Bacterial sepsis and meningitis often are linked closely in neonates. Despite this association, the incidence of meningitis relative to neonatal sepsis has been on a steady decline. The incidence of meningitis is approximately 1 in 20 cases of sepsis. The causative organisms isolated most frequently are the same as for neonatal sepsis: group B streptococci, E. coli, and
L. monocytogenes. Gram-negative organisms, such as Klebsiella, Salmonella, and Serratia marcescens, are more common in less developed countries, and coagulase-negative staphylococcus needs to be considered in very low birth weight infants. Male infants seem to be more susceptible to neonatal infection than female infants. Severely premature infants are at even greater risk secondary to less effective defense mechanisms and deficient transfer of antibodies from the mother to the fetus (which occurs mostly after 32 weeks’ gestation). Neonates in the neonatal intensive care unit live in a hostile environment, with exposure to endotracheal tubes, central arterial and venous catheters, and blood draws, all predisposing to bacteremia and meningitis. Genetic factors have been implicated in the ability of bacteria to cross the blood-brain barrier. This penetration has been noted for group B streptococci, E. coli, Listeria, Citrobacter, and Streptococcus pneumoniae.
Neonatal sepsis presents during three periods. Early-onset sepsis often begins in utero and usually is a result of infection caused by the bacteria in the mother’s genitourinary tract. Organisms related to this sepsis include group B streptococci, E. coli, Klebsiella, L. monocytogenes, and nontypeable
H. influenzae. Most infected infants are premature and show nonspecific cardiorespiratory signs, such as grunting, tachypnea, and cyanosis at birth. Risk factors for early-onset sepsis include vaginal colonization with group B streptococci, prolonged rupture of the membranes (>24 hours), amnionitis, maternal fever or leukocytosis, fetal tachycardia, and preterm birth. African American race and male sex are unexplained additional risk factors for neonatal sepsis.
Early-onset sepsis (birth to 7 days) is an overwhelming multiorgan system disease frequently manifested as respiratory failure, shock, meningitis (in 30% of cases), disseminated intravascular coagulation, acute tubular necrosis, and symmetrical peripheral gangrene. Early manifestations—grunting, poor feeding, pallor, apnea, lethargy, hypothermia, or an abnormal cry—may be nonspecific. Profound neutropenia, hypoxia, and hypotension may be refractory to treatment with broad-spectrum antibiotics, mechanical ventilation, and vasopressors such as dopamine and dobutamine. In the initial stages of early-onset septicemia in a preterm infant, it is often difficult to differentiate sepsis from respiratory distress syndrome. Because of this difficulty, premature infants with respiratory distress syndrome receive broad-spectrum antibiotics.