Respiratory Tract Infections

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URTIs - Sniffles & Sore Throats

URTIPathogen(s)Key SxComplications/Red Flags
Common ColdRhinovirusCoryza, mild sore throat2° infection (AOM, sinusitis)
PharyngitisViral; GAS (S. pyogenes)Sore throat, fever; GAS: exudatesRheumatic fever, PSGN; Peritonsillar abscess
Sinusitis (Ac.)Viral; S. pneumo, H. fluFacial pain, purulent dischargeOrbital cellulitis, meningitis
AOMS. pneumo, H. flu, M. catOtalgia, fever, bulging TMMastoiditis, meningitis
EpiglottitisH. flu b (↓); S. pneumo3D's: Dysphagia, Drooling, DistressAirway obstruction! (EMERGENCY)

S. pneumoniae: most common bacterial cause of AOM & acute bacterial sinusitis.

Pneumonias - Lung Inflamers Galore

PneumoniaLikely Pathogen(s)Key Clues / SxComplications / ⚠️ Red Flags
CAP - TypicalS. pneumoniae; H. flu, M. catSudden fever, rust sputum, lobar CXR shadowEmpyema, sepsis
CAP - AtypicalMycoplasma, Chlamydia, LegionellaDry cough, low-grade fever, GI / rash signsSevere hypoxemia, multi-organ failure
HAP / VAPPseudomonas, Klebsiella, MRSA≥48 h in hospital/vent, new infiltrateSeptic shock, MDR bugs
AspirationOral anaerobes; mixed GNBFoul sputum, RLL infiltrate, ↓GCS riskLung abscess, bronchopleural fistula
ImmunocompromisedPneumocystis (PCP), CMV, AspergillusSubacute dyspnea, “bat-wing” CXR (PCP)Pneumothorax (PCP), invasive aspergillosis
 0-1 → out-pt; 2 → ward; ≥3 → ICU.

S. pneumoniae remains the #1 cause of community-acquired pneumonia - and post-influenza bacterial pneumonia. ⭐ “Currant-jelly” sputum → think Klebsiella (alcoholics, diabetics).

Tuberculosis - India's Cough Scourge

CXR and CT showing apical cavitation in pulmonary TB

  • Pathogenesis & Types:
    • Primary TB: Ghon focus/complex (calcified lung lesion + hilar node). Often subclinical.
    • Post-Primary (Secondary) TB: Apical lung lesions, cavitation. Reactivation/reinfection. Symptoms: cough >2 wks, fever, night sweats, weight loss.
  • Diagnosis (NTEP):
    • Sputum Smear Microscopy (AFB).
    • CBNAAT/TrueNat: Initial test for all. Detects TB & Rif-resistance (<2 hrs).
    • Culture: LJ medium (4-8 wks), liquid culture (faster). Gold standard.
  • Treatment (DOTS - NTEP): 📌 RIPE (Rifampicin, Isoniazid, Pyrazinamide, Ethambutol)
    • New PTB: 2(HRZE) + 4(HRE).
    • Daily fixed-dose combinations (FDCs). Isoniazid: 5 mg/kg; Rifampicin: 10 mg/kg.

Cord factor (trehalose-6,6'-dimycolate) is a major virulence factor of M. tuberculosis, inhibiting phagosome-lysosome fusion and promoting granuloma formation.

Other LRTIs & Viruses - Viral Villains & Bronchial Banes

FeatureAcute BronchitisBronchiolitisPertussis (Whooping Cough)Influenza
EtiologyViral (Influenza, RSV)RSV (>50%), Adeno, ParainfluenzaBordetella pertussisInfluenza A, B (Orthomyxovirus)
Age GroupAdults< 2 yrs (peak 3-6 mo)< 1 yr (unvax), adolescentsAll ages
Key ClinicalCough (±sputum), wheeze; no pneumoniaURI → resp distress, wheeze, apnea📌 CPC: Catarrhal, Paroxysmal (whoop), ConvalescentAbrupt fever, myalgia, cough, headache
ManagementSymptomatic; bronchodilators if wheezeSupportive (O2, fluids); Ribavirin (severe)Macrolides (Azithro); supportive careOseltamivir/Zanamivir (early, high-risk)

⭐ RSV is the most common cause of bronchiolitis in infants, often leading to hospitalization in this age group globally and in India.

High‑Yield Points - ⚡ Biggest Takeaways

  • Streptococcus pneumoniae is the most common cause of Community-Acquired Pneumonia (CAP).
  • Atypical pneumonia: think Mycoplasma (cold agglutinins), Legionella (hyponatremia, ↑LFTs, GI symptoms).
  • Klebsiella pneumoniae causes currant jelly sputum, especially in alcoholics and diabetics.
  • Haemophilus influenzae causes epiglottitis (thumb sign) and pneumonia in COPD patients.
  • Pseudomonas aeruginosa is linked to HAP, VAP, and cystic fibrosis exacerbations.
  • TB diagnosis: sputum AFB/NAAT (CBNAAT); CXR shows apical lesions/cavitation.

Practice Questions: Respiratory Tract Infections

Test your understanding with these related questions

A 6-month-old female infant is brought to the physician with a 2-day history of severe cough, wheezing, and respiratory distress. Physical examination shows rhinitis, mild cyanosis, and fever. Which of the following is the most likely etiology of this child's pulmonary infection?

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Flashcards: Respiratory Tract Infections

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The bugs that are associated with Guillain-Barre Syndrome are ICE MyCZ:I_____CMVEBVMycoplasma PneumoniaeCampylobacterZika

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The bugs that are associated with Guillain-Barre Syndrome are ICE MyCZ:I_____CMVEBVMycoplasma PneumoniaeCampylobacterZika

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