Causes of Fever in a Neonate
The most common causes of fever in a neonate include serious bacterial infections (particularly urinary tract infections, bacteremia, and meningitis), viral infections, and fungal infections, with bacterial infections requiring the most urgent evaluation and treatment due to their high risk of morbidity and mortality.
Bacterial Causes
Bacterial infections represent the most concerning causes of fever in neonates, with significant risk for rapid progression and adverse outcomes:
Urinary Tract Infections (UTIs)
- Most common serious bacterial infection in febrile neonates 1
- Predominantly caused by Escherichia coli (87.4% of neonatal UTIs) 1
- Higher risk in uncircumcised male infants 1
- May present without typical symptoms or pyuria 2
Bacteremia
- Occurs in approximately 2% of febrile neonates 1
- Common pathogens include:
Bacterial Meningitis
- Occurs in approximately 0.9% of febrile neonates 1
- Causative organisms include:
- Escherichia coli (43.7% of cases) 1
- Group B Streptococcus
- Listeria monocytogenes
- Often presents with nonspecific symptoms rather than classic meningeal signs 1
Pneumonia
- Common bacterial cause of fever in neonates 1
- May present with respiratory distress, poor feeding, or irritability
- Often lacks typical respiratory symptoms in neonates 1
Viral Causes
Viral infections are actually more common than bacterial infections in febrile neonates, though often less immediately life-threatening:
Enteroviruses
- Most common viral pathogens in febrile neonates (35% of cases) 2
- Can cause aseptic meningitis, which is the most frequent diagnosis among viral infections 2
- Seasonal peaks in summer and fall
Respiratory Viruses
- Respiratory syncytial virus (RSV) - second most common viral pathogen in NICUs 3
- Influenza viruses
- Parainfluenza viruses
- Adenoviruses (9.38% of viral outbreaks in NICUs) 3
Gastrointestinal Viruses
- Rotavirus (23.44% of viral outbreaks in NICUs) 3
- Norovirus
- May present with or without diarrhea
Herpes Simplex Virus (HSV)
- Less common but potentially devastating infection 1
- Can cause encephalitis, disseminated disease, or skin/mucous membrane disease
- High mortality and neurological morbidity if untreated
Fungal Causes
Fungal infections are less common but significant, especially in premature or hospitalized neonates:
Invasive Candidiasis
- Risk factors include prematurity, central venous catheters, parenteral nutrition, and prior antibiotic use 4
- Associated with high morbidity and mortality 1
- May present with nonspecific signs similar to bacterial sepsis 1
Clinical Presentation
Neonates with fever often present with nonspecific symptoms:
- Fever (rectal temperature ≥38.0°C/100.4°F) 1
- Irritability or lethargy
- Poor feeding
- Respiratory distress (particularly common in Group B streptococcal infections) 1
- Hypothermia (rather than fever in some cases) 1
- Skin changes (including petechiae, purpura, or rash)
- Seizures (9-34% of cases, more common with GBS meningitis) 1
Important Considerations
Absence of fever doesn't rule out infection: Neonates may have serious infections while being hypothermic or normothermic 1
Nonspecific presentation: Classic signs of infection are often absent in neonates 1
Multiple infections: Bacterial and viral infections can coexist 1
Risk stratification: No single clinical prediction rule for identifying neonates with serious bacterial infection has been universally accepted 1
Recent antipyretic use: May mask fever at presentation 1
Home temperature measurement: Consider accuracy of home temperature measurement devices 1
History of fever: Neonates presenting afebrile with history of fever who remain afebrile during observation may have lower odds of serious bacterial infection 5
The evaluation of fever in a neonate requires a comprehensive approach with a low threshold for performing a full sepsis workup, as the risk of serious bacterial infection is significant and the presentation is often subtle or nonspecific.