Neonatal Infections

The incidence of infection in the fetus and newborn infant is high. As many as 2% of fetuses are infected in utero and up to 10% of infants are infected during delivery or in the first few months of life. The predominant microorganisms known to cause these infections are cytomegalovirus, herpes simplex virus, rubella virus, Toxoplasma gondii, Treponema pallidum, Chlamydia, Group B Streptococcus, Enterococcus spp., Escherichia coli, and anaerobic bacteria. All of these agents can colonize or infect the mother and infect the fetus or newborn either intrauterinely or during the passage through the birth canal. Although anaerobic bacteria cause a small number of these infections, the conditions predisposing to anaerobic infections in newborns are similar to those associated with aerobic microorganisms. Furthermore, the true incidence of anaerobic infections may be underestimated because techniques for the recovery and isolation of anaerobic bacteria are rarely used, or are inadequate. Several factors have been associated with acquisition of local or systemic infection in the newborn. Most of these factors are vague and difficult to define; however, most studies have described the presence of one or more risk factors in the pregnancy and delivery of these infants: premature and prolonged rupture of membranes (longer than 24 hours), maternal peripartum infection, premature delivery, low birth weight, depressed respiratory function of the infant at birth or fetal anoxia, and septic or traumatic delivery (1-3).

Maternal infection at the time of delivery, can be associated with the development of infection in the newborn. Transplacental hematogenous infection that can spread before or during delivery is another way in which the infant can be infected (4). The acquisition of infection while the newborn passes through the birth canal is, however, the most frequent mode of transfer.

During pregnancy, the fetus is shielded from the flora of the mother's genital tract. Potentially pathogenic bacteria are found in the amniotic fluid (AF) even when the membranes are intact. Prevedourakis et al. (5) documented bacterial invasion of the intact amnion in nearly 8% of the pregnant women in their sample, but this was of no consequence to the mother or the newborn infant. It was suspected that the AF may have antibacterial properties, probably owing to lack of nutritional factors (5,6). The AF actively inhibited the growth of aerobic bacteria, through a phosphate-sensitive cationic protein that is regulated by zinc (7). Its activity was independent of the muramidase and peroxidases, and spermine. The pH of the AF is the only variable predictive of bacterial growth in AF in a laboratory model (8).

The antimicrobial properties of the AF also vary with the period of gestation; it is the least inhibitory against E. coli and Bacteroides fragilis during the first trimester and most inhibitory during the third trimester (8,9). The relative scarsity of the B. fragilis population in the cervix at term labor and the added inhibitory effect of the AF at term may together explain the relatively low incidence of B. fragilis infections at full term as compared to postabortal sepsis (10-12).

Following the rupture of the membranes, the colonization of the newborn is initiated (4) by further exposure to the flora during the infant's passage through the birth canal. When premature rupture of the membranes occurs, the ascending flora can cause infection of the AF with involvement of the fetal membranes, placenta, and umbilical cord (13). Aspiration of the infected AF can cause aspiration pneumonia. Since anaerobic bacteria are the predominant organisms in the mother's genital flora (14), they become major pathogens in infections that follow early exposure of the newborn to that flora.

Genetic factors may be responsible for the predominance of sepsis in the newborn male (15). The immaturity of the immunologic system, which is manifested by decreased function of the phagocytes and decreased inflammatory reactions, may also contribute to the susceptibility of infants to microbial infection (16,17). The presence of anoxia and acidosis in the newborn may interfere also with the defense mechanisms.

The support systems and procedures used in regular nurseries and intensive care units can facilitate the acquisition of infections. Offending instruments include umbilical catheters, arterial lines, and intubation devices. Contamination of equipment such as humidifiers and supplies such as intravenous solutions and infant formulas, and poor isolation techniques can result in outbreaks of bacterial or viral infections in nurseries. Such spread is thought to contribute to clustering of cases of necrotizing enterocolitis in newborns.

Pregnancy And Childbirth

Pregnancy And Childbirth

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