Acute Rhinosinusitis

Acute rhinosinusitis is symptomatic inflammation of the nasal cavity and one or more paranasal sinuses, lasting 4 weeks or less.^[1] Most episodes are triggered by a viral upper respiratory tract infection; bacterial invasion of the sinuses complicates only 0.5-2% of adult cases and 6-13% of pediatric cases. The default management for uncomplicated acute rhinosinusitis is symptom control without antibiotics — about 70% of cases resolve within 2 weeks regardless of antibiotic use, and the 2025 AAO-HNSF guideline update recommends clinicians offer watchful waiting (not merely consider it) for uncomplicated disease with assured follow-up.^[2] Antibiotics do not reduce the rare risk of orbital or intracranial complications, so preventing complications is never, on its own, a reason to prescribe one.

Typical presentation — the PODS mnemonic (adults)

• Pain (facial), particularly when bending forward.
• Obstruction (nasal obstruction, blockage, congestion).
• Discharge (purulent nasal drainage, anterior and/or posterior).
• Smell disorder (reduced or lost sense of smell).

Patients may also have sore throat, cough, malaise, tooth pain, or fever. Children more often present with sudden onset of 2 or more of: discoloured nasal drainage, nasal obstruction, and/or cough (day or night).

Etiology

Most commonly triggered by rhinovirus, adenovirus, influenza, or parainfluenza virus, causing local inflammation, edema, mucus production, and sinus obstruction. In a small proportion of cases this permits bacterial invasion — Streptococcus pneumoniae, non-typeable Haemophilus influenzae, and Moraxella catarrhalis are the most common bacterial pathogens in both children and adults.

Differentiating from allergic rhinitis

Ask specifically about sneezing, watery rhinorrhea or watery/itchy eyes, and nasal or ocular pruritus — these point toward allergic rhinitis rather than rhinosinusitis. Sinus pain or headache without nasal symptoms should prompt consideration of dental disease or a primary headache syndrome instead.

• Recent viral upper respiratory tract infection.
• Environmental irritant exposure, especially tobacco smoke.
• Allergen exposure/allergic rhinitis.
• Anatomic anomalies of the nasal cavity/sinuses.
• Immunocompromise.
• Pregnancy — hormone-induced nasal congestion and pregnancy-related immune changes raise the risk of bacterial rhinosinusitis roughly 6-fold versus the nonpregnant population, peaking in the second trimester; classic signs and symptoms are absent in nearly half of pregnant patients with confirmed purulent rhinosinusitis, so have a lower threshold to evaluate.

Diagnosis is clinical

Diagnosis relies on history with or without physical exam. Additional investigations are not needed in patients without features suggestive of complicated disease — radiography cannot distinguish viral from bacterial infection and is not recommended for routine diagnosis; nasal swabs are contaminated by normal flora and do not predict the true sinus pathogen; direct sinus aspiration is rarely performed outside of research or complicated cases.

The single most important diagnostic decision: viral or bacterial?

No individual symptom is diagnostic of bacterial involvement — fever occurs in both, and the colour of nasal discharge reflects the presence of neutrophils, not bacteria specifically. Diagnose acute bacterial rhinosinusitis based on the time course of illness, not the symptom pattern:

• Symptoms of acute rhinosinusitis persisting without improvement for more than 10 days after URTI symptom onset, OR
• Symptoms that worsen within 10 days after an initial period of improvement — "double sickening."

Severity classification (changes the escalation ladder)

Severe: at least 3 consecutive days of high fever (≥39°C) plus purulent nasal discharge or facial pain, especially in adults — this, or immunocompromise, moves a patient to a different (more aggressive) treatment tier regardless of the 10-day rule.

Examination

Posterior rhinoscopy may show nasal inflammation, mucosal edema, or purulent discharge; sinus tenderness may be present on palpation. Physical exam should specifically look for the red-flag findings above, which are more useful for excluding complications than for confirming the diagnosis itself.

• Reduce symptoms.
• Eradicate infection when bacterial and antibiotics are indicated.
• Prevent recurrence.
• Minimize unnecessary antibiotic use to limit resistance and adverse effects.

• Saline nasal irrigation — thins mucus, clears inflammatory mediators, improves mucociliary function, and moisturizes inflamed mucosa. No irrigation method has been shown clearly superior, though one adult study found large-volume irrigation (250 mL) more effective for rhinorrhea and postnasal drip than small-volume syringe irrigation (10 mL).
• Comfort measures without formal efficacy data but commonly recommended: adequate rest and hydration, warm facial packs/compresses, sleeping with the head of the bed elevated.
• Prevention: limit spread of viral infection (hand hygiene, and physical distancing/masking during a viral epidemic); avoid tobacco smoke and other environmental irritants; reduce allergen exposure.

Pregnancy

Pregnancy rhinitis (hormone-driven congestion mimicking rhinosinusitis) usually resolves within 2 weeks postpartum and should be distinguished from true bacterial rhinosinusitis, which is roughly 6-fold more common in pregnancy and often lacks classic symptoms. Nonpharmacologic measures (saline irrigation) first; acetaminophen for pain/fever; NSAIDs are an alternative but avoid in the second half of pregnancy (ductus arteriosus closure risk in the third trimester, oligohydramnios risk ≥20 weeks). No evidence supports decongestants for rhinosinusitis symptom relief in pregnancy; if used, topical is preferred over oral, minimally (e.g., only at bedtime) for no more than 3-5 days, preferably after the first trimester — avoid oral decongestants in the first trimester (possible gastroschisis risk). Amoxicillin is first-line for confirmed bacterial disease; amoxicillin/clavulanate is safe after amoxicillin failure; cefuroxime for type I/nonsevere type IV penicillin allergy; azithromycin if unable to take any beta-lactam. Avoid fluoroquinolones (safer alternatives usually available), doxycycline (fetal tooth discoloration), clarithromycin (miscarriage risk), and sulfamethoxazole/trimethoprim (neural tube defect risk), particularly in the first trimester.

Breastfeeding

Saline irrigation first-line. Acetaminophen or ibuprofen for pain/fever. Topical decongestants (oxymetazoline, xylometazoline, phenylephrine) considered safe for ≤3-5 days; use oral decongestants cautiously (reduced milk production reported) and only short-acting forms taken right after a feed if needed; watch the infant for irritability, nervousness, insomnia, or excitation. Intranasal corticosteroids are considered safe given minimal absorption. Amoxicillin and amoxicillin/clavulanate are compatible with breastfeeding; cefuroxime or a macrolide are options if amoxicillin cannot be used; use caution with doxycycline, levofloxacin, and moxifloxacin, avoiding repeated/prolonged exposure. Watch the breastfed infant for thrush, rash, or diarrhea with any antibiotic.

Recent antibiotic use

Antibiotic exposure within the prior 3 months is a risk factor for resistant S. pneumoniae, especially to macrolides and fluoroquinolones — choose a different antibiotic class if this applies.

Inform patients that improvement, not full resolution, within 7 days is the marker of treatment efficacy — complete symptom resolution can take up to 21 days. Routine follow-up after completing therapy is not needed in an asymptomatic patient. If the patient deteriorates at any point, reassess for a complication (see Red Flags), an alternative diagnosis, or nonadherence rather than simply extending or escalating therapy.

1. Reassess the diagnosis — confirm this is still acute bacterial rhinosinusitis, not a complication, dental source, or primary headache syndrome.
2. Treatment failure is defined as no improvement after 3-5 days of an appropriate antibiotic (2025 AAO-HNSF), or up to 7 days by older criteria — reassess promptly rather than waiting the full week if the patient is worsening.
3. If failed on amoxicillin (standard- or high-dose): switch to amoxicillin/clavulanate (with additional amoxicillin if the prior failure was on high-dose amoxicillin, amoxicillin/clavulanate alone is adequate).
4. If penicillin-allergic and failed doxycycline/cefuroxime: consider clindamycin + cefixime (pediatric) or levofloxacin/moxifloxacin (adult, when unable to take any beta-lactam).
5. Consider resistant organisms specifically — penicillin-resistant S. pneumoniae and beta-lactamase-producing H. influenzae — when selecting the next agent.
6. Refer to ENT for failure of second-line therapy, ≥4 episodes/year, anatomic anomalies, or any complication.

• Prescribing an antibiotic based on nasal discharge colour — this reflects neutrophils, not bacterial cause, and does not predict antibiotic benefit.
• Ordering a sinus x-ray or CT to "confirm" bacterial rhinosinusitis — imaging cannot distinguish viral from bacterial disease and is not recommended for uncomplicated cases.
• Framing antibiotics as necessary to prevent complications — complication rates are similar with or without antibiotic treatment.^[4]
• Reaching for amoxicillin/clavulanate as routine first-line therapy — amoxicillin alone is preferred by Canadian/AAO-HNSF experts given equivalent efficacy, lower cost, and fewer adverse effects, despite IDSA's differing recommendation.
• Using a macrolide (azithromycin, clarithromycin) as a routine alternative — inferior coverage of H. influenzae and S. pneumoniae, and higher resistance rates than amoxicillin.
• Continuing antibiotic therapy for a full extra week after symptoms resolve — short-course optimal-dose therapy (5-7 days in adults) is equally effective and causes fewer adverse effects.
• Labelling a nonspecific reaction as a penicillin "allergy" without clarifying true IgE-mediated status — this pushes patients toward less effective alternatives unnecessarily.
• Recommending an oral or topical decongestant, or systemic corticosteroid, based on an assumption of efficacy — none has RCT evidence of benefit in acute rhinosinusitis, and each carries its own real risks (rebound congestion, systemic decongestant effects, corticosteroid harms).

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Analgesics/antipyretics

Intranasal corticosteroids

Modest antibiotic-sparing benefit only (roughly 7 additional patients per 100 with marked improvement over placebo); high-dose regimens are needed, since low doses are no better than placebo. Maximal effect takes 7-14 days — not for immediate relief.

Nasal decongestants

No RCT evidence of efficacy specifically in acute rhinosinusitis. Limit topical use to 3-5 days — longer use causes rhinitis medicamentosa (rebound congestion). Efficacy/safety not well studied under 12 years; avoid oral decongestants under 6 years per Health Canada advisory.

Penicillins

First-line antibiotic class when treatment is indicated.

Tetracyclines

Preferred alternative for true penicillin allergy — excellent activity against rhinosinusitis pathogens, less resistance than macrolides, can be used regardless of age for short courses.

Cephalosporins

Lincosamides

Macrolides

Inferior coverage of H. influenzae and S. pneumoniae versus amoxicillin, and higher resistance rates — not routine alternatives. Reserve for patients unable to take a beta-lactam, particularly in pregnancy/breastfeeding.

Fluoroquinolones

Reserved for patients unable to take any beta-lactam, given broad spectrum, resistance potential, C. difficile risk, and persistent/disabling side effects (tendinopathy, peripheral neuropathy, neuropsychiatric effects). Health Canada and the FDA restrict use to patients with no alternative treatment options.