Her mother was killed, but miraculously, Teresa survived the accident unharmed. Since then, life has continued to present her with challenges.

At 16 years old, Teresa lost her father, became pregnant and had to drop out of school. After a second child was born, her husband asked her to leave their home because, said Teresa, they "were always arguing." And last year, with her third pregnancy, the 29-year-old learned she was HIV-positive.

"I was attending the clinic when the nurse explained to us about the possibility of having an HIV test. I was in good health, so I thought I was OK. It was painful when I found out I was HIV-positive, but I managed to control myself," said Teresa, who did not want her real name to be used.

A lot has happened since then. While being interviewed, she breastfed and played with her robust, gurgling five-month-old baby boy as she waited for him to be weighed at a bustling health clinic in Machava, a suburb of Mozambique’s capital, Maputo.

Teresa is enrolled in a pioneering "prevention of mother-to-child-transmission" (PMTCT) project supported by an Italian organization, Sant’Egidio, under an agreement with the government of Mozambique. There she learned that babies of HIV-positive women can become infected in any of three ways: the virus can be transmitted during pregnancy, in the process of childbirth, or through breastmilk.

Without any PMTCT, there is a 30 per cent chance that an infected mother’s baby will also be positive. The good news is that administering a dose of anti-retroviral medication to the woman during labour and to the baby just after birth – the procedure followed in most of Mozambique’s government-supported PMTCT programmes – reduces that risk by half. Infant feeding decisions then become critical to ensuring that a baby who escaped infection will remain HIV-free.

Teresa was lucky enough to enroll in a pilot project that goes a crucial step beyond child survival to keep mothers healthy. Through PMTCTplus, a pregnant HIV-positive woman at the Machava clinic can also receive "Highly Active Anti-Retroviral Therapy" or HAART. This triple-dose combination of AIDS drugs helps maintain her own health and reduce her "viral load," or the amount of HIV in her system, throughout pregnancy and for the next six months while she feeds her baby nothing but breastmilk.

Women whose initial tests during pregnancy showed that their immune cell levels (known as CD4 counts) had dropped dangerously low – under 250 – stay on HAART even after breastfeeding ends.

It has long been known that breastmilk carries HIV, and preliminary research suggests that an all-or-nothing feeding regimen is safest.

Babies who are breastfed exclusively, taking nothing else by mouth, appear able to digest HIV-tainted breastmilk without having the virus pass into their systems. Babies fed exclusively by bottle, with breastmilk substitutes such as infant formula, water, juice and tea, completely avoid the risk of contracting HIV through breastmilk (although they are deprived of critical benefits of breastfeeding, and are susceptible to the diarrhoeal and other diseases that bottle-feeding can cause.)

It is the combination of breastfeeding and bottle-feeding, or "mixed feeding," that concerns nutritionists most: an infant’s tiny gut isn’t made to tolerate anything but mother’s milk, and it’s possible that onc