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MI7.{1,4} | Upper Respiratory Tract Infections — SDL Guide (Part 2)

Viral URTIs

A five-panel infographic compares major viral upper respiratory tract infections, showing rhinovirus, EBV mononucleosis, influenza, and adenovirus with key receptors, clinical features, diagnostics, and prevention points. — **Panel A:** Upper respiratory tract overview showing nasopharyngeal epithelium, oropharynx, tonsils, cervical lymph nodes, spleen icon, and lower respiratory extension for influenza involvement.. **Panel B:** Common cold due to Rhinovirus showing viral attachment to ICAM-1 receptors on nasopharyngeal epithelium, many serotypes, self-limited illness, and antibiotics contraindicated.. **Panel C:** Infectious mononucleosis due to EBV showing EBV binding CD21/CR2 on B lymphocytes, exudative pharyngitis, generalized lymphadenopathy, splenomegaly, Downey cells, heterophile antibody testing, EBV serology, and ampicillin rash warning.. **Panel D:** Influenza showing Orthomyxovirus with segmented negative-sense ssRNA, HA binding sialic acid, NA-mediated virion release, antigenic drift, antigenic shift, nasopharyngeal swab testing, RT-PCR confirmation, and inactivated vaccine.. **Panel E:** Adenovirus showing non-enveloped dsDNA virus with pharyngo-conjunctival fever in children and epidemic keratoconjunctivitis..

Common cold (Rhinovirus):
- Over 160 serotypes → no vaccine possible
- Binds ICAM-1 receptor on nasopharyngeal epithelium
- Self-limited; antibiotics contraindicated

Infectious Mononucleosis (EBV):
- Epstein–Barr virus (HHV-4), dsDNA, Herpesviridae
- Triad: fever, severe pharyngitis with exudate, generalised lymphadenopathy + splenomegaly
- EBV infects B lymphocytes via CD21 (CR2) receptor
- Atypical lymphocytes (Downey cells) on peripheral blood smear
- Paul–Bunnell / Monospot test — detects heterophile antibodies (IgM agglutinating sheep/horse RBCs)
- Specific: Anti-VCA IgM (acute), Anti-EA, Anti-EBNA
- Avoid ampicillin (causes maculopapular rash in EBV mononucleosis)

Influenza (seasonal):
- Orthomyxovirus; segmented negative-sense ssRNA
- Infects upper AND lower respiratory epithelium
- Haemagglutinin (HA) binds sialic acid receptors; Neuraminidase (NA) enables virion release
- Antigenic drift (mutations) → seasonal epidemics; Antigenic shift (reassortment) → pandemic
- Rapid antigen test (nasopharyngeal swab); RT-PCR for confirmation
- Vaccines: trivalent/quadrivalent inactivated (recommended for healthcare workers in India)

Adenovirus:
- Non-enveloped dsDNA; pharyngo-conjunctival fever in children; epidemic keratoconjunctivitis

Fungal and Parasitic URTIs

A three-panel medical diagram comparing oral candidiasis, rhinocerebral mucormycosis, and rhinosporidiosis with clinical signs, microscopy findings, risk factors, and an otitis media clinical pearl. — **Panel A:** Open mouth showing buccal mucosa, tongue, pharynx, white removable plaques, erythematous mucosa beneath plaque, KOH inset with budding yeast cells and pseudohyphae, Candida albicans label, risk factors: antibiotics, inhaled corticosteroids, diabetes, HIV/immunosuppression, treatment: topical nystatin or fluconazole in HIV-associated oropharyngeal candidiasis. **Panel B:** Sagittal head showing nasal cavity, paranasal sinuses, orbit, brain, red arrows showing sinus-to-orbit-to-brain spread, Rhizopus/Mucor/Cunninghamella label, risk factors: uncontrolled diabetes/DKA and post-COVID immunosuppression, microscopy inset with broad aseptate ribbon-like hyphae branching at 90 degrees, treatment: liposomal amphotericin B plus surgical debridement. **Panel C:** Frontal nasal cavity showing polypoid nasal lesion, Rhinosporidium seeberi label, endemic region note: south India and Sri Lanka, histology inset with large sporangia containing endospores, note that parasitic URTIs are rare in immunocompetent hosts. **Clinical pearl strip:** Child ear icon, tympanic membrane, otitis media complication note, bacterial causes: Streptococcus pneumoniae, non-typeable Haemophilus influenzae, Moraxella catarrhalis, reminder to examine tympanic membrane in febrile child with URI.

Oral candidiasis (thrush):
- Candida albicans — dimorphic fungus, forms pseudohyphae and chlamydospores
- White removable plaques on buccal mucosa/tongue/pharynx
- Risk factors: broad-spectrum antibiotics, corticosteroid inhalers, diabetes, HIV/immunosuppression
- KOH mount: pseudohyphae + budding yeast cells
- Treatment: topical nystatin; fluconazole for oropharyngeal candidiasis in HIV

Rhinocerebral Mucormycosis:
- Rhizopus, Mucor, Cunninghamella — angioinvasive mould; wide aseptate hyphae at right angles
- Sinuses → orbit → brain; very high mortality
- Risk factors: uncontrolled diabetes (especially DKA), post-COVID immunosuppression (Black Fungus epidemic in India, 2021)
- LPCB/H&E: broad, aseptate, ribbon-like hyphae branching at 90°
- Treatment: liposomal amphotericin B + surgical debridement

Parasitic URTIs are rare in immunocompetent hosts. Rhinosporidiosis (nasal polyps caused by Rhinosporidium seeberi — a protist) is endemic in south India and Sri Lanka; diagnosed by histology showing large sporangia.

CLINICAL PEARL

Otitis media is the commonest complication of viral URI in children. S. pneumoniae (30–40%), H. influenzae non-typeable (25%), and M. catarrhalis (15%) are the major bacterial causes. PCV13 vaccine (part of UIP from 2017 in select states) significantly reduces pneumococcal otitis media. Always examine the tympanic membrane in a febrile child with URI.

Specimen Collection and Processing for URTIs (MI7.4 practical focus)

A four-panel microbiology practical diagram shows correct throat swab collection sites, transport conditions, common smear stain findings, and clinical correlation for upper respiratory tract infections. — **Panel A:** Open mouth, elevated uvula, tonsillar pillars, posterior pharyngeal wall, sterile cotton/Dacron swab, tongue depressor, avoid tongue, avoid buccal mucosa, correct swab path across both tonsillar pillars and posterior pharynx.. **Panel B:** Sterile swab, Stuart's transport medium, Amies medium alternative, transport within 2 hours, microbiology laboratory, refrigerate at 4°C if delay exceeds 2 hours.. **Panel C:** Gram stain: Gram-positive cocci in chains, GAS; Albert stain: C. diphtheriae bacilli with blue-black metachromatic granules; KOH mount: Candida pseudohyphae and budding yeast.. **Panel D:** Exudative tonsillitis plus Gram-positive cocci in chains leads to culture for GAS; suspected diphtheria plus metachromatic granules leads to urgent diphtheria workup..

Throat swab technique:
1. Ask patient to say 'Aah' — uvula rises, exposing tonsillar pillars
2. Use a sterile cotton/Dacron swab; avoid tongue and buccal mucosa
3. Swab both tonsillar pillars and posterior pharynx
4. Transport in Stuart's transport medium within 2 hours (or Amies medium)
5. Refrigerate at 4°C if delay >2 hours

Stains performed on throat swab smear:

Stain	Target	Appearance	Purpose
Gram stain	GAS, other bacteria	Gram+ve cocci in chains (GAS)	Screening
Albert stain	C. diphtheriae	Blue-black granules in yellowish-green bacilli	Diphtheria
KOH mount	Candida	Pseudohyphae + budding yeast	Oral candidiasis

Correlating smear with clinical findings:
- Gram stain: Gram+ve cocci in chains + exudative tonsillitis → culture for GAS
- Albert stain: metachromatic granules + pseudomembrane → initiate DAT, confirm with Elek's
- No organisms on Gram stain + prominent lymphadenopathy → consider EBV (Paul-Bunnell test)

SELF-CHECK

A 30-year-old healthcare worker develops fever, severe sore throat and petechiae on the palate. Peripheral blood smear shows atypical lymphocytes. The MOST appropriate next investigation is:

A. Throat culture on blood agar

B. Albert stain of throat swab

C. Paul-Bunnell / Monospot test

D. ASO titre

Reveal Answer

Answer: C. Paul-Bunnell / Monospot test

The clinical picture — exudative tonsillitis, palatal petechiae, atypical lymphocytes (Downey cells) — is classic for Infectious Mononucleosis caused by EBV. The Paul-Bunnell (Monospot) test detects heterophile antibodies and is the rapid bedside test of choice. ASO titre detects past GAS infection; Albert stain is for diphtheria; throat culture would be done but is not the most specific next step here.

Interactive practice: Flip Cards

Interactive practice: Multiple Choice

Interactive practice: True / False

Interactive practice: Put in Order