The Diagnosis and Treatment of Fever in Newborn Infants

A fever in an infant who is less than 28 days old is considerably more concerning than a fever in an older infant. In particular, a fever occurring in the first week of life may represent a life-threatening infection that must be addressed immediately. Fever in a neonate is defined as a rectal temperature of 100.4F or higher.

The infection is usually assumed to be from bacteria obtained while passing through the mother's vagina. One exception to this is viral neonatal infection caused by the Herpes Simplex Virus. Transmission of some infections can occur through the placenta while the baby is in the uterus. These are called TORCH infections and can cause congenital malformations in addition to life-threatening infection. TORCH infections are fortunately uncommon in women with prenatal care. They are also a lengthy topic and are covered in a separate article.

The infectious possibilities in the neonate whose mother received adequate prenatal care include:

1. Pneumonia with onset within 1 to 6 days of life: This is considered to be early onset pneumonia' and is usually caused by Group B Streptococcus or "GBS". Many women are asymptomatic carriers of GBS and are treated with antibiotics just prior to giving birth.

Risk factors for early-onset GBS are:

Rupture of membranes for more than 18 hours before giving birth

Chorioamnionitis or intrapartum temperature higher than 38C

Previous baby with symptomatic GBS infection

Low birth weight baby or prematurity.

2. Pneumonia with onset after 7 days of life is late onset pneumonia' and is usually caused Staphylococcus aureus. Babies in the NICU can also get pneumonia from Pseudomonas.

3. Bacterial sepsis caused by late onset GBS (7-90 days after birth), E. coli, Staphylococcus aureus, or Listeria.

4. Meningitis Caused by GBS, E. coli, Listeria, Herpes Simplex Virus ("HSV"). The risk of neonatal infection with HSV is higher if the mom is first infected during pregnancy (44%) versus moms that have recurrence of their HSV during pregnancy (3%). If the mother is known to have HSV she will be treated with Acyclovir during her pregnancy whether she has visible lesions or not. Only 9% of HSV positive moms have visible sores at the time of delivery!

5. Urinary tract infection Caused by E. coli, Enterococcus, Klebsiella, Proteus. In the neonatal period UTI's are just as common in boys as in girls and can be caused by bacterial entry through the urethra or bacterial seeding from the blood.

A newborn infant can become very sick very fast. Many of the symptoms that allow for differentiation between the above infections in adults are not present in neonates. A one week old infant will not have a stiff neck with meningitis or crackles in their lungs with pneumonia.

The signs of infection in a neonate are:

1. Temperature instability- The baby may become hypothermic or hyperthermic.

2. Tachypnea- Increased respiratory rate with or with out apparent difficulty breathing.

3. Poor feeding- A newborn infant should have a good suck reflex. He or she should breast feed every 2 to 3 hours for 10 to 15 minutes each time.

4. Bradycardia- Slow heart rate.

5. Hypotension- Low blood pressure.

6. Hypoglycemia- Low blood sugar. May manifest as jitteriness or seizures.

When a neonate exhibits signs of infection, it is imperative to discover the source of infection to ensure appropriate medical treatment. A neonate with a fever will automatically require the following tests:

Complete Blood Count

Electrolytes

Blood cultures

Urine analysis

Urine culture

Cerebrospinal Fluid ("CSF") Culture

CSF PCR analysis for HSV

CSF analysis for cell counts, glucose, protein

Some of these tests results can be had within a matter of minutes. However, the cultures of blood, urine and CSF, which help identify the organism causing the infection, can take days to grow. Therefore, newborns are treated empirically without waiting on culture results. This means that they are given antimicrobials that will cover the most common causes of neonatal infection.

Empiric therapy usually includes 14 days of Ampicillin, which covers gram positive bacteria, and Gentamicin, which covers gram negative bacteria. The synergy of this combination of antibiotics is particularly useful for GBS. Another option is Ampicillin and Cefotaxime for 14 days. If the history suggests HSV, then empiric therapy may include Acyclovir for 21 days.

All infants will receive IV fluids, respiratory and nutritional support as necessary. Once the culture results come back, the antibiotic may be changed to narrow the antibiotic coverage toward those specific organisms. If the newborn baby had a urinary tract infection, the baby will need a renal ultrasound to look for urinary tract anomalies.