Respiratory infections due to a virus, such as colds or flu Gastroenteritis (infection of the digestive tract) due to a virus Certain bacterial infections, particularly ear infections (otitis media), sinus infections, pneumonia, and urinary tract infections Newborns and young infants are at higher risk of certain serious infections because their immune system is not fully developed. Such infections may be acquired before birth or during birth and include sepsis (a serious infection of the blood), pneumonia (infection of the small air sacs of the lungs), and meningitis (infection of the tissues covering the brain). Children under 3 years old who develop a fever (particularly if their temperature is 102.2° F [39° C] or higher) sometimes have bacteria in their bloodstream (bacteremia). Unlike older children, they sometimes have bacteremia with no symptoms besides fever (called occult bacteremia). Routine vaccines against the bacteria that usually cause occult bacteremia (Streptococcus pneumoniae and Haemophilus influenzae type b [Hib]) are now widely used in the United States and Europe. As a result, these vaccines have nearly eliminated occult bacteremia in children in this age group. Less common causes of acute fevers include side effects of vaccinations and of certain drugs, bacterial infections of the skin (cellulitis) or joints (septic arthritis), encephalitis, and viral or bacterial infections of the brain (Kawasaki disease), the tissues covering the brain (meningitis), or both. Heatstroke causes a very high body temperature. Typically, a fever due to vaccination lasts a few hours to a day after the vaccine is given. However, some vaccinations can cause a fever even 1 or 2 weeks after the vaccine is given (as with measles vaccination). Children who have a fever when they are scheduled to receive a vaccine can still receive the vaccine. Chronic fever Chronic fever most commonly results from A prolonged viral illness Back-to-back viral illnesses, especially in young children Chronic fever can also be caused by many other infectious and noninfectious disorders. Infectious causes of chronic fever include Hepatitis Sinusitis Pneumonia Abdominal abscesses (pockets of pus in the abdomen) Infections of the digestive tract caused by bacteria or parasites Bone infections (such as osteomyelitis) Heart infections (such as endocarditis) Tuberculosis Noninfectious causes of chronic fever include Inflammatory bowel disease Juvenile idiopathic arthritis or other connective tissue disorders some times teething also causes fever and chills