review.
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This document should be cited as: Tolosa JE. Antibiotics for asymptomatic bacteriuria in pregnancy: RHL commentary (last revised: 14 January 2008). The WHO Reproductive Health Library; Geneva: World Health Organization.