M11.1: Acute Upper Respiratory Infections

Learning Objectives

• Differentiate upper respiratory tract infections (URTI) from lower respiratory tract infections (LRTI)
• Apply clinical decision rules (McIsaac score) to guide appropriate antibiotic use in sore throat
• Recognize and manage common viral syndromes: measles, varicella, HFMD, mononucleosis
• Identify URTI mimics endemic to Singapore: dengue, chikungunya, zika
• Manage COVID-19 and influenza with current MOH/CDC guidelines
• Treat site-specific URTIs: pharyngitis, laryngitis, sinusitis, otitis media

Clinical Approach to URTI

• URTIs are common in primary care; usually present with cough, sore throat, runny nose, fever, body aches
• Key task: differentiate URTI from LRTI and identify need for antibiotics
• URTI symptoms may herald serious illness (SARS 2003, COVID-19 pandemic)
• Three clinical approaches: (1) Rule out non-infective causes, (2) Ascertain epidemiological contact, (3) Exclude LRTI

Spectrum of Infections in URTI

• Non-specific URTI: initial picture may evolve into unique viral syndrome or site-specific bacterial infection
• Unique viral syndromes: pathognomonic features confirm diagnosis (e.g., rash in measles or varicella)
• Site-specific URTI: localized infection (tonsillitis, pharyngitis, laryngitis, sinusitis, otitis media)
• Influenza-like illness (ILI): non-specific presentation; shared by many viral pathogens

Antibiotic Use in URTI: ICE Framework

• Generally NOT indicated: unique viral syndromes, non-specific URTI, certain viral site-specific URTIs
• Always address patient's Ideas, Concerns, and Expectations (ICE)
• If antibiotics unclear: use clinical judgment; consider age, comorbidities, toxicity, immunocompromise
• If patient demands antibiotics but not indicated: explain reasoning; consider safety-net or delayed prescription
• Communication reduces unnecessary prescribing driven by perceived patient expectations

Acute Coryza (Common Cold)

• Mild, self-limiting: runny nose, sneezing, watery eyes, mild sore throat, minimal constitutional symptoms
• Pathogens: Coronaviruses, Adenoviruses, Rhinoviruses, RSV, Parainfluenza, Influenza
• Spread: respiratory droplets and contact with mucous secretions; incubation 1–3 days
• Symptoms resolve within 1–2 weeks; cough from post-nasal drip common; fever usually <38°C
• Muco-purulent rhinitis is NOT an indication for antibiotics without other signs of bacterial sinusitis

Influenza: Pathogen & Prevention

• Influenza A and B: historical pandemics; continue seasonal outbreaks
• Vaccine updated biannually (Northern/Southern Hemisphere versions) to match circulating strains
• Immunity develops ~2 weeks post-vaccination; protection lasts months to year
• Vaccination recommended before Singapore influenza seasons: Dec–Feb and May–July

Influenza: Clinical Presentation & Diagnosis

• Clinical Pearl: abrupt onset of systemic symptoms (fever, malaise, arthralgia, myalgia) followed by URTI symptoms (dry cough, sore throat); lasts 3–7 days
• Diagnosis often clinical; testing reserved for hospitalised, severe, or outbreak management
• Rapid Influenza Diagnostic Tests (RIDTs): sensitivity 10–70%, specificity >95%; negative does NOT exclude influenza
• RT-PCR is gold standard; point-of-care molecular tests (rapid PCR) offer near-PCR sensitivity with faster turnaround

Influenza: Antiviral Therapy — Current CDC Guidance

• Initiate as soon as possible — ideally within 48 hours of symptom onset
• Indicated: hospitalised patients, severe/progressive illness, high-risk complications
• Treatment beyond 48 hours may still benefit hospitalised or high-risk patients
• Chemoprophylaxis: consider for high-risk with close contact during infectious period; avoid in healthy individuals or contact >48 hours prior

Infectious Mononucleosis (IM)

• Cause: Epstein-Barr virus (HHV-4), rarely Cytomegalovirus (HHV-5)
• Transmission: saliva ('kissing disease')
• Clinical Pearl: IM is a SYSTEMIC infection with throat manifestations; streptococcal pharyngitis is local
• Key differentiator: suspect IM in adolescent/young adult with severe sore throat, exudative tonsillitis, posterior cervical lymphadenopathy, fatigue, periorbital edema

Vector-Borne URTI Mimics: Dengue Overview

• Singapore's tropical climate and high mosquito population make dengue, chikungunya, and zika endemic URTI mimics
• Dengue: acute onset fever, headache, backache, myalgia, rash, retro-orbital pain; three phases: febrile, critical, recovery
• Distinguish from typical URTI: look for severe systemic symptoms, rash, warning signs (persistent vomiting, severe abdominal pain, mucosal bleeding)
• Statutory notification required; supportive care with careful fluid management; avoid NSAIDs and contact sports during critical phase

Chikungunya & Zika

• 💎 Chikungunya: fever + SEVERE, debilitating polyarthralgia/polyarthritis; rash common; differentiate from typical URTI by joint involvement
• Zika: mild URTI-like symptoms (rash, joint pain, conjunctivitis) but associated with Guillain-Barré syndrome (adults) and congenital microcephaly (maternal infection)
• Prevention (all vector-borne): DEET-containing repellent, long clothing, eliminate stagnant water
• Zika in pregnancy: avoid travel to affected areas; counsel on contraception if planning pregnancy

COVID-19: Pathogen, Transmission & Complications

• Caused by SARS-CoV-2; asymptomatic spread and airborne transmission drive high infectivity
• Symptoms: highly variable — non-specific URTI (sore throat, cough, headache, fatigue) to severe respiratory distress
• Anosmia/ageusia: classic with early variants but less prominent in Omicron sub-lineages
• Complications: acute (cardiovascular events, thrombosis, AKI) and chronic (Long COVID — fatigue, dyspnea, cognitive dysfunction)
• Vaccination before infection appears to reduce Long COVID risk

COVID-19: Oral Antivirals & Indications

• Indicated: mild-to-moderate disease in HIGH-RISK patients if started within 5 days of symptom onset
• High-risk factors: not up-to-date with vaccination, age >60–70, active cancer, chronic kidney/lung/heart disease, obesity, diabetes, immunosuppression
• Nirmatrelvir/ritonavir (Paxlovid): preferred; dose adjust for GFR 30–60; contraindicated GFR <30 or severe hepatic impairment; note CYP3A4 interactions
• Molnupiravir/Ensitrelvir: alternatives; molnupiravir NOT in pregnancy or women unable to use contraception

COVID-19 Vaccination (MOH Singapore 2025–2026)

• Additional dose recommended at ~1 year (minimum 5 months) from last vaccine dose
• Recommended for: age ≥60 years, medically vulnerable ≥6 months, aged care residents
• Immunocompromised individuals may need more frequent dosing — refer to current MOH/NCID guidance
• Vaccines available: Pfizer-BioNTech, Moderna, Novavax, Sinovac-CoronaVac (targeting Omicron sub-lineages)
• Vaccination reduces severe disease, hospitalization, and death; may reduce Long COVID risk

Site-Specific URTI: Acute Sore Throat (Pharyngitis)

• Most sore throats are viral and self-limiting; challenge is identifying Group A Beta-Haemolytic Streptococcus (GABHS)
• GABHS causes only 5–15% of adult pharyngitis but can lead to acute rheumatic fever (especially in children)
• Use McIsaac clinical score to predict GABHS likelihood and guide testing/treatment decisions
• Clinical Pearl: viral features (cough, coryza, conjunctivitis, diarrhea, hoarseness, oral ulcers) suggest viral; bacterial features (abrupt onset, fever, exudates, tender cervical nodes, absence of cough) suggest GABHS

Epiglottitis: A Medical Emergency

Acute Laryngitis

• Typically viral; presents with hoarseness, aphonia, dry cough
• Mainstay of treatment: voice rest and hydration
• Antibiotics generally NOT indicated (no benefit over supportive care alone)
• If bacterial cause strongly suspected, macrolides (e.g., erythromycin) have been suggested but evidence limited

Acute Sinusitis: Overview & Diagnosis

• Most cases are viral; bacterial infection suspected if symptoms persist >10 days, severe from onset, or worsen after initial improvement ('double sickening')
• Clinical predictors of ACUTE BACTERIAL SINUSITIS: maxillary toothache, purulent nasal secretion, poor response to decongestants, abnormal transillumination, coloured discharge
• ≥4 predictors = high probability (LR 6.4); 2–3 predictors = intermediate (LR 2.6); ≤1 predictor = low probability (LR 0.5)

Acute Sinusitis: Management & Antibiotics

• Initial therapy for uncomplicated cases: watchful waiting + symptomatic treatment (analgesics, saline irrigation) for 1 week
• Antibiotics (5–7 day course) if indicated: amoxicillin-clavulanate (500/125 mg TDS or 875/125 mg BD) first-line
• For penicillin allergy: doxycycline 100 mg BD or respiratory fluoroquinolone (levofloxacin 500 mg OD or moxifloxacin 400 mg OD)
• Referral indicated: severe symptoms, failure to respond to antibiotics, suspected complications (orbital cellulitis, meningitis, cavernous sinus thrombosis)

Otitis Media: AOM vs OME

• Acute Otitis Media (AOM): middle ear fluid + acute signs of inflammation (otalgia, fever, bulging/red TM)
• Otitis Media with Effusion (OME): middle ear fluid WITHOUT acute signs of infection ('glue ear')
• AOM management: analgesia (paracetamol/ibuprofen) ± observation period (48–72 hours for age ≥2 years, non-severe, unilateral)
• OME management: watchful waiting; spontaneous resolution in ~75% within 3 months; refer to ENT if persistent >3 months with hearing loss