# Acute Sinusitis

Acute rhinosinusitis is usually viral; identify the clinical patterns that increase the likelihood of bacterial disease, reserve imaging for complications or alternative diagnoses, and use watchful waiting or targeted antibiotics with defined reassessment and escalation thresholds.

**Clinical question:** How should clinicians distinguish uncomplicated viral from bacterial acute rhinosinusitis and select observation, antibiotics, imaging, or urgent referral?

Updated: 2026-08-21T02:05:00.373316+00:00

## What matters in practice
- Diagnose acute bacterial rhinosinusitis clinically when symptoms are persistent for more than 10 days without improvement, severe for more than 3-4 days with fever at least 39°C plus purulent nasal discharge or facial pain, or worsen after initial improvement of a viral URI. [18][3]
- Do not obtain routine sinus radiographs for uncomplicated acute rhinosinusitis; imaging is reserved for suspected orbital, intracranial, invasive fungal, neoplastic, or other complicated disease. [18][15][16]
- For uncomplicated bacterial presentations with reliable follow-up, watchful waiting is appropriate; start antibiotics if symptoms worsen or fail to improve during the observation interval. [18][15]
- When antibiotics are selected, amoxicillin or amoxicillin-clavulanate is first-line; reassess for clinical improvement within 48-72 hours after treatment initiation. [18][15]
- Persistent fever above 39°C, altered mental status, ocular findings, or suspected neurologic complications require urgent specialty-directed evaluation rather than routine outpatient management. [16]

## Identify orbital, intracranial, and invasive disease before outpatient treatment

Escalate promptly when examination or host factors suggest disease beyond uncomplicated mucosal infection.

Do not manage as routine outpatient acute sinusitis when there is altered mental status, suspected meningitis or intracranial abscess, orbital cellulitis, intraorbital abscess, or cavernous sinus thrombosis. Persistent fever greater than 39°C is also a severe feature requiring reassessment for complicated disease. Arrange urgent specialty evaluation when these findings are present. [16]

Treat acute invasive fungal paranasal sinusitis as a surgical and systemic antifungal emergency in severely immunocompromised patients. IDSA recommends surgical debridement plus systemic antifungal therapy; voriconazole is preferred, with a lipid formulation of amphotericin B as an alternative. Debridement may need to be repeated, and extensive surgery is best deferred until thrombocytopenia resolves when feasible because postoperative hemorrhage risk is increased. [24]

Refer patients with immunocompromise, obstructive anatomic defects, recurrent sinusitis, suspected fungal sinusitis, or suspected neoplasm for specialist assessment rather than repeated empiric outpatient antibiotic courses. [16]
- Urgent escalation triggers: altered mental status; suspected orbital cellulitis or intraorbital abscess; cavernous sinus thrombosis; meningitis; intracranial abscess. [16]
- High-risk invasive fungal context: severe immunocompromise with acute paranasal sinusitis. [24]
- Potential invasive fungal extension: proptosis or extension toward the orbit or brain. [24]

*Clinical findings that redirect acute sinusitis from routine outpatient care. [16][24]*

| Finding or context | Most consequential concern | Next action |
| --- | --- | --- |
| Altered mental status or suspected meningitis/intracranial abscess [16] | Intracranial complication [16] | Urgent specialty-directed evaluation. [16] |
| Orbital cellulitis, intraorbital abscess, or cavernous sinus thrombosis suspected [16] | Orbital or cavernous sinus complication [16] | Urgent specialty-directed evaluation. [16] |
| Severely immunocompromised patient with acute sinusitis [24] | Acute invasive fungal paranasal sinusitis [24] | Urgent surgical debridement plus systemic voriconazole or lipid amphotericin B. [24] |
| Proptosis or possible orbit/brain extension [24] | Chronic invasive or granulomatous aspergillosis; invasive extension [24] | Specialist-directed diagnostic and surgical management with systemic antifungal therapy. [24] |

## Use illness trajectory rather than isolated symptoms to diagnose bacterial disease

Most cases are viral, and purulence or facial pressure alone does not establish a bacterial infection.

Acute bacterial rhinosinusitis is a clinical diagnosis. Use one of three patterns: persistent nasal discharge or daytime cough for more than 10 days without improvement; severe illness for more than 3-4 consecutive days with fever at least 39°C and purulent nasal discharge or facial pain; or worsening/new fever, daytime cough, or nasal discharge after initial improvement from a viral URI lasting 5-6 days. [18][3]

The decision threshold should account for the natural history of viral illness: uncomplicated viral URIs generally peak around days 3-6 and are resolving by approximately days 5-7, although residual symptoms can extend beyond 10 days. A nonresolving course, rather than duration alone, supports bacterial disease. [13]

Overall clinician impression and dental pain are among the clinical findings most suggestive of acute bacterial rhinosinusitis; overall clinical impression has a positive likelihood ratio of 3.9. Use these findings to refine probability, but retain the trajectory-based criteria before committing to antibacterial treatment. [5]
- Persistent pattern: symptoms for more than 10 days without clinical improvement. [18][3]
- Severe pattern: fever at least 39°C with purulent nasal discharge or facial pain lasting more than 3-4 days. [18][3]
- Double-worsening pattern: new or worsening fever, cough, or nasal discharge after initial improvement of a 5-6-day viral URI. [18][3]
- Viral predominance: 90%-98% of rhinosinusitis cases are viral. [18]

*Trajectory-based approach to acute rhinosinusitis. [18][3][13]*

| Clinical trajectory | Interpretation | Management implication |
| --- | --- | --- |
| Symptoms peak at days 3-6 and are improving [13] | Typical uncomplicated viral URI pattern [13] | Provide symptomatic management; do not diagnose bacterial sinusitis solely from nasal symptoms. [13][18] |
| Symptoms persist >10 days without improvement [18][3] | Clinical acute bacterial rhinosinusitis pattern [18][3] | Offer watchful waiting if reliable follow-up is available or initiate first-line antibiotic therapy. [18][15] |
| Fever ≥39°C plus purulent discharge or facial pain for >3-4 days [18][3] | Severe bacterial pattern [18][3] | Treat as acute bacterial rhinosinusitis and assess for severe or complicated disease. [18][16] |
| New or worsening symptoms after initial improvement from URI [18][3] | Double-worsening bacterial pattern [18][3] | Offer watchful waiting with reliable follow-up or initiate first-line antibiotic therapy. [18][15] |

## Avoid routine imaging in uncomplicated disease and image when the result changes disposition

Imaging does not distinguish routine viral from bacterial acute rhinosinusitis sufficiently to guide usual outpatient care.

Do not order sinus radiographs routinely for acute rhinosinusitis. Clinical criteria determine whether acute bacterial rhinosinusitis is likely, and routine imaging is not recommended in uncomplicated cases. [18][15]

Obtain targeted imaging when complications, an alternative diagnosis, or a high-risk process is suspected. CT detects isolated sphenoid sinus disease more consistently than plain films, whereas plain films can miss approximately half of sphenoid sinusitis cases; use this distinction when localizing suspected deep sinus disease rather than relying on routine radiography. [12]

In a patient with persistent or recurrent symptoms, separate acute episodes with complete clinical resolution from chronic rhinosinusitis. Chronic rhinosinusitis persists for at least 12 weeks, while recurrent acute disease is characterized by discrete episodes with symptom-free intervals and normalization between attacks. [7][8][12]
- Do not use sinus radiographs as a routine test for uncomplicated acute rhinosinusitis. [18]
- Use CT when suspected sphenoid disease, orbital/intracranial complication, neoplasm, or invasive fungal disease would change management. [12][16][24]
- Reclassify symptoms persisting at least 12 weeks as chronic rhinosinusitis rather than acute bacterial rhinosinusitis. [7][8][9]

*When imaging meaningfully changes management. [12][16][18][24]*

| Clinical setting | Imaging approach | Reason for imaging |
| --- | --- | --- |
| Uncomplicated acute rhinosinusitis meeting clinical criteria [18] | No routine sinus radiograph. [18] | Imaging is not routinely recommended. [18] |
| Suspected isolated sphenoid sinus disease [12] | CT rather than plain film. [12] | Plain films may miss about 50% of sphenoid sinusitis; CT consistently detects it. [12] |
| Ocular, neurologic, or mental-status abnormality [16] | Urgent complication-directed imaging with specialty involvement. [16] | Evaluate for orbital, cavernous sinus, or intracranial complications. [16] |
| Severe immunocompromise or suspected invasive fungal disease [24] | Urgent imaging as part of surgical and antifungal planning. [24] | Define invasive disease and possible orbital or cerebral extension. [24] |

## Choose observation or antibiotics based on bacterial pattern, severity, and follow-up reliability

Antibiotics offer limited benefit for many clinically diagnosed cases, so observation is a deliberate treatment strategy.

For uncomplicated acute bacterial rhinosinusitis with reliable follow-up, encourage watchful waiting. The American Academy of Otolaryngology-Head and Neck Surgery approach permits either antibiotics or a 7-day observation period, with antibiotics started if symptoms worsen or fail to improve. [15] About 65% of patients thought to have acute bacterial rhinosinusitis who receive placebo improve spontaneously, supporting an observation option when follow-up is dependable. [16]

If antibiotic treatment is selected, prescribe amoxicillin or amoxicillin-clavulanate as first-line therapy. IDSA recommends amoxicillin-clavulanate after a clinical diagnosis of acute bacterial rhinosinusitis; clavulanate expands coverage for beta-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis. [18][15] A cited adult standard-dose regimen is amoxicillin-clavulanate 875 mg/125 mg orally twice daily for 7 days. [17]

Avoid macrolides, including azithromycin, because Streptococcus pneumoniae resistance is approximately 40%. For penicillin-allergic adults, doxycycline or a respiratory fluoroquinolone, levofloxacin or moxifloxacin, are listed alternatives. [18] Reassess symptoms within 48-72 hours after starting amoxicillin-clavulanate; failure to improve should trigger diagnostic reassessment and an antibiotic change rather than simply extending the same regimen. [15]
- Watchful waiting: use only for uncomplicated illness when reliable follow-up is available; begin antibiotics for worsening or failure to improve during a 7-day observation period. [18][15]
- First-line options: amoxicillin or amoxicillin-clavulanate. [18]
- Cited adult amoxicillin-clavulanate regimen: 875 mg/125 mg orally twice daily for 7 days. [17]
- Do not use azithromycin empirically for acute bacterial rhinosinusitis because of high pneumococcal resistance. [18]
- Reassess 48-72 hours after antibiotic initiation. [15]

### Treatment failure after initial antibiotics

When an adult treated with amoxicillin-clavulanate does not improve at reassessment, change therapy to high-dose amoxicillin-clavulanate, doxycycline, a respiratory fluoroquinolone such as levofloxacin or moxifloxacin, or clindamycin plus a third-generation oral cephalosporin. At the same visit, reconsider an alternative diagnosis, obstructive anatomy, recurrent disease, fungal disease, or neoplasm, particularly if symptoms are atypical or recurrent. [15][16]
- Do not interpret lack of improvement as an automatic indication for repeat routine imaging; image when complications or an alternative structural diagnosis is suspected. [15][16]
- Refer rather than serially change antibiotics when recurrent sinusitis, obstructive anatomy, fungal disease, immunocompromise, or neoplasm is suspected. [16]

*Antibiotic selection and reassessment for clinically diagnosed acute bacterial rhinosinusitis. [15][17][18]*

| Situation | Action | Timing or caution |
| --- | --- | --- |
| Uncomplicated bacterial pattern with reliable follow-up [18][15] | Watchful waiting or first-line antibiotic therapy. [18][15] | If observing, start antibiotics for worsening or failure to improve during 7 days. [15] |
| First-line treatment selected [18][15] | Amoxicillin or amoxicillin-clavulanate; cited adult regimen: 875/125 mg orally twice daily for 7 days. [18][17] | Monitor response within 48-72 hours. [15] |
| Penicillin allergy [18] | Doxycycline, levofloxacin, or moxifloxacin. [18] | Avoid macrolides because pneumococcal resistance is approximately 40%. [18] |
| No improvement after amoxicillin-clavulanate [15] | Change to high-dose amoxicillin-clavulanate, doxycycline, respiratory fluoroquinolone, or clindamycin plus a third-generation oral cephalosporin. [15] | Reassess diagnosis and evaluate for alternate or complicated disease. [15][16] |

## Use local symptom therapies selectively and recognize fungal phenotypes

Adjunctive treatment should not obscure deterioration or substitute for escalation in high-risk disease.

For acute bacterial rhinosinusitis, use nasal saline irrigation and intranasal glucocorticoids as adjuncts. IDSA does not recommend decongestants or antihistamines as adjunctive treatment for acute bacterial rhinosinusitis. [15] Analgesics, including acetaminophen and nonsteroidal anti-inflammatory drugs, are symptomatic options during observation or alongside antibacterial therapy. [15]

Consider allergic fungal rhinosinusitis in chronic rather than routine acute presentations with nasal polyposis and characteristic eosinophilic mucin containing fungal hyphae. Fungal culture of nasal secretions is usually unhelpful because it commonly reflects airborne fungi rather than the causative process. Allergic fungal rhinosinusitis can produce ophthalmic involvement, bony erosion, or cavernous venous thrombosis, which should prompt specialty-directed evaluation. [24]

Do not treat a chronic symptom pattern as repeated acute bacterial sinusitis. Chronic rhinosinusitis has evidence supporting saline lavage and intranasal steroids; this is a separate management pathway from short-course antibacterial treatment for acute bacterial disease. [23][9]
- Adjuncts for acute bacterial rhinosinusitis: saline irrigation and intranasal glucocorticoids. [15]
- Avoid routine decongestants and antihistamines as adjunctive therapy for acute bacterial rhinosinusitis under IDSA recommendations. [15]
- For suspected allergic fungal rhinosinusitis, do not rely on nasal secretion fungal culture to establish causation. [24]

*Distinguishing acute bacterial, chronic inflammatory, and fungal rhinosinusitis pathways. [9][23][24]*

| Pattern | Discriminator | Next step |
| --- | --- | --- |
| Acute bacterial rhinosinusitis [18] | Persistent >10 days without improvement, severe fever/purulence/facial pain pattern, or double worsening. [18] | Observation with reliable follow-up or first-line amoxicillin/amoxicillin-clavulanate. [18][15] |
| Chronic rhinosinusitis [9][23] | Symptoms persist at least 12 weeks. [9] | Use chronic-rhinosinusitis evaluation and medical management; saline lavage and intranasal steroids have the highest level of evidence among cited treatments. [23] |
| Allergic fungal rhinosinusitis [24] | Nasal polyposis with eosinophilic mucin and fungal hyphae; possible bony or ophthalmic complications. [24] | Specialty-directed assessment; nasal secretion fungal culture is usually unhelpful. [24] |
| Acute invasive fungal sinusitis [24] | Severe immunocompromise with acute disease, with possible orbit or brain extension. [24] | Urgent debridement plus systemic voriconazole or lipid amphotericin B. [24] |

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## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.