Household income has been shown to interact with child growth in Brazil.21 A US study of
diarrhoeal disease found no interaction between breast feeding and household income.8 Household income, like social class, may not be a good marker of transmission risk.
Importantly, we
found that in infants currently formula fed, having been breast fed for at least six months was not associated with less
diarrhoeal disease than having never been breast fed.