Shifting From an Expected to an Opportunistic Pathogen: Characteristics and Trends of Infant Late and Very Late Onset Group B streptococcal (GBS) infection in a Canadian city over a 27-year period

BackgroundDespite decades of study, the characteristics of infants with invasive group B streptococcus (GBS) late onset disease (LOD) (onset day 7 to 89 of life) and in particular very late onset disease (VLOD) (after day 89 of life) are not well described. Materials and MethodsThis was a retrospective cohort study of infants hospitalized in four Edmonton hospitals April 1, 1994 through June 30, 2022 with LOD or VLOD GBS invasive disease. Data were collected on demographics, date of onset of GBS infection, clinical manifestations and outcomes. ResultsThere were 115 episodes of LOD in 111 infants of which 49 (45%) were preterm. Onset was on median day 27 (IQR 19-40.5) of life. All but one infant was bacteremic while 38 (34%) had proven and 17 (15%) had possible GBS meningitis. Five (5%) died before hospital discharge with all deaths presumed to be due to GBS. There were 11 episodes of VLOD in 11 infants (7 [64%] preterm) presenting on median day 116 (IQR 103-138) (range 93-207) of life. Three (27%) had GBS meningitis. All survived to discharge. Infants with VLOD were less likely to be born vaginally and more likely to be mechanically ventilated during their birth hospitalization and have invasive disease with other pathogens than were infants with LOD. Serotype III accounted for 78% of LOD and 64% of VLOD cases. ConclusionGBS remains a significant cause of infant morbidity and mortality. There is increasing evidence that GBS may sometimes be an opportunistic pathogen in infants over 90 days of age.