Most Common Pathogen in ABRS
Streptococcus pneumoniae is the most common bacterial pathogen in acute bacterial rhinosinusitis (ABRS), accounting for approximately 30-41% of cases in adults and 25-30% in children. 1
Primary Bacterial Pathogens
The three dominant pathogens isolated from maxillary sinus aspirates in ABRS are:
- Streptococcus pneumoniae: 30-41% in adults, 25-30% in children 1
- Haemophilus influenzae (nontypeable): 29-35% in adults, 15-20% in children 1
- Moraxella catarrhalis: 4-8% in adults, 15-20% in children (more common in pediatric populations) 1
Age-Related Differences
Moraxella catarrhalis shows significantly higher prevalence in children compared to adults, making it the third most common pathogen in pediatric ABRS. 1 This age-related distribution is critical when selecting empiric antibiotic therapy, as M. catarrhalis produces beta-lactamases in essentially 100% of isolates. 1
Less Common Pathogens
- Other streptococcal species, anaerobic bacteria, and Staphylococcus aureus cause only a small percentage of ABRS cases 1
- Staphylococcus aureus is rarely isolated from sinus aspirates in uncomplicated ABRS, though it becomes significant in orbital and intracranial complications 1
- Sterile aspirates occur in 20-35% of cases, indicating viral or non-bacterial etiology 1
Clinical Resistance Patterns
Understanding resistance is essential for treatment selection:
- 15% of S. pneumoniae are penicillin-intermediate and 25% are penicillin-resistant in recent U.S. studies 1
- Approximately 30% of H. influenzae produce beta-lactamase, rendering them resistant to amoxicillin 1
- Essentially all M. catarrhalis isolates (>90%) produce beta-lactamases 1
- Macrolide resistance in S. pneumoniae exceeds 40% in the United States 1
Common Pitfalls to Avoid
- Do not assume nasal discharge color indicates bacterial infection—purulent discharge alone does not distinguish bacterial from viral rhinosinusitis 1
- Avoid obtaining nasopharyngeal cultures to predict sinus pathogens, as they are neither sensitive nor specific compared to direct sinus aspirates 2
- Do not overlook recent antibiotic exposure (within 4-6 weeks), which is a major risk factor for antimicrobial-resistant strains and should guide empiric therapy selection 1
- Recognize that imaging (CT, plain films) is not necessary for diagnosing uncomplicated ABRS 1
- Remember that maxillary sinus aspiration is the gold standard for microbiologic diagnosis, though rarely performed in routine practice; middle meatus cultures have not been validated against aspirates in children with ABRS 1