Fever without apparent source on clinical examination

PURPOSE OF REVIEW: Routine immunization of children with the heptavalent pneumococcal conjugate (PCV7) vaccine and rapid tests for identification of viruses since the last review in 2002 make this review timely and relevant. RECENT FINDINGS: Since the introduction of the PCV7 vaccine, the incidence of true bacteremia has decreased to 1% and has impacted the epidemiology of fever in the under-3-year-old population, making urinary tract infection the most common cause. Polymerase chain reaction testing for viruses helps in early diagnosis and serves to decrease the unnecessary use of antibiotics. Serious infections are dependent not only on the virulence of the agent, but also on host susceptibility, which has been getting more attention recently. Kawasaki disease in the very young infant is also discussed and awareness is increasing among physicians. SUMMARY: The decrease in the rate of bacteremia since the PCV7 vaccine was introduced means that the management guidelines for fever in the under-3-year-old population need to be reviewed. In addition, better markers are required to predict serious bacterial infection in this population. Further research into the understanding of the host immune response is also needed.