A flash-heating technique may kill HIV particles in breast milk, allowing HIV-positive mothers to breast feed more safely, researchers from the University of California say.
Kiersten Israel-Ballard of the Univesity of California, who conducted the study, says that flash-heating may have a special role to play during the transition from exclusive breastfeeding to solid foods. Mixed feeding of breast milk and other foods has been shown to carry a higher risk of HIV infection than exclusive feeding, possibly because allergens in solid foods cause inflammation in the infant's gastrointestinal tract, increasing vulnerability to HIV infection from breast milk.
On the other hand, abrupt weaning from the breast has been associated with growth faltering and an increase in HIV levels in breast milk. Any subsequent return to breast feeding may therefore carry a higher risk.
“Milk production would be well established after months of EBF, and other complementary foods would then be an additional source of infant nutrition. If a mother fed heat-treated breast milk to her infant several times each day while introducing complementary foods it could significantly impact the infant’s nutritional intake as well as provide immune protection unique to breast milk, thus lowering risk of morbidity from non-HIV diseases.”
“While some mothers may provide heated milk only for weeks and others for months, the contribution to the infant’s health outcomes during this transition phase could still be substantial.”
Around 40% of the 700,000 children who become infected with HIV each year contract the virus by means of prolonged breast-feeding. Completely avoiding breast-feeding is not an option for many HIV-positive mothers in resource-poor areas.
Since WHO recommends exclusive breastfeeding with modifications in these areas, Kiersten Israel-Ballard (University of California, Berkeley, USA) and South African and Canadian colleagues decided to examine one recommended strategy of pasteurisation, by evaluating a more practical but experimental technique to that recommended by WHO – flash heating of breast milk.
The team studied ninety-eight breast milk samples, collected from 84 HIV-positive mothers in South Africa. Each sample was separated into two: one for flash-heating and one as an unheated control.
For the standardised flash-heating protocol, milk was placed into an uncovered sterile jar in a large pan containing 450ml of water. The water was heated to a rolling boil with a butane stove and then removed immediately to cool to 37 degrees. All materials were uniform and locally sourced to provide a naturalistic process of flash-heating. Samples were then frozen and analysed in the USA. Reverse transcriptase (RT) assays (lower detection limit of 400 copies/ml) were performed to differentiate active versus inactivated cell-free HIV in unheated and flash-heated samples.
The team report that detectable HIV was found in breast milk samples from 26 of 84 (31%) mothers. After adjustment, multivariate logistic regression showed statistically significant associations between detectable virus in the control samples of breast milk and lower maternal CD4 counts (p = 0.045), reduced volume of breast milk expressed, and a positive association with use of multivitamins (p = 0.03). Multivitamin use was linked with increased milk volumes, but the authors acknowledge other factors not measured, such as stress, could reduce milk volumes. All flash-heated samples showed undetectable levels of cell-free HIV-1 by the RT assay (p < 0.00001).
“It's important to clarify that heat treatment of breast milk has been a WHO recommended infant feeding option for years,” said Kiersten Israel-Ballard. “Our acceptability data tells us that some mothers (not all) would try this method, if indeed there was a practical method that they could realistically use. Actually, it was mothers in Zimbabwe who initially inspired this work when they asked what they could do to their breast milk to make it safe.”
“We have found that many mothers are used to this way of heating since using a water bath is how they commonly heat their cow's milk,” she added. “The concept of heating but not destroying the protective elements in the milk is not a new one, even to mothers in rural Africa. The breastmilk is immediately removed from the water, covered, and allowed to cool and then cup or spoon-fed to the infant.”
“Field observations using local stoves, utensils, pans, and jars and varying water and milk volumes in South Africa, Kenya and Tanzania have shown that this protocol can be adapted as long the water is approximately two finger-widths above the level of the milk.”
Some have questioned whether the frequency of manual expression of breast milk required is practical and acceptable for mothers.
“Manual expression is already a technique that should be taught for healthy exclusive breastfeeding and is actually a criteria for Unicef Baby Friendly Hospitals, “ Dr Israel-Ballard told aidsmap. “So if manual expression is taught - as it should be - to all mothers to avoid mastitis, then when it comes to weaning, manual expressing is a more healthy way to accomplish this - it avoids inflammation and pain from engorged breasts.”
“Flash-heat seems to have the most realistic place during this transition period - when a mother chooses to begin feeding complementary foods she would manually express her milk and then heat it as many times a day as she is able and for as long as possible. If she has already been taught manual expression, this would not be a cumbersome task to ask of a mother.”
“Even if she were to do this two to three times per day for a few weeks or a month that could significally impact the nutritional intake for the infant, not to mention the much-needed immune protection during this high risk period.”
“The most challenging piece of this is that mothers may need support to not only continue exclusive breastfeeding, as we well know from studies, but also to continue Flash-heat. We are currently working on feasibility studies to ascertain how much support a mother might need.”
Some uncertainties remain about how effectively the heating method eliminates infectious virus particles from breast milk. The cut-off level of the RT assay could mean that low levels of cell-free HIV persist, but the authors point out that reverse transcriptase is one of the components of HIV most resistant to heat.
In comparison, the envelope proteins of the virus, which are essential if the virus is to infect human cells, are much more easily damaged and degraded by heat. In other words, measuring reverse transcriptase levels after heating would likely lead to an over-estimate of any remaining viral activity, the authors believe.
They also acknowledge lack of data on cell-associated infectious virus. If flash-heating is used in such communities “we caution that the heating protocol described here should be strictly adhered to until additional field tests and thermal inactivation studies are completed and we better understand the margin of heating error allowable to ensure HIV destruction”, the authors write.
In conclusion, this preliminary study suggests that flash-heat can inactivate HIV in naturally infected breast milk from HIV-positive women. “Field studies are urgently needed to determine the feasibility of in-home flash-heating breast milk to improve infant health while reducing postnatal transmission of HIV in developing countries,” urge the authors.
Reference
Israel-Ballard K et al. Flash heat inactivation of HIV-1 in human milk. A potential method to reduce postnatal transmission in developing countries. J Acquir Immun Defic Syndr 45 (3): 318-323, 2007.