Eradication of Cytomegalovirus from Human Milk by Microwave Irradiation: A Pilot Study

Introduction

The Section on Breastfeeding of the American Academy of Pediatrics recommends the use of human milk (HM) feeding in very-low-birth weight premature infants. ¹ It is known that fresh HM can transmit cytomegalovirus (CMV) to the newborn, although the risks are not well defined. In a recent Editorial, Jobe noted that freezing or pasteurizing the milk may limit CMV transmission, although such manipulations may change functional milk properties. ² Jobe stated that “it remains to be determined if the possible benefits of feeding preterm infants fresh CMV positive milk is worth the probable risks to some infants.” ² We conducted the current pilot feasibility study to compare two previously reported freezing methods used to neutralize the virus in breast milk,^3,4 and one not tested to date, that is, microwave exposure.

Materials and Methods

In this controlled laboratory trial, HM samples were collected from 31 CMV-IgG- or CMV-IgM-seropositive consecutive volunteer mothers of infants hospitalized at the Lis Maternity Hospital. Mothers provided their consent to participate and the study was approved by the local institutional review board. Twenty-five milliliters of HM samples were obtained 10–50 days after delivery using a breast pump (Medela AG, Baar, Switzerland) and were stored into sterile glass jars. All 31 milk samples were aliquoted in five 5 mL samples. One aliquot was tested for CMV antigen detection using the Shell-Vial method. ⁴ Samples positive for CMV Ag were further considered for viral neutralization. The second and third aliquots were frozen at −20°C for 1 and 3 days, respectively. The fourth aliquot was placed in a plastic stand in the center of a standard commercial microwave oven (maximum output 750 W at 2450 mHz; Brother Model BR 790 XL, China) and exposed to microwave irradiation for 30 seconds at a low-power setting (500 W). The fifth aliquot was exposed similarly for 30 seconds at a high-power setting (750 W). The temperature of the samples was measured immediately after irradiation while stirring the milk with a thermometer (LW thermometer, Germany) and until stabilization of the temperature (within 30 seconds). All aliquots were tested for the presence of CMV Ag after treatment using the Shell-Vial method.^3,4

Results

Thirty-one samples were collected, and 15 were found to be positive for CMV Ag. A 1-day freezing at −20°C eradicated CMV Ag presence in 12/15 samples (20% failure rate). A 3-day freezing at −20°C eradicated CMV Ag presence in 14/15 samples (7% failure rate). A low-power 30-second microwave treatment eradicated CMV Ag presence in 13/15 samples (13% failure rate). A high-power 30-second microwave treatment eradicated CMV Ag presence in 15/15 samples (0% failure rate). By the end of the low-power 30-second microwave treatment session, samples reached a temperature of 42.6°C ± 6.0°C (range: 30–52°C), whereas by the end of the high-power 30-second microwave treatment session, samples reached a temperature of 76.5°C ± 4.9°C (range: 72–85°C).

Discussion

In this pilot preliminary study of 15 samples of CMV-contaminated HM, high-power 30-second commercial microwave treatment was 100% effective in eradicating CMV Ag. Low-power treatment was not 100% efficient in eradicating CMV Ag detection, whereas 1-day freezing at −20°C had a 20% failure rate and 3-day freezing had a 7% failure rate.

The medical literature offers several neutralization techniques for CMV-infected breast milk.^2–4 Freezing milk samples at −20°C for 3 days neutralizes many, but not all samples,^3,4 a point verified by the current study. Maschmann et al. showed that treatment of milk samples for 5 and 15 seconds under high temperature (72–82) may be an effective way of neutralizing the virus without destroying some unique nutritional and immunologic qualities of HM. ⁵ However, the methodology of rapid high-temperature treatment requires the use of a special equipment not necessarily available everywhere. We suggest from this pilot study that microwave treatment of HM at a high-power setting might be a promising way for CMV eradication.

Further studies are required to (1) confirm on a larger number of HM samples that high-power microwave treatment allows for 100% efficacy in eradicating CMV and (2) test the possible effects on the cellular, immunologic, and nutritional properties of breast milk that may result from processing milk under these specific conditions. The effect of microwave radiation on human milk nutrients or bio active components has been very little studied and has shown a decrease in immunoglobulins content with apparent no change in fatty acid composition. ⁶ Nevertheless, if microwave treatment of human milk is to be used, we caution about the need of appropriate time of cooling, in order to prevent potential burns.