According to the World Alliance for Breasfeeding Action (WABA), we already have evidence of harm to infants when exclusively formula fed. In a 1 December 2006 (World AIDS Day) press release, they relate the following:

A stark reality check from Botswana early this year showed how horribly things can go wrong when bottlefeeding becomes well entrenched in an African country. When the national PMTCT programme was launched in 1999 a UNICEF-funded survey showed that only 3% of children were never breastfed; 55% were breastfed until 24 months, 7% until 35 months, and 2% until 59 months. In an effort to prevent paediatric HIV infection, and as one of Africa’s wealthiest countries, with a water supply generally regarded as safe, Botswana recommended replacement feeding by all HIV-positive women, accompanied by provision of a year’s supply of free formula.5 Its success in providing free PMTCT services to a higher percentage of pregnant mothers than any other country has been hailed as an example for the rest of Africa to follow. Today, one-third of pregnant women are living with HIV and ~98% of HIV-infected mothers formula-feed their babies. Indeed, formula has been promoted so strongly that one in five uninfected or untested mothers have also stopped breastfeeding before their babies reach six months of age.
But late last year Botswana suffered a catastrophic outbreak of gastrointestinal illness. Hospitals throughout the country were overwhelmed by 35 000 cases and 532 deaths. The most affected group was infants aged 0 – 12 months who were not breastfed. Assistance was requested from the US Centers for Disease Control, WHO and UNICEF. A closer evaluation found that a variety of pathogens was responsible, including cryptosporidium, enteropathogenic e coli and salmonella. Over half the affected infants were already malnourished, and despite mothers returning to the clinic several times per month, had received only 51% of the quantity of formula they needed before their illness. However, the most significant risk factor was that 93% were not breastfeeding, resulting in a 50-fold higher risk of diarrhoea and an 8-fold risk of dying from diarrhoeal illness.9 The final death toll remains unknown, since many babies died at home, with one village reporting the loss of 30% of its formula-fed babies.

Risk factors for transmission from mother to child via breastfeeding include the following:

Mother:
• Immune/health status
• Plasma viral load
• Breastmilk virus
• Breast inflammation (mastitis, abcess, nipple lesions)
• New HIV infection

Baby:
• Breastfeeding duration
• Non-exclusive breastfeeding
• Age (first months)
• Lesions in mouth, intestine (like thrush)
• Prematurity
• Infant immune response