88 Risk of Serious Bacterial Infections among Recently Immunized Young Febrile Infants in the General Emergency Setting

Abstract

Fever following routine immunizations is a common presenting complaint for young infants in the emergency department (ED). Controversy remains over which well-appearing young febrile infants are at high risk for serious bacterial infection (SBI). The objective of this study was to determine the prevalence of SBI in febrile young infants 6-12 weeks who received immunizations in the preceding 72 hours. The authors conducted a retrospective chart review of infants 6-12 weeks who presented with a fever ≥ 38°C to two military academic emergency departments (ED) over a 4-year period. This study was part of a larger review of febrile infants (between the ages of 0-160 days) investigating rates of SBI and resource utilization pre-and post-implementation of standardized febrile infant clinical pathways. Infants were considered recently immunized (RI) if they had received immunizations within the 72 hours prior to presenting to the ED and not recently immunized (NRI) if they had not received immunizations during this time period. The primary outcome of SBI was based on culture results and final radiology interpretation of chest radiographs. 508 febrile infants were reviewed, of whom 114 had received immunizations (RI) in the prior 72 hours. The overall prevalence of SBI was 11.4% (95% CI = 8.9-14.6) in our study population. The prevalence of SBI in infants not recently immunized (NRI) was 13.7% (95% CI = 10.6-17.6) compared to 3.5% (95% CI = 1.1-9.3) in the infants recently immunized (RI) (see Table 1). The prevalence of SBI in febrile infants who received immunizations within the prior 24 hours was 2% (95% CI = 0.4-7.9) compared to 14.3% (95% CI = 2.5-43.9) in those recently immunized infants who received immunizations greater than 24 hours prior to presentation (see Table 2). The relative risk of SBI in the setting of recent immunizations was 0.3 (95% CI = 0.1-0.7). All but one SBI in the RI group were urinary tract infections (UTI). The single non-UTI was a case of pneumonia in an infant who presented with respiratory symptoms within 24 hours of immunizations. There were no cases of bacteremia or meningitis identified. The prevalence of SBI in febrile young infants presenting within the first 24 hours following immunizations is less compared to those not recently immunized. UTI, however, remains a substantial risk in this population and should be investigated as a potential source of fever. Future research utilizing a large prospective multi-center data registry would aid in further defining the risk of SBI among recently immunized infants.Table 1SBI in Infants with RI and NRIAll (n=508) n % (95% CI)RI (n=114) n (%, 95% CI)NRI (n=394) n (%, 95% CI)Bacteremia3 (0.6%, 0.2-1.9)0 (0%, 0-4)3 (0.8%, 0.2-2.4)UTI47 (9.3%, 6.9-12.2)3 (2.6%, 0.7-8)44 (11.2%, 8.3-14.8)Meningitis1 (0.2%, 0.01-1.3)0 (0%, 0-4)1 (0.3%, 0.1-1.6)Pneumonia6 (1.2%, 0.5-2.7)1 (0.9%, 0.05-5.5)5 (1.3%, 0.5-3.1)Other SBI1 (0.2%, 0.01-1.3)∗0 (0%, 0-4)1 (0.3%, 0.1-1.6)∗Overall SBI58 (11.4%, 8.9-14.6)4 (3.5%, 1.1-9.3)54 (13.7%, 10.6-17.6)∗One infant with salmonella enteritis Open table in a new tab Table 2SBI in Infants with RI Compared to Infants with NRIPrevalence of SBI (95% CI)Relative Risk (95% CI)NRI (n=394)54 (13.7%, 10.6-17.6)Reference groupRI (overall) (n=114)4 (3.5%, 1.1-9.3)0.3 (0.1-0.7)RI <24 hours (n=98)2 (2%, 0.4-7.9)0.2 (0.04-0.6)RI 24-48 (n=14)2 (14.3%, 2.5-43.9)1.04 (0.3-3.9) Open table in a new tab