CMV Remains a Concern Because of Lack of Research

Christopher Zahn, MD; Brenna Hughes, MD, MSc


December 02, 2016

Cytomegalovirus (CMV) is the most common congenital viral infection. A recent article in the New York Times drew important attention to the disease. The article highlights the stories of four families tragically affected by the virus. Although CMV is a serious illness for consideration by ob/gyns and expecting mothers, there is quite a bit of nuance and detail to understand about CMV research and preventive guidelines that are not captured in the New York Times article.

It is important to understand the risks for CMV transmission and outcomes. About 1 in every 150 infants is born with congenital CMV infection. However, only about 1 in 5 with congenital CMV infection will be symptomatic.[1] Although rates of exposure and infection are relatively high, quality research on the topic has been frustratingly limited. Historically, women's healthcare providers have relied upon weak research to dictate guidelines for prevention—mostly hygiene measures, such as increased handwashing and avoiding contact with children (including kissing them).

At the American College of Obstetricians and Gynecologists (ACOG), our aim is to incorporate the highest-quality evidence in all of our recommendations; however, in the absence of high-quality data, lower-quality research may be considered, often with support from expert opinion. In the case of hygiene measures for CMV prevention, the existing data are of low quality.

The highest quality of research is a randomized controlled trial. No published randomized trials have examined the impact of hygiene measures to prevent maternal acquisition of CMV. The only randomized trial was done in conjunction with the Centers for Disease Control and Prevention, and the outcome was change in maternal behavior, not CMV acquisition.[2] This study brought both new understanding and the most reliable data to guidance for CMV prevention and treatment. As a result, in 2015, ACOG reviewed and updated our CMV guidelines, determining that our prior recommendation of increased hygiene measures was not supported by the quality of the existing data.[3,4,5]

The Problems With 'Hygiene Measures'

For some, this raises the question, "What's the harm in advising women to wash their hands more often?" The term "hygiene measures," however, includes much more than simple handwashing and could lead pregnant women to avoid physical contact with their own children. Over the years, we have found that recommendations are sometimes made because they seem like they "just make sense"; however, when that principle is applied, there may be unintended consequences that result in harm, with no clear corresponding benefit as a result of the intervention.

In the case of CMV, we see that the burden of preventive techniques varies. Whereas some suggestions, such as handwashing, are innocuous, others are much harder or impractical, or even unpleasant, to implement—for example, refraining from kissing your baby or toddler or wearing gloves while handling your child. CMV prevention advice could be recommended once we know whether it is effective. The risk for harm at this time relates to a mother's ability to bond with her children, rather than more easily adopted tactics typically recommended during pregnancy, such as avoiding certain groups of foods or changing kitty litter.

In addition, implementing unproven hygiene measures can falsely reassure patients. Giving "just makes sense" advice may mislead women into believing that incorporating hygiene measures will change the risk for CMV transmission, or perhaps eliminate it, when in fact this is not the case.

When it comes to a discussion between doctors and patients about potential concerns, physicians try to answer all of their patients' questions during pregnancy to the best of their ability. This includes everything from consumption of diet soda or fish to influenza vaccination, Zika infection, diabetes, preterm labor, and HIV. Out of necessity, both physicians and patients tend to focus on conditions for which there is a proven intervention to address either prevention or treatment. In the case of CMV infection, these data are still unknown and lacking adequate research. Until that research is more firmly developed, it is, unfortunately, unlikely that physicians or patients will give significant discussion time to congenital CMV infection.

A Lack of Funding

This understanding of the doctor/patient dialogue led the New York Times to ask, "Why, then, do we counsel pregnant women about Zika?" It is understandable to draw this parallel, because Zika and CMV both lack known effective interventions. Zika, however, presents a much different public health demand than CMV, for several reasons.

With CMV, we know that even when a fetus is infected in utero, 90% are asymptomatic at birth, although some go on to develop sequelae. We also know that 40% of fetuses are infected when maternal infection occurs. And we know that fewer than 1% of women acquire CMV during pregnancy.[6,7] For the Zika virus, we don't know the prevalence, how many fetuses will become infected if the mother is infected, or how likely the fetus is to be severely affected if infected.

There is one very notable and important difference in how we handle Zika virus vs CMV: funding. The New York Times rightly points out the irony that Zika virus routinely makes the evening news, whereas CMV, which affects thousands of US infants annually, is virtually unheard of, especially when it comes to research funding. Congress approved $1 billion to support Zika virus research and prevention, but CMV does not have a line item for funding in the annual budget.

The lack of progress in combating CMV is not because "...obstetricians do not feel it is important or even worthy to educate pregnant women about CMV," as the infectious disease physician quoted in the article suggests, but because research is inadequately funded to develop effective prevention and treatment strategies. This is a priority for ACOG and many ob/gyns across the United States. Governmental and pharma research funding to support these efforts is long overdue.

ACOG is the nation's leading group of healthcare providers dedicated to caring for women. We are committed to the health of every mother and baby, which includes providing evidence-based guidance for our members advising women about CMV and continued research and development to bring an end to CMV entirely.


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