Background : An outbreak of chikungunya virus affected over one-third of the population of La ReÃ?´union\nIsland between March 2005 and December 2006. In June 2005, we identified the first case of\nmother-to-child chikungunya virus transmission at the Groupe Hospitalier Sud-ReÃ?´union level-3\nmaternity department. The goal of this prospective study was to characterize the\nepidemiological, clinical, biological, and radiological features and outcomes of all the cases\nof vertically transmitted chikungunya infections recorded at our institution during this\noutbreak.\nMethods and Findings : Over 22 mo, 7,504 women delivered 7,629 viable neonates; 678 (9.0%) of these parturient\nwomen were infected (positive RT-PCR or IgM serology) during antepartum, and 61 (0.8%) in\npre- or intrapartum. With the exception of three early fetal deaths, vertical transmission was\nexclusively observed in near-term deliveries (median duration of gestation: 38 wk, range 35ââ?¬â??40\nwk) in the context of intrapartum viremia (19 cases of vertical transmission out of 39 women\nwith intrapartum viremia, prevalence rate 0.25%, vertical transmission rate 48.7%). Cesarean\nsection had no protective effect on transmission. All infected neonates were asymptomatic at\nbirth, and median onset of neonatal disease was 4 d (range 3ââ?¬â??7 d). Pain, prostration, and fever\nwere present in 100% of cases and thrombocytopenia in 89%. Severe illness was observed in\nten cases (52.6%) and mainly consisted of encephalopathy (nÃ?¼9; 90%). These nine children had\npathologic MRI findings (brain swelling, n Ã?¼ 9; cerebral hemorrhages, n Ã?¼ 2), and four evolved\ntowards persistent disabilities.\nConclusions: Mother-to-child chikungunya virus transmission is frequent in the context of intrapartum\nmaternal viremia, and often leads to severe neonatal infection. Chikungunya represents a\nsubstantial risk for neonates born to viremic parturients that should be taken into account by\nclinicians and public health authorities in the event of a chikungunya outbreak.
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