pediatrics
Occult Bacteremia and Fever Without Apparent Source in Infants and Young Children
Diagnosis
Blood cultures Urine culture and urinalysis Complete blood count (CBC) and differential Sometimes other tests depending on age and clinical circumstances Diagnosis of bacteremia requires blood cultures; ideally, two samples are taken from separate sites, which helps minimize the problem of false positives due to skin contaminants, and results should be made available within 24 hours. Recommendations for testing and choice of tests vary with age, temperature, and clinical appearance; the goal is to minimize testing without missing an SBI. Children who have indications of focal infection on history or physical examination are evaluated based on those findings. When available, rapid diagnostic tests for Diagnosis , In infants with SBI, the CBC usually shows an elevated white blood cell (WBC) count; however, only about 10% of children with WBC counts of>15,000/mcL (> 15 × 109/L) are bacteremic, so specificity is low. Acute-phase reactants (eg, erythrocyte sedimentation rate, C-reactive protein with or without procalcitonin) are used by some clinicians but add little information; some clinicians believe that elevated procalcitonin levels may be more specific for serious illness. In children<3 months, band counts>1500/mcL (> 1.5 × 109/L) and either low (<5000/mcL [5 × 109/L]) or high (>15,000/mcL [> 15 × 109/L]) WBC counts may indicate bacteremia. It is important to note that any febrile infant, regardless of immunization history, who appears seriously ill or toxic requires complete clinical and laboratory evaluation (CBC with differential, blood cultures, urine cultures, lumbar puncture, and, in most cases, admission to the hospital with empiric antimicrobial therapy). Unimmunized, underimmunized, and immunocompromised febrile infants in this age range are more susceptible to SBI than their peers and also typically require the same full clinical and laboratory evaluation for SBI and empiric antibiotics. Children with dyspnea or low oxygen saturation should also have a chest x-ray. In previously immunized febrile infants aged 3 to 36 months who appear well (nontoxic), the risk of bacteremia is now as low or even lower than the rate of false-positive blood cultures due to skin contaminants, leading many experts to forego blood cultures in these children. However, a urinalysis with microscopic examination and urine culture is typically recommended, but additional laboratory examination (eg, CBC, chest x-ray) is not. Although the vast majority of these children have a viral infection, a very small number of well-appearing children will have an early SBI, so caretakers should be advised to monitor the child's symptoms, give antipyretics, and follow up with the clinician (by visit or telephone depending on the circumstances and the caretakers' reliability) in 24 to 48 hours. Children who worsen or remain febrile should have testing done (eg, CBC with differential, blood cultures, possibly chest x-ray or lumbar puncture). Toxic-appearing or seriously ill-appearing infants require immediate clinical evaluation and collection of blood, urine, and spinal fluid cultures and hospitalization for empiric antibiotic therapy. Unlike in older infants, in those < 3 months of age, a nontoxic clinical appearance does not routinely allow deferral of testing. Algorithms have been developed to help guide evaluation of infants in this age group (for one example, see Figure: Evaluation and management of the febrile infant aged ). In using the algorithm, many experts consider age < 30 days by itself to be a high-risk criterion (and thus routinely admit them and do additional testing), whereas others do not and manage all infants < 90 days of age using the same criteria. This algorithm is sensitive for SBI but relatively nonspecific. Thus, given the relatively low incidence of SBI even among the population of febrile young infants, the algorithm has a high negative predictive value but a low positive predictive value ( see hpf=high-power field. 