What is fever? Normal temperature in infants less than 3 months old

Area of Science:

• Pediatrics
• Neonatology
• Public Health

Background:

• Establishing a precise definition of fever in infants is crucial for timely medical intervention.
• Current fever definitions may lead to over- or under-diagnosis in well-infant populations.
• Infant body temperature can be influenced by age, season, and measurement method.

Purpose of the Study:

• To determine the normal rectal temperature range in healthy infants younger than three months.
• To evaluate the current definition of fever (> or = 38.0°C) in this age group.
• To propose age-specific fever thresholds for infants.

Main Methods:

• Rectal temperatures were measured in 691 healthy infants (<3 months) during well-baby visits using electronic thermometers.
• Statistical analysis included calculating the mean, standard deviations, and percentiles.
• Temperature variations were analyzed based on infant age (in days/months) and season.

Main Results:

• The mean rectal temperature was 37.5°C ± 0.3°C.
• A temperature of > or = 38.1°C was two standard deviations above the mean.
• Fever definitions varied by age: > or = 38.0°C (0-30 days), > or = 38.1°C (31-60 days), > or = 38.2°C (61-91 days).
• Temperatures were higher in summer than winter.

Conclusions:

• A single fever cutoff of > or = 38.0°C misclassifies approximately 6.5% of well infants.
• Age-specific fever definitions are recommended for infants under three months.
• These findings support refined fever guidelines for early infant care.