Blood culture helped detect bacteremia in infants with fever lacking source

Infants aged younger than 3 months presenting to the ED for fever without source should undergo a blood culture to test for bacteremia — especially infants who do not appear well and those with leukocyturia and/or nitrituria, according to study results.

Researchers from Cruces Hospital in Barakaldo, Spain conducted a retrospective, cross-sectional study of infants aged younger than 3 months who presented to the pediatric ED with fever without source from September 2003 to August 2008. They identified 1,125 febrile infants using electronic data from pediatric ED medical records, 91.5% of whom had blood cultures performed.

Cultures from 23 infants produced bacterial pathogens, leading to an overall blood culture–positive rate of 2.2%. The most common pathogens were Escherichia coli and Streptococcus pneumoniae. Urine cultures from eight infants also tested positive for leukocyturia, nitrituria or both. These infants had a higher blood culture–positive rate of 4.4%, according to the researchers.

The results of a multivariate analysis also indicated that general appearance (including abnormalities in respiratory and circulatory functions) and positive outcome on urine dipstick test were predictive for positive blood cultures. However, when evaluated as predictors for positive blood cultures, C-reactive protein, white blood cell count and absolute neutrophil count were deemed unreliable. A CRP value of 70 g/L showed high specificity (93.8%) and negative predictive value (99.3%) but had lower sensitivity (69.6%).

These findings indicated the importance of blood cultures for febrile infants admitted to the ED, but “larger samples are required to establish whether a blood culture should or should not be recommended in the case of selected infants over 1 month old,” the researchers wrote. – by Melissa Foster

Gómez B. Pediatr Infect Dis J. 2010;29:43-47.

The overall rate of bacteremia in this study was 2.2%, which is on par with recent studies in the United States involving infants aged 3 months and younger who had fever. The low number of group B streptococcal bacteremia cases may be related to preventing early-onset disease with effective intrapartum prophylaxis. The number that is most interesting is the 1% rate of bacteremia among infants who did not appear to be ill and whose urine dipstick was normal, which is quite low. Ill-appearing infants had a significantly higher bacteremia rate (12.5%), but I assume that these infants would be admitted and treated empirically with antibiotics. The authors don't define ill-appearing very well. For younger physicians who are unfamiliar with objective studies defining ill-appearance in infants I recommend the publications by my colleague Paul McCarthy published in the 1980s.

The authors describe an observation unit for febrile infants in the second half of their first month of life. In the United States it has been difficult to obtain funding for such a unit, but it appears to be a good idea.

– Robert Batlimore, MD
Infectious Diseases in Children Editorial Board