Centers for Disease Control and Prevention (CDC) &ndash “When Should a Mother Avoid Breastfeeding ?”
http://www.cdc.gov/breastfeeding/disease/contraindicators.htm

Abstract
While breastfeeding provides the most complete nutrition for infants, including premature and sick newborns, breastfeeding is not advised in certain situations. Staff and pregnant and breastfeeding mothers are encouraged to ask the mother's healthcare provider about breastfeeding in special circumstances.