Fever in the first six months of life: risks of underlying serious infection.

The age-specific rate of elevated temperature over 37.8 C was evaluated in all infants less than 6 months of age (n = 1341) seen from July 1, 1974 to June 30, 1978 in a family practice clinic. Mild elevations (37.8 C-38.3 C) were common even in the first few months of life, and accounted for 20.7 per cent of infant visits. Temperatures greater than 38.3 C are uncommon in the first months of life but are seen more frequently with each succeeding month. Temperature elevation over 38.3 C was associated with a significantly higher rate of meningitis (p less than .01), otitis media (p less than .001) and lower respiratory infection (p less than .05). Significantly higher laboratory usage was documented in infants less than 3 months and for infants with temperature more than 38.3 C. The high rate of mild temperature elevations in young infants suggests that a selective diagnostic strategy directed at high-risk infants is important. Infants less than three months of age with a fever exceeding 38.3 C are calculated to have 21.5 times the risk of a serious underlying infection as infants older than three months with a similar temperature elevation. Clinical evaluation must remain an important tool in determining which febrile infants should be evaluated by further laboratory and diagnostic tests.