2014 Update on infectious disease

Hooton and colleagues concluded that the presence of E coli on a midstream culture, even in low colony counts, is predictive of true bladder infection, as determined by catheterization. However, enterococci and group B streptococci were more likely to be vaginal contaminants or associated with coinfection with E coli, or bot.

What this EVIDENCE means for practiceThe findings of Hooton and colleagues have several key implications for practicing clinicians:
• When either a pregnant or nonpregnant patient experiences her first episode of acute cystitis, the overwhelming probability is that E coli is the infecting pathogen. We can reduce costs by empirically treating the initial infection, thereby avoiding the expense of a urine culture.
• For patients with recurrent infections or for immunocompromised patients, a culture and sensitivity test should be performed because other uropathogens are more likely to be involved and may have less predictable antibiotic susceptibility patterns.
• Contamination of supposed “clean-catch” specimens is very common, and the cultures resulting from these specimens can mislead us in our decisions about antibiotic therapy. Enterococci and group B streptococci are more likely than not to be contaminants from the vaginal flora rather than true infecting pathogens. When they are present in the bladder, they are usually associated with E coli. Accordingly, E coli should be the principal target of anti­biotic therapy.
• To avoid concerns about contamination of specimens in acutely symptomatic patients, obtain the urine specimen by catheter. In the catheterized specimen, the cutoff for true bladder infection should be ≥100 colonies/mL. The cutoff of ≥100,000 colonies/mLis applicable only for clean-catch specimens obtained from asymptomatic patients.
• Clinical laboratories should embrace the new cutoff and report even seemingly low colony counts when the urine sample has been obtained by catheterization.

In preterm labor, amniotic fluid infection without inflammation does not necessarily predict a poor fetal outcome

Combs CA, Gravett M, Garite TJ, et al. Amniotic fluid infection, inflammation, and colonization in preterm labor with intact membranes. Am J Obstet Gynecol. 2014;210(2):125.e1–e15.

In this very important clinical investigation, Combs and colleagues collected amniotic fluid from 305 women with preterm labor. They then measured the amniotic fluid concentration of interleukin-6 (IL-6) and assessed for the presence of microbial invasion of the amniotic cavity (MIAC) by either culture or detection of microbial 16S ribosomal DNA. Based on these test results, investigators divided the patients into five groups:

• Infection—defined as positive MIAC and IL-6 >11.3 ng/mL
• Severe inflammation—negative MIAC and IL-6 >11.3 ng/mL
• Mild inflammation—no MIAC and IL-6 from 2.6 to 11.2 ng/mL
• Colonization—positive MIAC and IL-6 <2.6 ng/mL
• Negative—no MIAC and IL-6 <2.6 ng/mL.

The end points of the investigation were latency period and composite perinatal morbidity and mortality. Perinatal morbidity included respiratory distress syndrome, grade 3 or 4 intraventricular hemorrhage, necrotizing enterocolitis, and culture-proven neonatal sepsis.

Related article: Does treating asymptomatic bacterial vaginosis reduce preterm delivery? Hyagriv N. Simhan, MD, MSCR (Examining the Evidence; April 2008)

Interestingly, the infection and severe inflammation groups had similar short latency periods (median of <1 and 2 days, respectively) and similar rates of composite perinatal morbidity and mortality (81% and 72%, respectively).

The colonization and negative groups also had similar latency periods (median of 23.5 and 25 days, respectively) and similar rates of composite morbidity and mortality (21% and 25%, respectively).

The mild inflammation group had intermediate outcomes.

When Combs and colleagues used multivariate analysis to adjust for gestational age at enrollment, amniotic fluid IL-6 concentrations greater than 11.3 ng/mL and in the range of 2.6 to 11.3 ng/mL—but not MIAC—were associated with increased composite perinatal morbidity and mortality.

What this EVIDENCE means for practiceThis study offers several critically important take-home messages:
• Bacterial colonization of the amniotic fluid, without actual inflammation, is not necessarily associated with an ominous outcome for the fetus
• Varying degrees of inflammation exist
• The more intense the inflammation, the worse the outcome for the baby
• The logical clinical application of this investigation is to modify our practice so that, when we perform an amniocentesis for patients with preterm labor, we look not only for bacterial growth but for the presence of key inflammatory mediators in the amniotic fluid, such as IL-6
• A rapidly available, inexpensive, and easy-to-perform assay for IL-6 would be invaluable in improving our ability to assess patients for subclinical infection and inflammation
• An important question, of course, is whether early implementation of specific anti-inflammatory therapy could alter the prognosis for the fetus in selected cases.

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