Invasive Aggregatibacter infection: shedding light on a rare pathogen in a retrospective cohort analysis


 Introduction. 
 
 
 Aggregatibacter
 
 are Gram-negative, facultatively anaerobic rods or coccobacilli that are infrequently encountered as pathogens causing infection.
 
 Hypothesis/Gap Statement. The range of invasive infection that 
 
 Aggregatibacter
 
 cause is poorly described. The pathogenicity of species such as 
 
 Aggregatibacter segnis
 
 is debated.
 
 Aim. To identify invasive infection due to 
 
 Aggregatibacter
 
 species in a large healthcare organization and to characterize clinical syndromes, co-morbidities and risk factors.
 
 Methodology. All microbiological samples positive for 
 
 Aggregatibacter
 
 species were identified by conventional culture or 16S rRNA PCR between October 2017 and March 2021. Electronic records for all patients with positive samples were reviewed and the infection syndrome classified for patients with invasive disease.
 
 Results. Twenty-seven patients with invasive infection were identified, with a statistically significant difference in species-specific patterns of invasive infection (P=0.02) and a statistically significant association with residence in the 30 % most deprived households in the UK by postcode (P<0.01). The three most common co-morbidities were periodontitis or recent dental work (29.6%), cardiovascular disease (25.9%) and diabetes (18.5 %).
 
 Conclusion. We describe a novel association of 
 
 Aggregatibacter segnis
 
 with skin and soft tissue infection. The propensity of the 
 
 Aggregatibacter
 
 species to cause invasive infection at different body sites and be associated with deprivation is reported. 
 
 Aggregatibacter actinomycetemcomitans
 
 bacteraemia was associated with infective endocarditis, and 
 
 Aggregatibacter aphrophilus
 
 was implicated in severe appendicitis and noted to cause brain abscess. Areas warranting future research include exploring the risk-factors required for invasive infection and those that may determine the species-specific differences in patterns of invasive disease.