PC2179: Microbiology and Epidemiology of Orbital Cellulitis in the US Military Health System

Background: Orbital cellulitis is a vision and life-threatening condition impacting both children and young adults. Sinusitis, hematogenous seeding, or direct extension can result in orbital cellulitis which requires management with intravenous antibiotics and frequently surgery. Prior to the widespread use of conjugate vaccines, Haemophilus influenzae type B and pneumococcus were prevalent causes of orbital infections. The microbiology of pediatric infections has shifted in recent years, but data to inform empiric antibiotic decisions are limited to single-center reports. We used the large and diverse US Military Health System (MHS) database to capture epidemiologic and microbiologic trends in pediatric orbital cellulitis to inform future management decisions.

Methods: Using the MHS database, we performed a retrospective analysis of orbital cellulitis infections between June 2009 and September 2019. Cases were identified using discharge ICD9/10 codes. Individuals less than 22 years of age with radiological confirmation of orbital disease were included and we excluded those with ophthalmia neonatorum. Demographic data, co-morbid diagnoses, blood culture and wound culture yields with antibiotic susceptibilities, and antibiotic prescriptions were collected. Results are reported using descriptive statistics and an antibiogram was developed.

Results: 130 cases of radiologically-confirmed orbital cellulitis were identified, which accounted for 14.6 per 100,000 pediatric admissions to US Military Treatment Facilities during the 10-year study period. There was a male predominance (66.9%), and infections were clustered among children ages 2 to 9 years (42.3%) and young adults aged 18 to 21 years (24.6%). Fifty-five percent of cases had a comorbid diagnosis of sinusitis (Table 1). Ninety-seven subjects (75.38%) had at least one blood or wound culture sent and 41 (31.54%) had at least one culture yield a pathogen. Blood cultures had a 3.80% yield and wound cultures 39.74%. The most commonly identified organism was Staphylococcus aureus (18.89%), followed by Streptococcus intermedius (17.78%), and coagulase negative staphylococci (CoNS) (18.89%). H. influenzae and K. pneumoniae were also identified. Of isolates for which susceptibility data was available, 25% of Staphylococcus aureus isolates were methicillin-resistant (MRSA). Clindamycin resistance was identified in 9% of all S. aureus: 33% and 11% of MRSA and MSSA respectively (Figure 1). Additionally, 50% of CoNS and 25% of S. intermedius were resistance to clindamycin (Figure 1). Clindamycin was the most commonly prescribed antibiotic (59.23%), followed by vancomycin (58.46%), and ceftriaxone (53.85%).

Conclusion: Orbital cellulitis occurred infrequently in the MHS and pathogen yields were overall low. However, Staphylococcus aureus was the most frequently identified pathogen with a large percentage being MRSA. Additionally, coagulase negative staphylococci, streptococcal species, and gram-negative pathogens were identified and should be considered in empiric management decisions. Empiric antibiotic selection for these infections should therefore include an anti-MRSA agent plus a broad-spectrum beta-lactam to cover gram negative pathogens.