Microorganisms can reach and infect a fetus or newborn via a number of routes. Vertical spread of a pathogen from an infected mother can occur in utero, during delivery, or postnatally (e.g., ingestion of infected breast milk). Horizontal spread of infectious agents to newborns by means of contaminated hands, stethoscopes, blood products, total parenteral nutrition fluid, or respiratory therapy equipment is well documented and can lead to outbreaks of disease in neonatal intensive care units. Iatrogenic fetal infections occasionally occur after invasive procedures such as fetal scalp monitoring or intrauterine transfusions (1). Infection control in the NICU is discussed in detail in Chapter 49.

Maternal infections acquired shortly before conception or during gestation can adversely affect pregnancy outcome indirectly through nonspecific effects of severe maternal illness (e.g., increased rates of spontaneous abortions, stillbirths, or premature births associated with measles infection during pregnancy) or directly through microbial invasion of the fetus or neonate (2). Pathogens can be transmitted from mothers to their infants through hematogenous spread across the placenta (e.g., cytomegalovirus [CMV], Toxoplasma gondii), ascension from an infected cervix (e.g., herpes simplex virus [HSV]), or intimate contact between a fetus and infected genital secretions during vaginal delivery (e.g., HSV, hepatitis B virus [HBV], human immunodeficiency virus type 1 [HIV-1], papillomaviruses) (3,4,5). Maternal coinfection by other microorganisms may enhance the risk of fetal infection by either or both pathogens (6).

The outcome of a fetal or neonatal infection depends on the stage of pregnancy during which infection occurs, virulence of the pathogen, preexisting maternal immunity to the infecting agent, and efficacy of drug therapy for maternal or neonatal disease. Intrauterine infections may lead to resorption of the embryo, fetal demise resulting in a spontaneous abortion or stillbirth, or delivery of an infected neonate. Infected infants who are asymptomatic at birth may develop chronic problems in late infancy or early childhood (e.g., HIV-1, CMV, hepatitis C virus [HCV]) or during adulthood (e.g., rubella, HBV) (7,8,9,10). Others suffer from severe acute neonatal disease such as pneumonia or hepatitis (e.g., HSV, syphilis), congenital malformations (e.g., CMV, rubella), intrauterine growth retardation, or prematurity (8,10,11). The number of infants born each year with these conditions is substantial (Table 48-1), and the lifetime expenditures for their medical and educational needs are considerable (12,13,14,15,16,17,18,19,20,21,22,23).