INFECTIOUS DISEASE: LIFE-THREATENING INFECTIONS IN
THE INFANT AND CHILD
Infections in the Newborn (also
see Chapter 59
)
The newborn has an increased susceptibility to infection as a
result of a number of developmental immunologic deficiencies. Depressed cell-mediated
immunity renders the fetus and infant more susceptible to viral and fungal infection.
In addition, infants have depressed B-cell function with diminished production of
immunoglobulins. One protective compensatory mechanism is the active transplacental
transfer of maternal immunoglobulin G (IgG), which gives neonates a resonable amount
of IgG at term. At 2 to 3 months of age, however, the level of maternal antibodies
reaches a nadir before the infant adequately assumes antibody production.[332]
This time of relatively low levels of circulating antibody is a period of increased
risk.
A discussion of perinatal infections can be divided into congenitally
acquired and postnatally acquired infections. Congenital infections result from
prenatal exposure to viral, protozoal, or rarely, bacterial pathogens. Common diseases
are the TORCH infections: Toxoplasma gondii (T);
"other" (O), including human immunodeficiency virus (HIV), syphilis, and tuberculosis;
rubella (R); cytomegalovirus (C); and herpes simplex virus type 2 (H). Only rarely
do these infections produce a picture of overwhelming sepsis, but they can sometimes
be confused with bacterial infection when profound CNS depression, circulatory collapse,
or thrombocytopenia are initial signs. When these infections occur in the first
trimester, they can result in fetal wastage or major organ malformation.[333]
The incidence of acute infections in newborns is highest in premature
children. However, regardless of gestational age, the signs and symptoms of infection
are often subtle. Therefore, a very low threshold for diagnosing and treating infection
is important.[334]
Table
76-18
lists the common signs and symptoms of neonatal sepsis.
The most common acquired pathogens are organisms that colonize
the mother's genital tract: group B streptococci, E. coli,
Listeria monocytogenes, and herpesvirus. Herpes
is a particularly fulminant infection in neonates; the presence of active lesions
in the birth canal is an indication for cesarean birth. The most common bacterial
pathogen of sepsis in neonates is group B Streptococcus.
During the immediate perinatal period, infection with
group B streptococci is manifested as severe cardiorespiratory instability and meningitis
(in 30% of cases). In contrast, later manifestation of this pathogen at 2 to 3 weeks
of age is associated with a higher incidence of meningitis and a lower incidence
of pulmonary disease.[335]
Whenever sepsis is suspected, bacterial cultures should be obtained
from blood, urine, and CSF. It is important to perform a complete sepsis workup
because it is difficult for both the infant and the physician to localize an infection.
After appropriate cultures are obtained, broad-spectrum treatment with ampicillin
and an aminoglycoside such as gentamicin is usually begun until specific bacteriologic
information becomes available.
