From the Guidelines
A fever in a 4-month-old baby is generally considered to be a rectal temperature of 100.4°F (38°C) or higher, as defined in the clinical setting or at home within the past 24 hours 1. When evaluating a 4-month-old with a fever, it is essential to consider the potential risks of serious bacterial infections (SBI), which can be devastating in this age group. According to the study by 1, the risk of SBI in febrile infants aged 90 days or younger is approximately 7%.
Key Considerations
- Rectal temperatures provide the most accurate readings for infants, and a temperature of 100.4°F (38°C) or higher is considered a fever 1.
- If using other methods, an axillary (armpit) temperature of 99°F (37.2°C) or higher, or a temporal artery or ear temperature of 100.4°F (38°C) or higher would indicate a fever.
- For a 4-month-old with a fever, contact your pediatrician promptly as infants this young need medical evaluation when febrile.
- While waiting for medical advice, you can give acetaminophen (Tylenol) at a dose of 10-15 mg per kg of body weight every 4-6 hours to help reduce the fever, but never give aspirin or ibuprofen (Motrin, Advil) to infants under 6 months.
Management and Prevention
- Keep your baby hydrated with breast milk or formula and dress them in light clothing.
- Fevers in young infants are concerning because their immune systems are still developing, making them more vulnerable to serious infections, and they cannot communicate their symptoms effectively.
- Always use a reliable thermometer and take the temperature correctly for accurate readings. It is crucial to prioritize the health and well-being of the infant, and any concerns about fever or potential SBI should be addressed promptly by a pediatrician 1.
From the Research
Definition of Fever in Infants
- A fever in infants is defined as a rectal temperature greater than 38.0 degrees C (>100.4 degrees F) 2
Age-Specific Considerations
- For infants younger than 28 days, a fever requires a "full sepsis workup" and admission for parenteral antibiotic therapy 2
- For infants aged 1 to 4 months, clinical and laboratory criteria can be used to identify a low-risk population 2
Fever Management
- A recently documented fever at home should be considered the same as a fever in the emergency department (ED) and managed similarly 2
- Acetaminophen can be used to treat fever, but its effects on the underlying infection are unknown 3, 4