Bacterial infection of paranasal sinuses lasting <4 weeks, typically following viral URI.
Also known as: acute bacterial sinusitis, ABRS, acute rhinosinusitis, sinus infection
Overview
Acute bacterial rhinosinusitis (ABRS) is symptomatic inflammation of the paranasal sinuses lasting <4 weeks, distinguished from viral rhinosinusitis by duration ≥10 days without improvement, worsening after initial improvement ('double-sickening'), or severe onset with high fever and purulent discharge ≥3-4 consecutive days.
Epidemiology
Acute rhinosinusitis affects ~12% of US adults annually. Only 0.5-2% of viral rhinosinusitis cases progress to ABRS, yet antibiotics are over-prescribed. Maxillary sinus most commonly affected, followed by ethmoid, frontal, then sphenoid.
Try two board-style Acute Bacterial Rhinosinusitis questions
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Question 1EENTMedium
A 34-year-old woman presents with 12 days of right-sided facial pressure, nasal congestion, and thick yellow-green nasal discharge. She had a runny nose and sore throat 2 weeks ago that had nearly resolved before her symptoms worsened over the past several days. Temperature is 38.6°C (101.5°F). Anterior rhinoscopy shows edematous, erythematous nasal mucosa with purulent discharge in the right middle meatus, and there is tenderness over the right maxillary sinus. A diagnosis of acute bacterial rhinosinusitis is made. Which of the following best explains the findings?
AOstial obstruction with impaired mucociliary clearance
BHematogenous bacterial seeding of the sinus mucosa
CAutoimmune granulomatous destruction of nasal cartilage
DIgE-mediated mast cell degranulation of nasal mucosa
ECongenital dynein arm defect causing ciliary dysmotility
Reveal answer & full explanation
Correct answer: A — Ostial obstruction with impaired mucociliary clearance
AOstial obstruction with impaired mucociliary clearance✓
BHematogenous bacterial seeding of the sinus mucosa
CAutoimmune granulomatous destruction of nasal cartilage
DIgE-mediated mast cell degranulation of nasal mucosa
ECongenital dynein arm defect causing ciliary dysmotility
Why Ostial obstruction with impaired mucociliary clearance is correct
A preceding viral URI causes mucosal edema and ciliary dysfunction that obstruct the sinus ostia.
Blocked ostia trap stagnant secretions, impair mucociliary clearance, and create an environment for bacterial overgrowth (S. pneumoniae, non-typeable H. influenzae, M. catarrhalis).
The "double-sickening" history (viral illness improving, then worsening past day 10 with fever and purulence) and unilateral maxillary tenderness fit this ostiomeatal obstruction mechanism.
Why the others are wrong
IgE-mediated mast cell degranulation of nasal mucosa — this is the mechanism of allergic rhinitis, which produces clear discharge, sneezing, and itch in an atopic patient, not purulent discharge with fever and facial tenderness.
Hematogenous bacterial seeding of the sinus mucosa — ABRS arises from local ostial obstruction and ascending colonization, not blood-borne spread; hematogenous seeding is not the route in routine sinusitis.
Autoimmune granulomatous destruction of nasal cartilage — describes granulomatosis with polyangiitis (saddle-nose deformity, crusting, ulceration with systemic vasculitis), a chronic destructive process rather than an acute post-viral bacterial infection.
Congenital dynein arm defect causing ciliary dysmotility — this is the mechanism of primary ciliary dyskinesia, which is tempting because it also impairs mucociliary clearance, but it is a congenital disorder presenting from early childhood with chronic, recurrent sinusitis, otitis, and bronchiectasis (often with situs inversus), not a single post-viral double-sickening episode in an adult.
Question 2EENTMedium
A 34-year-old man presents with 12 days of nasal congestion, thick yellow-green nasal discharge, and maxillary facial pressure that worsens when he leans forward. His symptoms began with a head cold that briefly improved around day 6 before worsening again with a return of low-grade fever. He has no drug allergies, no recent antibiotic use, and no chronic medical conditions. On exam, temperature is 37.8 C (100.0 F), there is tenderness over the bilateral maxillary sinuses, and anterior rhinoscopy shows purulent discharge and erythematous nasal mucosa. Which of the following is the most appropriate empiric antibiotic?
ACephalexin, oral monotherapy
BTrimethoprim-sulfamethoxazole
CAmoxicillin-clavulanate, oral
DClindamycin, oral monotherapy
EAzithromycin, oral monotherapy
Reveal answer & full explanation
Correct answer: C — Amoxicillin-clavulanate, oral
ACephalexin, oral monotherapy
BTrimethoprim-sulfamethoxazole
CAmoxicillin-clavulanate, oral✓
DClindamycin, oral monotherapy
EAzithromycin, oral monotherapy
Why Amoxicillin-clavulanate, oral is correct
This patient meets clinical criteria for acute bacterial rhinosinusitis (ABRS): symptoms persisting >=10 days plus "double-sickening" (initial improvement followed by worsening with new fever).
IDSA 2012 recommends amoxicillin-clavulanate as first-line empiric therapy, because the beta-lactamase inhibitor covers the rising proportion of beta-lactamase-producing non-typeable Haemophilus influenzae and Moraxella catarrhalis, alongside Streptococcus pneumoniae; AAO-HNS 2015 and ACP/CDC 2016 accept amoxicillin with or without clavulanate as first line.
He has no penicillin allergy and no high-risk features (age <2 or >65, immunocompromised, recent antibiotics), so standard-dose amoxicillin-clavulanate is appropriate.
Why the others are wrong
Cephalexin, oral monotherapy - a first-generation cephalosporin with poor activity against H. influenzae and weaker activity than amoxicillin against S. pneumoniae, so no ABRS guideline recommends it for empiric therapy.
Trimethoprim-sulfamethoxazole - carries high pneumococcal and H. influenzae resistance and is not recommended as empiric monotherapy for ABRS.
Azithromycin, oral monotherapy - pneumococcal macrolide resistance exceeds 25%, so guidelines advise against macrolide monotherapy for ABRS.
Clindamycin, oral monotherapy - clindamycin covers many S. pneumoniae strains and oral anaerobes, which makes it tempting for a sinus infection, but it lacks activity against H. influenzae and M. catarrhalis, so no ABRS guideline recommends it as empiric monotherapy.
Additional high-yield points
Plain amoxicillin is an acceptable first-line alternative for a low-risk adult under AAO-HNS 2015 and ACP/CDC 2016; high-dose amoxicillin-clavulanate is favored when resistance risk factors are present (age >65, antibiotics in the past month, recent hospitalization, immunocompromise).
For an adult with a penicillin allergy, doxycycline or a respiratory fluoroquinolone is the usual alternative.
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Dental abscess — Maxillary tooth pain with percussion, periapical lucency on dental imaging; treat underlying tooth
Migraine or tension headache — Recurrent headache with photophobia/phonophobia or scalp tension; no purulent discharge or fever
Invasive fungal sinusitis (mucormycosis) — Immunocompromised or poorly controlled diabetic with rapid facial pain, black eschar on turbinate or palate, cranial neuropathies; emergent ENT/surgical debridement + IV amphotericin B
Nasal foreign body — Unilateral purulent foul discharge in a child
Trigeminal neuralgia — Lancinating facial pain triggered by light touch; no purulent discharge
Diagnostic workup
Diagnostic criteria
IDSA 2012 (AAO-HNSF 2025 uses criteria 1 and 3) — ABRS if ANY of: (1) symptoms ≥10 days without improvement, (2) severe symptoms — purulent discharge or facial pain with fever ≥39°C (102°F) for ≥3-4 consecutive days at illness onset, or (3) 'double-sickening' — new fever, headache, or increased nasal discharge after a viral URI that had begun improving.
Labs
ABRS is a clinical diagnosis — no routine labs
Consider CBC, blood cultures if complications suspected
Sinus aspirate culture (otolaryngologist) reserved for treatment failure, immunocompromised, or complicated disease
Imaging
Not routinely indicated in uncomplicated ABRS
CT sinus without contrast if complications suspected, treatment failure, recurrent disease, or surgical planning
CT or MRI with contrast for orbital cellulitis, cavernous sinus thrombosis, brain abscess
Plain sinus films and ultrasound have largely been abandoned
Diagnostic algorithm
flowchart TD
A[URI / sinus symptoms] --> B{Symptom duration<br/>and pattern}
B -->|<10 days, improving| C[Viral rhinosinusitis<br/>Supportive care]
B -->|≥10 days no improvement| D[ABRS]
B -->|Severe onset ≥3-4 d<br/>T≥39 + purulent discharge<br/>or facial pain| D
B -->|Double-sickening<br/>worse after improvement| D
D --> E{Risk factors<br/>for resistance?}
E -->|Yes| G["High-dose amox-clav<br/>age under 2 or over 65, recent antibiotics,<br/>daycare, immunocompromised, severe"]
E -->|No, adult| F["Watchful waiting with follow-up<br/>OR amoxicillin ± clavulanate 5-7 d"]
E -->|No, child| M["Standard-dose amoxicillin ± clavulanate<br/>45 mg/kg/day, or 3-day observation<br/>if persistent illness only"]
F --> H{Improved by 3-5 d?}
G --> H
M --> H
H -->|Yes| I[Complete course]
H -->|No or worse| J[Start or switch antibiotic<br/>± CT sinus<br/>± ENT referral]
D --> K{Red flags?<br/>Orbital/intracranial/<br/>immunocompromised}
K -->|Yes| L[Urgent CT/MRI<br/>IV antibiotics<br/>ENT/Ophtho]
Diagnosis and management algorithm for acute bacterial rhinosinusitis.
Treatment
First-line
Symptomatic care for ALL: saline nasal irrigation, intranasal corticosteroid (fluticasone, mometasone), analgesics (acetaminophen, NSAIDs), adequate hydration; decongestants optional for short-term relief only (IDSA advises against routine use; topical oxymetazoline ≤3 days to avoid rebound congestion)
AAO-HNSF 2025 recommends offering watchful waiting (no antibiotic) to adults with uncomplicated ABRS regardless of severity when follow-up is assured; start an antibiotic if no improvement by 3-5 days or worsening at any time
First-line antibiotic: amoxicillin-clavulanate 500/125 mg TID or 875/125 mg BID × 5-7 days (adults); 45 mg/kg/day amoxicillin component for children — IDSA recommends amox-clav OVER amoxicillin alone due to rising H. influenzae beta-lactamase rates (AAO-HNSF 2025 accepts amoxicillin with or without clavulanate)
High-dose amoxicillin-clavulanate (2 g BID adults; 90 mg/kg/day amoxicillin component children) for: severe infection, immunocompromised, recent antibiotic use, age <2 or >65, daycare, prior hospitalization, region with >10% PCN-resistant S. pneumoniae
Second-line / adjunct
Penicillin allergy (non-anaphylactic): doxycycline (adults), or cefuroxime/cefpodoxime/cefdinir
Severe penicillin allergy: doxycycline OR levofloxacin/moxifloxacin (reserve fluoroquinolones — FDA boxed warnings)
Treatment failure at 72 h: switch to higher-dose amox-clav, doxycycline, or levofloxacin; consider CT and ENT referral
Avoid macrolides (azithromycin, clarithromycin) and TMP-SMX as monotherapy due to high pneumococcal resistance
Refer to ENT for: orbital/intracranial complications, recurrent ABRS (≥4 episodes/year), anatomic abnormality, immunocompromised
Complications
Orbital cellulitis or abscess (especially ethmoid sinusitis in children) — proptosis, ophthalmoplegia, vision loss
Invasive fungal sinusitis in immunocompromised — mucormycosis, aspergillosis
Progression to chronic rhinosinusitis
PANCE pearls
Distinguishing viral from bacterial sinusitis: duration ≥10 days, double-sickening, or severe high-fever onset with purulent discharge ≥3-4 days.
IDSA 2012 recommends amoxicillin-clavulanate over amoxicillin alone — most boards updated to this answer.
Avoid macrolides and TMP-SMX as monotherapy — >25% pneumococcal resistance.
Periorbital swelling + decreased EOM + proptosis = orbital cellulitis → IV antibiotics + CT + ophthalmology/ENT.
Black necrotic eschar on palate or turbinates in a diabetic or immunocompromised patient = mucormycosis — emergent surgical debridement and IV amphotericin B.
Intranasal corticosteroids improve symptoms in ABRS as adjunct therapy.
References
IDSA 2012 — Chow AW et al. IDSA Clinical Practice Guideline for Acute Bacterial Rhinosinusitis. Clin Infect Dis 2012;54(8):e72-e112
AAO-HNSF 2025 — Payne SC et al. Clinical Practice Guideline: Adult Sinusitis Update. Otolaryngol Head Neck Surg 2025;173(Suppl 1):S1-S56
AAP 2013 — Wald ER et al. Clinical Practice Guideline for the Diagnosis and Management of Acute Bacterial Sinusitis in Children Aged 1 to 18 Years. Pediatrics 2013
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