Breastfeeding is particularly important if a child has pertussis, as it's
the only way he/she will be provided any immune protection against what
otherwise can be a devastating illness in young infants, and for which
treatment does not benefit the individual once the disease is
recognizable (i.e. coughing paroxisms), as noted in another e-mail on the
list today.  Infants usually get exposed through adult contacts, to which
the mom has also likely been exposed and therefore will generate an immune
response specifically against pertussis and pass this invaluable
protection on to the very vulnerable infant.  Regarding exposure to the
antibiotic via breastmilk, the whole family (including the child) would
be ingesting the antibiotic anyway (to minimize spread to others, as it
benefits an individual only if taken very early in the course, ususally
before the disease is distinguishable from other URIs).

MaryAnn O'Hara, MD, MSt, U-Washington