Fetal and neonatal infections can be acquired via varying routes during different stages of pregnancy and birth:
Prenatal: Infection can be transmitted transplacentally or, if there is prelabor rupture of the amniotic membranes, as an ascending infection from the lower genital tract (prenatal).
Intrapartum: During the first stage of labor (or in cases of prelabor rupture of membranes), infection may be transmitted to the fetus while still in utero, via ascending infection from the lower genital tract (vulva, vagina, or cervix). During the second stage of labor, infection may be transmitted through direct contact of the fetus with maternal vaginal fluid or blood.
Postpartum: Neonates may acquire infection through any potential route (eg, bloodborne, droplets).
Common viruses that can cause fetal or neonatal infections include herpes simplex viruses, HIV, cytomegalovirus (CMV), and hepatitis B. Intrapartum infection with HIV or hepatitis B occurs from direct contact with virus in vaginal fluid or by ascending infection from the lower genital tract (vulva, vagina, cervix) if delivery is delayed after rupture of membranes; these viruses can less commonly be transmitted transplacentally. CMV is commonly transmitted transplacentally.
Common bacteria include group B streptococci, enteric gram-negative organisms (primarily Escherichia coli), Listeria monocytogenes, gonococci, syphilis, and Chlamydia trachomatis.
Prenatal (in utero) infection
In utero infection, which can occur any time before birth, results from overt or subclinical maternal infection. Potential consequences depend on the organism and timing of infection in gestation and include spontaneous abortion, intrauterine growth restriction, preterm birth, stillbirth, congenital malformation (eg, rubella), and symptomatic (eg, CMV, toxoplasmosis, syphilis) or asymptomatic (eg, CMV) neonatal infection.
Common infections transmitted transplacentally include rubella, toxoplasma, CMV, syphilis, and Zika virus. HIV and hepatitis B are less commonly transmitted transplacentally.
Intrapartum infection
Intrapartum infections occur during the labor and delivery process. Neonatal infections with herpes simplex viruses, HIV, hepatitis B, group B streptococci, enteric gram-negative organisms (primarily Escherichia coli), Listeria monocytogenes, gonococci, and chlamydiae usually occur from contact with infected vaginal blood or fluid. Sometimes ascending infection can occur during the first stage of labor while the fetus is still in utero (before the cervix is fully dilated and fetal descent), particularly if delivery is delayed after rupture of membranes.
Postpartum infection
Postpartum infections are acquired after delivery through direct contact with infected maternal tissue or bodily fluids (eg, tuberculosis, which also is sometimes transmitted in utero), through breastfeeding (eg, HIV, CMV), or through contact with family or visitors, health care professionals, or the hospital environment (numerous organisms—see Neonatal Hospital-Acquired Infection).
Risk factors for neonatal infection
The risk of contracting intrapartum and postpartum infection is inversely proportional to gestational age. Neonates are immunologically immature, with decreased cell-mediated immune function; preterm infants are particularly so (see also Neonatal Immunologic Function).
Maternal IgG antibodies are actively transported across the placenta, but effective levels for all organisms are not achieved until near term. IgM antibodies do not cross the placenta. Preterm infants have decreased intrinsic antibody production and reduced complement activity. Preterm infants are also more likely to be exposed to corticosteroids and invasive procedures (eg, endotracheal intubation, prolonged IV access) that may predispose to infection.
Symptoms and Signs of Neonatal Infections
Symptoms and signs of infection in neonates tend to be nonspecific (eg, vomiting or poor feeding, increased sleepiness or lethargy, fever or hypothermia, tachypnea, rashes, diarrhea, abdominal distention).
Many infections acquired before birth can cause or be accompanied by various abnormalities of growth or development (eg, growth restriction, deafness, microcephaly, anomalies, growth and weight faltering [formerly failure to thrive], hepatosplenomegaly, neurologic abnormalities).
Diagnosis of Neonatal Infections
History and physical examination
Microbiology, blood count, inflammatory markers
A wide variety of infections, including sepsis, should be considered in neonates who are ill at or shortly after birth, particularly those with risk factors. Infections such as congenital rubella, syphilis, toxoplasmosis, and CMV should be considered in neonates with abnormalities such as growth restriction, deafness, microcephaly or other physical anomalies, hepatosplenomegaly, or neurologic abnormalities.
Initial laboratory tests can include a complete blood count with differential and inflammatory markers (eg, C-reactive protein or procalcitonin). Specific microbiology tests (eg, culture, nucleic acid amplification) can confirm the causative organism. Maternal testing may also be helpful.
Treatment of Neonatal Infections
Antimicrobial therapy
Supportive care
The primary treatment for presumed bacterial infection in the neonate is prompt empiric antimicrobial therapy with medications such as ampicillin and gentamicin or ampicillin and cefotaxime. Final antimicrobial selection is based on culture results similar to the practice in adults, because infecting organisms and their sensitivities are not specific to neonates. However, medication dose and frequency are affected by numerous factors, including age and weight. In cases of suspected viral infection, or a history of pre- or perinatal exposure to viruses, appropriate antiviral therapy may be indicated (eg post-exposure prophylaxis for HIV, acyclovir for suspected HSV disease or exposure)The primary treatment for presumed bacterial infection in the neonate is prompt empiric antimicrobial therapy with medications such as ampicillin and gentamicin or ampicillin and cefotaxime. Final antimicrobial selection is based on culture results similar to the practice in adults, because infecting organisms and their sensitivities are not specific to neonates. However, medication dose and frequency are affected by numerous factors, including age and weight. In cases of suspected viral infection, or a history of pre- or perinatal exposure to viruses, appropriate antiviral therapy may be indicated (eg post-exposure prophylaxis for HIV, acyclovir for suspected HSV disease or exposure)
Supportive care may be necessary, particularly in neonates with fever, significant metabolic derangement, respiratory distress/respiratory failure, or septic shock.
