Microbiology of bacterial orbital cellulitis-tertiary institutional experiences in South Australia: a multi-centre...

This study describes the microbiology of bacterial orbital cellulitis (OC) over an 11-year period and its clinical associations at three tertiary institutions in Adelaide, South Australia.

Multi-centre retrospective study of the microbiology of bacterial OC between January 2012 and August 2022. Pre-septal cellulitis was excluded. Differences in means were determined by the Independent Samples t-test, and categorical data was analysed via Pearson's Chi square. A P-value < 0.05 was statistically significant.

99 patients (male: 69, mean age: 22.0 ± 23.8 years old), of which 70.7% were aged ≤ 18 years. Sinus and orbital abscess cultures had the greatest positive yield (73.7%). Frequency of organisms: Streptococcus species (34.3%), Staphylococcus aureus (28.3%), Haemophilus species (5.1%), mixed anaerobes (3.0%), Enterobacter cloacae (2.0%), Moraxella catarrhalis (1.0%), Pseudomonas aeruginosa (1.0%), Corynebacterium species (1.0%), Klebsiella pneumoniae (1.0%), Proteus mirabilis (1.0%), Citrobacter koseri (1.0%), and Enterococcus species (1.0%). Streptococcus species predominated in the paediatric population, with a statistically significant difference in mean age between Streptococcus species and Staphylococcus aureus (14.1 ± 16.5 vs 27.6 ± 24.6 years old, respectively) (P = 0.028). No organism was cultured in 32.3% of cases. Methicillin-resistant Staphylococcus aureus (MRSA) accounted for 28.6% of all Staphylococcus aureus isolates, with 50% occurring between 2021 and 2022.

Yearly microbiological trends have remained largely constant in South Australia. The causative organism was not identified in 32.3% of cases, further emphasising appropriate empirical antibiotics, and obtaining microbiology from various sources. MRSA OC remains of increased clinical and public health concern and may be associated with a more aggressive disease course.