Infections of the Fetus and Newborn

The far-reaching impact of microbes on the human condition cannot be overestimated. The microbial species are vast, diverse, and present in virtually every ecosystem on earth. A single gram of human feces, for example, is estimated to contain 10¹¹bacteria, which is equivalent to 10–50% of all the human cells in the body, and is nearly two orders of magnitude higher than the total number of people on the planet. Humans have therefore evolved elaborate and elegant defense mechanisms to maintain health in a microbe-rich environment. Nowhere are these mechanisms more important for the overall health of the species than in pregnancy and childbirth, and in the vast majority of cases, host defense mechanisms provide for healthy infants. A very small subset of microbes have developed ways to subvert host defense and cause infections in pregnancy or the perinatal period that are damaging to the fetus and/or infant, and these infections cause substantial morbidity and mortality throughout the...