Kathleen

The New England Journal of Medicine Vol 325, No 9 p 593-8 "Postnatal
transmission of Human Immunodeficiency Virus Type 1 from Mother to Infant"
concludes that HIV-1 infection can be transmitted from mothers to infants
during the postnatal period.  Colostrum and breastmilk may be efficient
routes for the transmission of HIV-1 from RECENTLY (my emphasis) infected
(sero-converting) mothers to their infants.  Two infants in this study
acquired their infection (15 and l8 months) late in the lactation period.
Conclusion suggests that the peak viraemia associated with early HIV-1
infection enhances the risk of transmission.

New England Journal of Medicine, 1991, 325 (9), 652-654 "In the vertical
transmission of HIV, timing may be everything" - timing of maternal primary
infection in relation to breastfeeding may be important in the transmission
of HIV (and before delivery) - suggests that current WHO recommendations on
breastfeeding in developing countries NOT be changed.

The Lancet Vol 340, Sept 5 1992 p 585-7 "Risk of HIV type 1 transmission
through breastfeeding" - systematic review of published studies; 4 studies
in which mothers acquired HIV-1 postnatally, the estimated  risk of
transmission  is 29%. 5 studies when the mother was infected prenatally, the
additional risk of transmission through breastfeeding, over and above
transmission in utero or during delivery is 14%.

Hope these are the kind of references you are looking for.  I have later
ones, including that transmission is more likely via colostrum and early
breastmilk, and that risk of transmission increases with duration of
breastfeeding, but they don't give info on when the mother acquired her
infection  so I don't think they give anything new.  If you come across any
later, and more enlightening studies, hope you will share.  Just heard the
startling and horrifying statistic that Zimbabwe is the fourth worst-hit
country for HIV in the world.  l994 study showed that 23% - 34% of all women
delivering in 4 clinics in Harare tested HIV+.  Recent anecdotal reports
that the actual figure now is closer to 50%. The issue of HIV and
Breastfeeding is causing us HUGE concern. Particularly that different
guidelines are given for different populations. We need MUCH more research -
especially on the timing of transmission, e g that "older" HIV infections
(unless the mother has active AIDS) may be less risky (how much less?) to
the breastfed baby.

Pamela, Zimbabwe