title: Late postnatal transmission of human immunodeficiency virus type 1 infection from mothers to infants in Dar es Salaam, Tanzania.
abstract: OBJECTIVE
  To study late postnatal transmission of human immunodeficiency virus type 1 in a cohort of children born to HIV-1-seropositive mothers who delivered at Muhimbili Medical Centre in Dar es Salaam, Tanzania.
  
  
  METHODS
  Since 1991 a prospective cohort study of mother-to-child transmission of HIV-1 has been conducted at Muhimbili Medical Centre in Dar es Salaam. HIV-1-seropositive mothers and age-matched seronegative controls were recruited into the cohort at delivery together with their newborns. Diagnosis of HIV-1 infection in children was based on polymerase chain reaction, HIV-1 p24 antigen tests and HIV antibody tests. Late postnatal transmission was defined as HIV-1 infection occurring after 6 months of age in a child who was uninfected at 6 months of age and who had an HIV-1-seropositive mother. Children born to HIV-seronegative mothers were used as controls. Breast-feeding was universal in this cohort. CD4 and CD8 T lymphocytes were assayed by flow cytometry in the mothers.
  
  
  RESULTS
  Among 139 children born to HIV-1-seropositive mothers and known to be HIV-uninfected at 6 months of age, 8 children became HIV-1-infected at the end of their first year of life or later. No conversions were observed in children younger than 11 months. The 8 conversions were observed during a follow-up covering 1555 child months between 6 and 27 months of age corresponding to a conversion rate of 6.2 per 100 child years. Among 260 children with HIV-seronegative mothers no child became HIV-infected during the follow-up. The percentage of CD4 T lymphocytes was similar in mothers with early and late transmission but was significantly lower in transmitting than in nontransmitting mothers.
  
  
  CONCLUSIONS
  Because no HIV-1 infection occurred in children with HIV-seronegative mothers, we conclude that the observed infections at the end of the first year of life or later among children born to HIV-seropositive women were caused by late transmission from mother to child, most likely through breast-feeding.
authors.affiliation: Swedish Institute for Infectious Disease Control, Karolinska Institute, Stockholm. katarina.karlsson@smi.ki.se
authors.forename: K
authors.initials: K
authors.lastname: Karlsson
authors.forename: A
authors.initials: A
authors.lastname: Massawe
authors.forename: E
authors.initials: E
authors.lastname: Urassa
authors.forename: G
authors.initials: G
authors.lastname: Kawo
authors.forename: G
authors.initials: G
authors.lastname: Msemo
authors.forename: T
authors.initials: T
authors.lastname: Kazimoto
authors.forename: E
authors.initials: E
authors.lastname: Lyamuya
authors.forename: E
authors.initials: E
authors.lastname: Mbena
authors.forename: W
authors.initials: W
authors.lastname: Urassa
authors.forename: U
authors.initials: U
authors.lastname: Bredberg-Råden
authors.forename: F
authors.initials: F
authors.lastname: Mhalu
authors.forename: G
authors.initials: G
authors.lastname: Biberfeld
mesh_terms: D015492:AIDS Serodiagnosis; D001942:Breast Feeding; D018791:CD4 Lymphocyte Count; D002675:Child, Preschool; D005260:Female; D015658:HIV Infections / Q000175:diagnosis / Q000635:transmission*; D006679:HIV Seropositivity; D015497:HIV-1 / Q000302:isolation & purification; D006801:Humans; D007223:Infant; D018445:Infectious Disease Transmission, Vertical; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious; D011446:Prospective Studies; D013636:Tanzania; D013997:Time Factors