Invasive Bacterial Infections Other Than Escherichia coli and Streptococcus agalactiae in Febrile Infants Younger Than 90 Days

Background: Invasive bacterial infections (IBIs) in febrile infants ≤90 days are mostly caused by Escherichia coli and Streptococcus agalactiae . However, data on IBIs caused by other pathogens remain limited. Methods: We conducted a multicenter retrospective study of febrile infants aged ≤90 days diagnosed with IBI between 2008 and 2022 at 12 Spanish pediatric emergency departments. Epidemiology, clinical features, microbiology and outcomes of cases caused by pathogens other than E. coli / S. agalactiae were analyzed. Adverse outcomes included death, inotropic or respiratory support, acute complications, or sequelae. Results: Among 375 infants with IBI, 106 (28.3%) had infections caused by pathogens other than E. coli / S. agalactiae . The most frequent pathogens were Staphylococcus aureus (n = 30, 8.0%), Streptococcus pneumoniae (n = 15, 4.0%) and Enterococcus faecalis (n = 14, 3.7%). Most cases presented as isolated bacteremia (65.1%), followed by bacteremic urinary tract infection (18.9%) and meningitis (12.3%); 46.2% of infants with meningitis had a concomitant urinary tract infection. The distribution of pathogens varied according to age, with S. aureus being more frequent among younger infants and S. pneumoniae accounting for 8.6% of IBIs in infants aged 61–90 days. Listeria monocytogenes caused 1.3% of IBIs, with only 1 case identified in the last decade. Adverse outcomes occurred in 7.5% of infants with infections caused by other pathogens and 8.6% of those with E. coli / S. agalactiae (absolute risk difference, −1.0% [95% confidence interval, −7.1 to 5.0]). Conclusions: IBIs caused by pathogens other than E. coli / S. agalactiae accounted for a substantial proportion of cases and showed an age-dependent distribution. Most presented as isolated bacteremia, while meningitis was associated with a higher observed frequency of adverse outcomes.