Although at least 100 different Escherichia coli capsular antigens have been recognised, strains possessing the K1 antigen are responsible for 77% of neonatal E. coli meningitis cases. K1 strains were found in 20-40% of rectal swab cultures from healthy infants, children, and adult women. Vertical transmission from mother to infant was the most common means of acquiring K1 organisms in term infants. Premature babies in a nursery with little maternal contact acquired K1 strains later than did term infants, and this acquisition may have been related to carriage by nursery staff. Capsular content and fermentation reactions of cerebrospinal-fluid K1 organisms were comparable to those found in rectal strains from healthy individuals. E. coli K1 with identical O and H antigens were found in maternal and infantile cultures of babies with E. colimeningitis. It seems very likely that host immune mechanisms play a significant role in the pathogenesis of neonatal E. coli K1 meningitis.
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