Infectious Disease and Microbiology – Sinusitis

Sinusitis, more accurately termed rhinosinusitis, is symptomatic inflammation of the mucosa of the nasal cavity and paranasal sinuses. The major paranasal sinuses are the maxillary, ethmoid, frontal, and sphenoid sinuses.

Classification by Duration

Acute rhinosinusitis: symptoms lasting <4 weeks.

Subacute rhinosinusitis: symptoms lasting approximately 4–12 weeks.

Chronic rhinosinusitis (CRS): symptoms persisting for ≥12 weeks.

Recurrent acute rhinosinusitis: ≥4 distinct episodes per year, with resolution of symptoms between episodes.

Acute exacerbation of chronic rhinosinusitis: worsening or development of new symptoms in a patient with underlying chronic disease.

Acute rhinosinusitis is overwhelmingly viral. Only a small proportion of viral upper respiratory infections develop secondary acute bacterial rhinosinusitis (ABRS).

The most important bacterial causes of community-acquired acute bacterial rhinosinusitis are:

1. Streptococcus pneumoniae

2. Nontypeable Haemophilus influenzae

3. Moraxella catarrhalis — particularly important in children.

Other organisms, including Staphylococcus aureus, streptococci, anaerobes, and gram-negative bacilli, become more relevant in particular clinical settings.

Odontogenic sinusitis is commonly polymicrobial and may contain oral anaerobic organisms in addition to aerobic bacteria. It particularly involves the maxillary sinus because of its anatomical relationship to the upper teeth.

Important risk factors include allergic rhinitis, smoking and environmental irritants, nasal polyps, deviated nasal septum, tumors, foreign bodies, impaired mucociliary clearance, cystic fibrosis, immunodeficiency, and dental infection.

The pathogenesis frequently begins with a viral upper respiratory infection.

Viral inflammation produces mucosal edema → obstruction of sinus ostia → impaired sinus drainage → retention of secretions → impaired mucociliary clearance.

These conditions may subsequently permit secondary bacterial infection.

A key clinical challenge is distinguishing viral rhinosinusitis from acute bacterial rhinosinusitis because purulent nasal secretions alone do not reliably indicate bacterial infection.

When to Suspect Acute Bacterial Rhinosinusitis

Three clinical patterns are particularly useful.

Persistent illness: nasal discharge or daytime cough/facial pressure persists for approximately 10 days or longer without improvement.

Severe onset: prominent fever with purulent nasal discharge or significant facial pain persisting for several consecutive days at the beginning of illness.

“Double worsening”: the patient initially improves from a viral upper respiratory infection and then develops new or worsening fever, nasal discharge, facial pain, or cough.

This is sometimes called double sickening.

Typical symptoms include nasal obstruction/congestion, anterior or posterior nasal discharge, facial pressure or pain, reduced sense of smell, headache, cough, halitosis, and occasionally fever.

Maxillary tooth pain, particularly when unilateral, may support maxillary sinus involvement. Dental pathology should also raise suspicion for an odontogenic source.

Pain or pressure may occur over the affected sinus and sometimes becomes more noticeable when bending forward, although this finding is not sufficiently specific to establish the diagnosis.

Chronic rhinosinusitis typically presents with prolonged nasal obstruction, nasal drainage, facial pressure, and/or reduced smell, with objective evidence of sinonasal inflammation required to support the diagnosis.

Chronic rhinosinusitis is commonly divided into:

CRS with nasal polyps (CRSwNP)

and

CRS without nasal polyps (CRSsNP).

Chronic rhinosinusitis with nasal polyps is strongly associated with type 2 airway inflammation, and frequently coexists with asthma.

The combination of asthma + chronic rhinosinusitis with nasal polyps + respiratory reactions to aspirin/other COX-1–inhibiting NSAIDs suggests aspirin-exacerbated respiratory disease (AERD).

Diagnosis

Most uncomplicated cases of acute rhinosinusitis are diagnosed clinically.

Routine laboratory testing is usually unnecessary.

Plain sinus radiographs are generally not recommended for routine diagnosis because imaging abnormalities cannot reliably distinguish viral from bacterial rhinosinusitis.

Similarly, CT should not routinely be performed for uncomplicated acute bacterial rhinosinusitis.

A CT scan of the paranasal sinuses becomes important when complications are suspected, symptoms are recurrent or chronic, the diagnosis is uncertain, or surgical planning is required.

CT findings can include mucosal thickening, sinus opacification, air-fluid levels, polyps, and obstruction of sinus drainage pathways.

MRI is particularly useful when there is concern for orbital, intracranial, soft-tissue, vascular, or invasive fungal complications.

Routine cultures of ordinary nasal secretions are poor predictors of organisms within the affected sinus and generally should not guide antibiotic therapy.

When microbiologic diagnosis is necessary because of severe disease, treatment failure, immunocompromise, unusual organisms, or complications, specimens obtained by sinus aspiration or endoscopically directed middle-meatal sampling are substantially more useful.

Treatment of Acute Viral Rhinosinusitis

Most cases require supportive treatment rather than antibiotics.

Useful measures can include analgesics, saline nasal irrigation, and intranasal corticosteroids, particularly when concomitant allergic rhinitis is present.

Topical nasal decongestants such as oxymetazoline can provide temporary symptomatic relief but should generally be limited to a short course because prolonged use can produce rhinitis medicamentosa (rebound congestion).

Antihistamines are most useful when an allergic component is present. They are not routinely necessary simply because a patient has acute infectious sinusitis.

Treatment of Acute Bacterial Rhinosinusitis

When antibiotics are indicated, amoxicillin-clavulanate is commonly preferred as initial empiric therapy.

Antibiotic selection should consider age, severity, allergy history, recent antimicrobial exposure, local resistance patterns, comorbidities, and risk for resistant organisms.

A major change from older recommendations is that macrolides such as azithromycin and clarithromycin and trimethoprim-sulfamethoxazole are generally not preferred for empiric ABRS because of substantial antimicrobial resistance among common respiratory pathogens.

Respiratory fluoroquinolones such as levofloxacin or moxifloxacin have activity against common pathogens but are generally reserved for selected situations, including certain patients with significant beta-lactam allergy, because of their adverse-effect profile and antimicrobial-stewardship considerations.

For uncomplicated ABRS in adults, contemporary practice generally favors a shorter antibiotic course when the patient responds appropriately rather than the routinely prolonged 10–14-day courses used historically.

Chronic Rhinosinusitis

The management of chronic rhinosinusitis differs substantially from acute bacterial sinusitis because CRS is primarily a chronic inflammatory disorder, not simply a persistent bacterial infection.

Core medical therapy includes saline nasal irrigation and intranasal corticosteroids.

Antibiotics are not routinely required for every patient with chronic rhinosinusitis and are used selectively according to the clinical circumstances.

Short courses of systemic corticosteroids may be considered in selected patients, particularly those with severe nasal polyposis, but their risks must be considered.

Patients with persistent disease despite appropriate medical treatment may require ENT evaluation and functional endoscopic sinus surgery (FESS).

Invasive Fungal Rhinosinusitis

Acute invasive fungal rhinosinusitis is a medical and surgical emergency.

It occurs predominantly in patients with profound immunocompromise, uncontrolled diabetes—especially diabetic ketoacidosis—or other major predisposing conditions.

Important pathogens include fungi of the order Mucorales (Rhizopus, Mucor, and related organisms) and Aspergillus species.

Warning manifestations include severe facial pain, facial swelling, fever, ophthalmoplegia, visual abnormalities, cranial nerve abnormalities, and necrotic tissue of the nasal cavity or palate.

A black necrotic eschar in an appropriate high-risk patient is particularly concerning, although its absence does not exclude invasive fungal disease.

Suspected invasive fungal rhinosinusitis requires urgent ENT evaluation, nasal endoscopy, tissue biopsy for histopathology and culture, appropriate imaging, systemic antifungal therapy, and aggressive surgical debridement of necrotic tissue.

For mucormycosis, a lipid formulation of amphotericin B is a major initial treatment option. For invasive aspergillosis, voriconazole is an important first-line antifungal agent.

Complications

Although uncommon, complications of bacterial sinusitis can be life-threatening because of the close anatomical relationship of the sinuses to the orbit, brain, meninges, and intracranial venous system.

Orbital complications are particularly associated with ethmoid sinusitis and include preseptal cellulitis, orbital cellulitis, subperiosteal abscess, and orbital abscess.

Important warning signs are periorbital swelling, proptosis, ophthalmoplegia, pain with eye movement, diplopia, or decreased visual acuity.

These findings warrant urgent evaluation.

Frontal sinusitis can rarely produce osteomyelitis of the frontal bone with a subperiosteal abscess, producing the characteristic forehead swelling known as Pott puffy tumor.

Intracranial complications include meningitis, brain abscess, epidural abscess, subdural empyema, and septic cavernous sinus thrombosis.

A patient with sinusitis who develops severe or progressive headache, altered mental status, meningismus, focal neurologic deficits, seizures, orbital abnormalities, or significant facial swelling requires urgent evaluation for complications.

High-Yield Clinical Pattern

Viral URI → mucosal edema → sinus ostial obstruction → impaired drainage → secondary bacterial infection in a minority of patients.

Symptoms <10 days and improving → usually viral → supportive treatment.

≥10 days without improvement → consider acute bacterial rhinosinusitis.

Severe onset → consider acute bacterial rhinosinusitis.

Initial improvement followed by worsening (“double worsening”) → consider acute bacterial rhinosinusitis.

Most important ABRS organisms:

S. pneumoniae + H. influenzae + M. catarrhalis (especially children).

Typical empiric first-line antibiotic when indicated:

Amoxicillin-clavulanate.

Orbital signs, neurologic abnormalities, severe headache, or immunocompromised patient with necrotic nasal tissue → investigate urgently for a complicated or invasive infection.