Fever is the most common presenting complaint of infants and children presenting to an emergency department. Fever accounts for 15 percent of all ED visits for pediatric patients younger than 15 years of age. Very young patients, particularly those younger than 3 months of age, have a somewhat immature immune system, which makes them more susceptible to infections. Most infants and children with a fever will have a benign, self-limited infection. However, a few of these febrile infants and children may have a serious, even life-threatening infection. The toxic or ill-appearing infant or child usually does not pose a diagnostic dilemma. However, not all infants and young children with a serious, life-threatening infection will appear ill or toxic. The dilemma for the health care provider is to differentiate the well-appearing febrile infant or child with a serious bacterial infection from the febrile infant or child with a benign, usually viral infection.

Fever accounts for 15 percent of all ED visits for pediatric patients younger than 15 years of age. Very young patients, particularly those younger than 3 months of age, have a somewhat immature immune system, which makes them more susceptible to infections.

In the years following the introduction of the pneumococcal vaccine and the Haemophilus influenza type b vaccines, there have been changes in the predominant bacterial pathogens and in the incidences of the various types of serious bacterial infections. The incidences of occult bacteremia, pneumococcal meningitis, and pneumococcal pneumonia have declined, while Escherichia coli has become the predominant bacterial pathogen and the leading cause of bacteremia, urinary tract infections, and bacterial meningitis in young infants. The most common serious bacterial infection is now urinary tract infection in febrile infants younger than 24 months of age, with a prevalence of 5 percent to 7 percent and higher in certain high-risk groups (eg, up to 20 percent in uncircumcised male infants). Various diagnostic technologies, including rapid antigen testing for viruses and bacteria, have been produced.

Multiple clinical decision rules have been proposed and various biological markers suggested for use in the identification of serious bacterial infection, including the white blood cell count, absolute neutrophil count, band count, C-reactive protein, interleukins, and procalcitonin. However, at present, there is no widespread acceptance of any one clinical decision rule or screening test,

Future research should focus on the changing epidemiology of serious bacterial infections, the use of diagnostic technologies, and the utility of specific biomarkers and clinical algorithms in the differentiation of infants and children with benign febrile illness from febrile infants and children with a serious bacterial infection.