Objective: To evaluate potential markers of serious bacterial infection (SBI) in infants under 3 months of age presenting with fever of unknown origin.
Material and methods: We retrospectively studied all infants under 3 months of age seen in the emergency department between January 2004 and December 2006 for a febrile syndrome with no identifiable focus. Clinical data, procalcitonin (PCT), C reactive protein (CRP) and leucocyte count were evaluated for their ability to discriminate between SBI and non SBI; receiver operating characteristic (ROC) curves were constructed for the laboratory markers and analysis was performed by multivariate logistic regression.
Results: The sample comprised 347 patients (23.63% with SBI). Mean PCT, CRP, leucocyte and neutrophil count were significantly higher in the group with SBI unlike the other criteria studied. The area under the ROC curve (AUC) for PCT was 0.77 (95% confidence interval (CI) 0.72-0.81) and 0.79 for CRP (95% CI 0.75-0.84); both these variables were stronger predictors than leucocyte count (0.67, 95% CI 0.63-0.73). In the 15 infants with more invasive bacterial infections (sepsis, bacteraemia, bacterial meningitis), the diagnostic value of PCT (AUC 0.84, 95% CI 0.79-0.88) was higher than CRP (AUC 0.68, 95% CI 0.63-0.73). In infants who had been febrile for under 12 hours, the differences between PCT, CRP and leucocyte count were statistically significant in both SBI and non-SBI groups, with increasing predictive value of PCT and decreasing value of CRP.
Conclusions: PCT, CRP, and leucocyte count have intrinsic predictive value for SBI in febrile infants under 3 months of age. The diagnostic value of PCT is greater than CRP for more invasive bacterial infections and for fever of short duration.