Acute bacterial rhinosinusitis — fellow's quick read

Personal study digest for a new ID fellow. Recommendations are drawn from the IDSA 2012 ABRS guideline (Chow et al) and the AAO-HNS 2025 Adult Sinusitis Update. The “What’s changed since 2012” section is reviewer synthesis of newer evidence, each claim cited. Not a substitute for the full guideline.

In one line

Most acute rhinosinusitis is viral — only ~2–10% is bacterial. Diagnose ABRS by time-course, not imaging (persistent ≥10 d, severe ≥3–4 d, or “double-worsening”), then either watchful-wait or give amoxicillin ± clavulanate — not a fluoroquinolone.

◆When to suspect / diagnose

ABRS is a clinical diagnosis — no imaging, no routine cultures. Suspect bacterial when any one of three time-courses is met (IDSA rec 1, strong; AAO-HNS KAS 1):
- Persistent — symptoms ≥10 days without improvement.
- Severe — fever ≥39°C (102°F) and purulent discharge or facial pain, ≥3–4 consecutive days at onset.
- “Double-worsening” — new fever, headache, or increased discharge after a viral URI (5–6 d) that was already improving.
Viral rhinosinusitis: <10 days and not worsening (AAO-HNS). The first 3–4 days cannot distinguish viral from early ABRS.
Bacterial disease is the minority, and ~70% of ABRS improves without antibiotics in placebo trials — over-diagnosis drives the ~81% antibiotic-prescribing rate in adults (IDSA).

◆Workup the fellow drives

Do not image uncomplicated ABRS. Plain films, CT, and MRI are abnormal in most viral URIs and cannot separate viral from bacterial (IDSA rec 24; AAO-HNS). A normal CT rules ABRS out; an abnormal one does not rule it in.
Reserve contrast CT (axial + coronal) for suspected orbital or intracranial extension — severe headache, proptosis, cranial-nerve palsy, facial swelling, vision change (IDSA rec 24).
Never rely on a nasopharyngeal swab — unreliable for ABRS (IDSA rec 23, strong/high). If therapy fails, sample by direct sinus aspiration (rec 21) or endoscopic middle-meatus culture (rec 22).

◆Empiric & definitive therapy

Scenario	Drug / dose / route	Notes
First-line (adult)	Amoxicillin-clavulanate 875/125 mg PO BID (or 500/125 mg PO TID)	β-lactam preferred over fluoroquinolone (IDSA rec 6). AAO-HNS 2025: amoxicillin ± clavulanate both acceptable.
High-dose (adult)	Amoxicillin-clavulanate 2000/125 mg PO BID	Resistance risk: severe illness, age <2 or >65, daycare, antibiotics/hospitalization in past month, immunocompromised, or region ≥10% penicillin-nonsusceptible pneumococcus (rec 5).
Penicillin allergy (adult)	Doxycycline 100 mg PO BID (or 200 mg PO daily)	Preferred alternative — keeps pneumococcal + H. influenzae activity (rec 9, 11).
Reserve / last resort	Levofloxacin 500 mg PO daily or moxifloxacin 400 mg PO daily	Fluoroquinolones only when no alternative — FDA 2016 boxed warning (see below).
Not recommended	Macrolides; TMP-SMX; oral cephalosporin monotherapy	Pneumococcal resistance ~30% (macrolide), ~30–40% (TMP-SMX) (rec 7, 8, 10).
Children	Amoxicillin-clavulanate 45 mg/kg/day (standard) or 90 mg/kg/day (high-dose) PO BID	Amox-clav preferred over amoxicillin (strong, rec 3); severe/hospitalized → IV ampicillin-sulbactam 200–400 mg/kg/day q6h.

◆Duration & stopping

Adults, uncomplicated: 5–7 days (IDSA rec 14; AAO-HNS 2025, down from 5–10). Children: 10–14 days (rec 15).
Watchful waiting — for uncomplicated ABRS, offer delayed antibiotics (up to 5 days after diagnosis) with assured follow-up. AAO-HNS 2025 extends this to all severities. (IDSA 2012 instead says treat once ABRS is diagnosed — an honest society divergence.)
Switch agent if symptoms worsen at 48–72 h or fail to improve by 3–5 days (IDSA rec 19). Reassess to confirm ABRS, exclude other causes, and detect complications.

◆Special populations & adjuncts

Penicillin allergy — verify it; most labeled patients tolerate amoxicillin. True allergy: doxycycline (adults). Children: type-I → levofloxacin; non-type-I → clindamycin + cefixime or cefpodoxime (rec 12).
No routine S. aureus / MRSA coverage in initial empiric therapy (rec 13, strong).
Adjuncts: intranasal saline irrigation (rec 16) and intranasal corticosteroids — mainly with an allergic-rhinitis history (rec 17). Decongestants and antihistamines are not recommended (rec 18).

◆Key decisions a fellow owns

Bacterial vs viral by time-course, not imaging — this is the whole game; getting it right is the main lever against over-prescription.
Watchful waiting vs immediate antibiotics — appropriate for any uncomplicated ABRS when follow-up is assured.
Reach for doxycycline, not a fluoroquinolone, in penicillin allergy.
Escalate for complications — orbital/intracranial signs → contrast CT + ENT/ID; recurrent, refractory, or immunocompromised → specialist referral (rec 25).

What’s changed since 2012

Reviewer synthesis of newer evidence — not the guideline. Each claim cited; flags where the 2012 IDSA guideline lags current practice.

IDSA has not updated — the 2012 guideline is still the operative IDSA reference (no newer version). AAO-HNS 2025 is the current US society update. idsociety.org; AAO-HNS 2025, doi:10.1002/ohn.1344 (exec summary PMID 40741969)
Watchful waiting now for ALL uncomplicated ABRS — AAO-HNS 2025 extends delayed antibiotics (up to 5 days) to every severity, not just “mild” illness. AAO-HNS 2025, doi:10.1002/ohn.1344
Fluoroquinolones demoted — FDA (26 Jul 2016) reserves them for acute bacterial sinusitis only when no alternative exists, with a boxed warning for disabling/potentially permanent tendon, joint, nerve, and CNS effects. AAO-HNS 2025 dropped fluoroquinolones for penicillin allergy; doxycycline is the preferred alternative — reversing IDSA 2012 rec 11. FDA Drug Safety Communication, 26 Jul 2016
Antibiotics help only marginally — Cochrane 2018 (15 RCTs, 3057 adults): ~½ cured at 1 week and ⅔ by 14 days without antibiotics; only 5/100 (clinical dx) to 11/100 (imaging) more cured faster, at a cost of 13/100 more adverse effects (NNTB ~19 vs NNTH ~8). Grounds watchful waiting. Lemiengre, Cochrane 2018; PMID 30198548, doi:10.1002/14651858.CD006089.pub5
Plain amoxicillin acceptable again — AAO-HNS 2025 makes clavulanate optional (clinician discretion) on stewardship grounds; IDSA 2012 still prefers amox-clav for the β-lactamase–producing H. influenzae / M. catarrhalis that predominate after pneumococcal conjugate vaccination. AAO-HNS 2025; IDSA 2012 rec 3–4
No clinical rule reliably finds bacterial disease — primary-care diagnostic meta-analyses show no single sign, symptom, or blood test confirms ABRS, and no subgroup gains large antibiotic benefit; the ≥10-day / double-worsening criteria are pragmatic, not proven bacterial-specific. PMID 33148765 (2020); PMID 34210729 (2021)

◆Anki cards minted this run

Watchful waiting for all uncomplicated ABRS regardless of severity (AAO-HNS 2025).
Penicillin allergy → doxycycline preferred; fluoroquinolone reserved (FDA 2016 boxed warning) — reverses IDSA 2012.
High-dose amoxicillin-clavulanate 2000/125 mg PO BID and its resistance-risk indications.
Duration: adults 5–7 days vs children 10–14 days; switch if worse at 48–72 h or not improving by 3–5 days.

Anki MCP was unreachable this run — the 4 cards are staged as a TSV for import and still need a live dedup against the deck.

Sources: IDSA ABRS guideline 2012 (Chow et al, Clin Infect Dis 2012;54(8):e72–e112, doi:10.1093/cid/cis370); AAO-HNS Adult Sinusitis Update 2025 (Payne et al, Otolaryngol Head Neck Surg 2025;173(S1):S1–S56, doi:10.1002/ohn.1344; executive summary PMID 40741969); FDA Drug Safety Communication on fluoroquinolones, 26 Jul 2016; Cochrane review of antibiotics for acute rhinosinusitis in adults 2018 (PMID 30198548, doi:10.1002/14651858.CD006089.pub5); primary-care diagnostic meta-analyses (PMID 33148765; PMID 34210729).