Over the past couple of years there have been quite a few articles addressing this issue, so I guess it must be important.

The results of all these studies are not consistent, however,

Kelly MS, et al. Postnatal Cytomegalovirus Infection and the Risk for Bronchopulmonary Dysplasia. JAMA Pediatr. 2015;169(12):e153785. In this retrospective cohort of over 100,000 VLBW babies there were only 0.3% that acquired CMV postnatally. Which seems kind of low compared to many prospective studies. CMV acquisition was associated with an increased risk of BPD. I wonder if the diagnosis of CMV might be more likely to be sought out if a baby has BPD, hence biasing the results. Most of the 100,000 babies probably never had screening for CMV.

Brecht KF, et al. Postnatal human cytomegalovirus infection in preterm infants has long-term neuropsychological sequelae. The Journal of pediatrics. 2015;166(4):834-9 e1. This is a relatively small, but in contrast prospective cohort of very preterm babies (<32 weeks). Infants were drawn from a prospective surveillance of CMV re-activation during lactation and transmission to very preterm babies initially published in the Lancet in 2001. In that study, nearly half of the mothers had CMV re-activation and excreted CMV DNA in their breast milk, and over 1/3 of their babies acquired CMV as a result. About half of the babies had symptoms possibly related to CMV. This is why I made the comment about the extremely low numbers of babies with CMV in the first article. The babies from the initial study are now adolescents, and their outcomes were compared to CMV-negative very preterm babies and to term controls. The babies who acquired CMV had lower scores on IQ testing than the CMV-negative preterms, who were lower than the term controls.

Mehler K, et al. High Rate of Symptomatic Cytomegalovirus Infection in Extremely Low Gestational Age Preterm Infants of 22-24 Weeks’ Gestation after Transmission via Breast Milk. Neonatology. 2013;105(1):27-32. In this hospital mothers who deliver small preterm babies are all screened for CMV, and the babies are checked if they got untreated breast milk. In one year they had 22 mothers who delivered at 22 to 24 weeks, 16 of whom were CMV positive; there were 17 babies. 11 of those babies developed CMV infection, 5 of them just had a transient thrombocytopenia, the others had a clinical sepsis like syndrome with or without hepatitis, colitis and various other findings.

Stock K, et al. Pasteurization of breastmilk decreases the rate of postnatally acquired cytomegalovirus infections, but shows a nonsignificant trend to an increased rate of necrotizing enterocolitis in very preterm infants–a preliminary study. Breastfeeding medicine : the official journal of the Academy of Breastfeeding Medicine. 2015;10(2):113-7. This unit in Innsbruck went from pasteurizing its maternal milk, to giving unpasteurized milk in 2010. The results are in the title, and seem as reliable as any retrospective cohort study. You can inactivate CMV by pasteurization, but other impacts on the advantages of breast milk might be negative.

Gunkel J, et al. Predictors of severity for postnatal cytomegalovirus infection in preterm infants and implications for treatment. Expert Rev Anti Infect Ther. 2014;12(11):1345-55. This review article points out that symptomatic CMV is more common in the most immature babies, and it is those below 26 weeks, and especially below 25 weeks who are at very high risk of the short term and negative consequences of CMV.

Summary

CMV infections in very preterm infants are now usually acquired from breast milk.

Donor breast milk is pasteurized and does not carry this risk.

Maternal breast milk has significant advantages to donor milk, but carries an appreciable risk of CMV transmission if the mother has previously had a CMV infection, as the majority of mothers have re-activation of CMV after very preterm delivery.

Pasteurizing maternal breast milk inactivates CMV, but has adverse impacts on the benefits of breast milk.

The most immature infants have the highest rate of CMV acquisition, and the highest rate of significant clinical impacts. Including long-term impacts on intellectual function, and possibly BPD.

Unless you screen mothers and/or breast milk and/or babies for CMV you won’t know how many have acquired CMV, and you probably grossly under-estimate the incidence.

If you do screen, I don’t know what to do with a positive result. ?should we have targeted pasteurization for a subgroup of babies? ?can high-efficiency leukodepletion filters make breast milk CMV-safe without adversely affecting the benefits of maternal milk?

There are still many unanswered questions, but this issue really needs some definitive answers.