Prepared by Lindsay E. Nicolle, MD, Department of Medicine, University of Manitoba
Objective
To make recommendations for screening women who are pregnant for bacteriuria
in Canada.
Burden of Suffering
The prevalence of asymptomatic bacteriuria in pregnancy varies from
4-7% and is similar to that observed in non-pregnant women. The prevalence
is higher among individuals in lower socioeconomic classes, and those with
a past history of asymptomatic urinary infection. There is a high
incidence of pyelonephritis occurring later in pregnancy in women with
asymptomatic bacteriuria identified and not treated early in pregnancy.
13% of untreated women with asymptomatic bacteriuria developed pyelonephritis,
compared with 0.4% of those with negative screening cultures. Women
with urinary infection (UTI) associated pregnancy have been shown to have
higher fetal mortality rates, and increased risk of low birth weight and
prematurity.
Options
Screening options include bacterial culture of urine, urinalysis, and
dipslide method. The treatment strategy for women who have bacteriuria
is antibiotics.
Outcomes
Sensitivities and specificities of the tests, development of pyelonephritis
in pregnant women, cure rates, intra-uterine growth retardation, low birth
weight, stillbirth, and premature delivery of the infant. Costs were mentioned
briefly.
Evidence
MEDLINE was searched to 1993 using the keywords urinary tract infections,
pregnancy, human and case reports.
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993. Consensus was reached on final recommendations.
Benefits, Harms, and Costs
The gold standard for screening for asymptomatic bacteriuria is urine
culture from women early in their pregnancy (12 to 16 weeks). Nonculture
methods such as urinalysis and leukocyte-esterase dipstick are not reliable.
Compared with semi-quantitative culture, the dipslide method is less costly
and less prone to error. For women with asymptomatic bacteriuria a second
sample is required for determination in the laboratory using quantitative
culture for confirmation of bacteriuria, identification of organisms, and
antimicrobial susceptibility testing. Optimal time for screening is at
12 to 16 weeks' gestation; this will identify 80% of women who will ultimately
have asymptomatic bacteriuria during pregnancy.
All but 1 study showed that women who tested positive for bacteriuria and were treated had a decrease in the incidence of pyelonephritis from a range of 20% to 30% to a range of 2% to 4%. 1 study showed that screening with a single urine specimen in early pregnancy was cost effective as long as the population prevalence of bacteriuria was > 2%.
A meta-analysis of 8 studies showed that treatment of asymptomatic bacteriuria reduced the risk for low birth weight (relative risk 0.56, 95% CI 0.43 to 0.73); this antibiotic treatment might, however, be associated with subclinical chorioamnionitis rather than bacteriuria. Other pregnancy related outcomes have insufficient evidence for recommendations to be made.