Fevers in Infants Under 3 Months

This information is useful for children
A baby with a fever rests on a blue blanket.

When your baby spikes a fever, you can't help but worry. A fever—or febrile illness—in infants is something to see a pediatrician about right away because it is the most common sign of childhood illness. 

Since infants with their still-developing immune systems are so vulnerable to infection, most fevers (above 100.4 degrees Fahrenheit) experienced during the first three months of life are taken seriously by pediatricians and emergency medicine doctors alike. 

Illnesses that bring on fevers in infants are usually caused by viral infections, but about 10 percent are caused by potentially more serious bacterial infections, says Paul L. Aronson, MD, a Yale Medicine pediatric emergency specialist. These can include urinary tract infections, blood infections or bacterial meningitis—an infection of the fluid surrounding the brain and spinal cord.

Our experts are actively investigating ways to improve how infants with fevers are treated. Yale New Haven Children's Hospital is joining other hospitals around the country in an effort to determine the best way to treat this age group when they experience a fever.