USPSTF calls data “insufficient” on benefits and harms of screening for bacterial infection

An update to guidelines by the U.S. Preventive Services Task Force (USPSTF) offered little support for screening pregnant persons who do not have signs or symptoms of bacterial vaginosis.

The task force recommended against screening for bacterial vaginosis in pregnant persons not at increased risk for preterm delivery (“D” grade; “no net benefit”), and concluded that there is currently not enough evidence to assess the balance of benefits and harms of screening for bacterial vaginosis in pregnant persons (“I” statement; “evidence is insufficient”).

The recommendation is in line with the task force’s 2008 guidelines but does contain some language changes, specifically the use of the term “pregnant persons” to include transgender individuals, and an emphasis that it applies only to screening for asymptomatic bacterial vaginosis, explained Douglas K. Owens, MD, MS, Stanford University in California, and task force members, in JAMA.

They also highlighted that the USPSTF guidance matches those of other professional groups, such as the American College of Obstetricians and Gynecologists, the CDC, and the American Academy of Family Physicians, all of which are against routine screening for bacterial vaginosis in asymptomatic pregnant women.

While “bacterial vaginosis is often asymptomatic, can resolve spontaneously, and recurs often, with or without treatment,” Owens’ group noted, “Most clinicians treat symptomatic bacterial vaginosis in pregnancy.”

They acknowledged that “bacterial vaginosis during pregnancy is associated with a 2-fold higher odds for preterm delivery, [but] it is not clear that bacterial vaginosis is a cause of preterm delivery.”

Additionally, African-American race is tied to both bacterial vaginosis and preterm delivery, as are “young age, nulliparity, current tobacco use, low educational attainment, lower income, and concurrent sexually transmitted infections,” they stated.

Again, “Even when these risk factors are present, it is unclear whether screening and treating asymptomatic bacterial vaginosis in pregnant persons at increased risk for preterm delivery prevents preterm delivery,” the task force members said.

The diagnosis and management of bacterial vaginosis during pregnancy “is particularly important in light of growing concerns about the effects of antibiotic use on long-term maternal and child health because of effects on their microbiomes,” noted Amanda L. Lewis, PhD, of the Washington University School of Medicine in St Louis, and Louise C. Laurent, MD, PhD, of the University of California San Diego, in an accompanying editorial.

However, research on the pros and cons of screening and treatment of this condition have not necessarily kept apace, they pointed out. “This issue was last addressed by the USPSTF more than a decade ago,” Lewis and Laurent wrote. “Since then, only 1 additional large clinical study on the topic has been published.”

They stressed there are many questions that still need answers regarding the issue are:

  • Is there enough data on “what bacterial vaginosis is and how it is mechanistically linked to preterm birth”?
  • Which pregnant persons are “at risk” for bacterial vaginosis, and would they benefit from treatment to prevent preterm birth?
  • Are antibiotic treatment strategies useful for preventing preterm birth?
  • Do “standard clinical treatments for bacterial vaginosis [target] the desired bacterial populations”?
  • What is the treatment adherence, efficacy, or recurrence of bacterial vaginosis?

The updated guidelines are based on an evidence report by Leila C. Kahwati, MD, MPH, of RTI International in Research Triangle Park, N.C., and co-authors. They evaluated published data through December 2019, including randomized clinical trials (RCTs), intervention studies (only for harms), and meta-analyses of metronidazole or clindamycin.

Ultimately, 48 publications were included in the review, none of which assessed the harms of screening. Kahwait’s group found that, among trials that reported findings from general obstetric populations, there was no significant association seen between treatment and spontaneous delivery before 37 weeks (pooled absolute risk difference –1.44%, 95% CI -3.31%-0.43%) or any delivery before 37 weeks (pooled ARD 0.20%, 95% CI -1.13%-1.53%).

In trials with findings among women with a prior preterm delivery, three of five showed a meaningful benefit. Across RCTs, maternal adverse events (AEs) from treatment were minor and uncommon, such as candidiasis, but were seen slightly more often with active treatment versus placebo.

Two meta-analyses of observational studies reported no significant link between metronidazole exposure and congenital malformations (odds ratio 0.96, 95% CI 0.75-1.22; OR 1.08, 95% CI 0.90-1.29).

Also, a cohort study reported no significantly increased incidence of childhood cancer among children exposed to metronidazole (adjusted relative risk 0.81, 95% CI 0.41-1.59), although “studies of in utero exposure had important limitations,” according to the authors, such as merely “fair methodological study quality,” imprecise estimates because instances were rare, and the fact that exposure during pregnancy was evaluated across a range of medical indications, and was not specific to bacterial vaginosis treatment.

Overall, Kahwait and co-authors declared that, for diagnostic accuracy, the strength of evidence was low based on “fair methodological quality and inconsistency. Most studies were conducted among symptomatic, nonpregnant women; thus, the applicability to asymptomatic pregnant women is not clear.”

In addition, in a general obstetric population, “the strength of evidence was moderate for no benefit of treatment on all-cause preterm delivery because of imprecision and low for no benefit of treatment on spontaneous preterm delivery because of imprecision and inconsistency.”

And among women with a prior preterm delivery, the strength of evidence for preterm delivery at <37 weeks was “insufficient because of inconsistency and imprecision.”

Finally, compared with placebo, “the strength of evidence for serious maternal [AEs] related to treatment was moderate for no difference for oral metronidazole and both oral and intravaginal clindamycin.”

In a JAMA Patient Page, Jill Jin, MD, MPH, of Northwestern Medicine in Chicago, highlighted messaging for physicians to their patients:

  • The USPSTF conclusion that screening for bacterial vaginosis in asymptomatic pregnant women, and who are not at increased risk of preterm delivery, has no general benefit, is made with “moderate certainty.”
  • Treatment for bacterial vaginosis during pregnancy does not seem to help prevent preterm delivery, but it is unknown if bacterial vaginosis causes an increased risk of preterm delivery.
  • While screening to diagnose bacterial vaginosis in asymptomatic women is not likely to cause harm, antibiotic treatment for the condition can lead to AEs (stomach discomfort, vaginal yeast infections).
  1. The U.S. Preventive Services Task Force recommends against screening for bacterial vaginosis in pregnant persons not at increased risk for preterm delivery.

  2. The task force concludes that current evidence is insufficient to assess the balance of benefits and harms of screening for bacterial vaginosis in pregnant persons at increased risk for preterm delivery.

Shalmali Pal, Contributing Writer, BreakingMED™

USPSTF is funded by the Agency for Healthcare Research and Quality (AHRQ). All USPSTF members reported travel reimbursement and an honorarium for participating in USPSTF meetings. A co-author reported support from, and a relationship with, Healthwise.

Lewis reported grants from the NIH, Burroughs Wellcome Foundation, and National Institute of Allergy and Infectious Diseases, as well as relationships with Metrodora, Toltec Pharmaceuticals, Tennor Therapeutics, and Talis Biomedical.

The evidence report was funded by AHRQ.

Owens, Laurent, Kahwati and co-authors, and Jin reported no relationships relevant to the contents of this paper to disclose.

Cat ID: 191

Topic ID: 83,191,730,191,41,138,192,925