Respiratory infection from Harrison of internal medicine

Reading File

Finding Sources

Reading File

I now have rich content from Harrison's. Let me compile a comprehensive overview of respiratory infections.

Respiratory Infections — Harrison's Principles of Internal Medicine, 22nd Edition (2025)

1. NONSPECIFIC UPPER RESPIRATORY INFECTION ("The Common Cold")

Definition & Etiology

A respiratory tract infection where no single symptom predominates. Transmitted via direct contact with infected individuals, contaminated surfaces, and respiratory droplets.

Common causative viruses:

Rhinoviruses (>100 serotypes) — most common
Coronaviruses (non-COVID)
Parainfluenza virus
Respiratory syncytial virus (RSV)
Influenza virus
Adenovirus (57 serotypes)
Metapneumovirus
Bocavirus

Specific viral diagnosis is not practical or necessary. Multiplex RT-PCR panels exist but may be overly sensitive. Differential includes influenza, measles (cough + coryza + conjunctivitis), acute HIV (sore throat + rash), and COVID-19.

Symptoms & Signs

Incubation: 2–8 days
Nasal fullness/obstruction, rhinorrhea, sore throat, laryngitis, lymphadenopathy, cough, low-grade fever
Myalgias less prominent than in influenza
Epistaxis with frequent nose-blowing
Physical exam: conjunctivitis, pharyngeal erythema/exudates/cobblestoning; nasal mucosa may be pale, boggy, or red; nasal mucus watery to purulent; lungs may show diffuse wheezing or bronchial breath sounds
Duration: usually 5–10 days, up to 14 days

Treatment

Adults and older children — symptom-based:

Symptom	Treatment
Fever/myalgias/sore throat	Acetaminophen or NSAIDs (e.g., ibuprofen)
Rhinorrhea	Ipratropium bromide
Nasal congestion	Oxymetazoline (2 sprays each nostril BID, ≤5 days) or pseudoephedrine
Cough	Dextromethorphan or benzonatate (Tessalon Perles)

Children <6 years: Cough/cold medicines are contraindicated due to adverse effects. Honey (for children >1 year) soothes sore throat. Cool-mist humidifiers may help breathing.

2. ACUTE SINUSITIS

Etiology

Most cases are viral (rhinovirus, parainfluenza, adenovirus). Bacterial superinfection occurs in ~2% of cases. The most common bacterial pathogens are:

Streptococcus pneumoniae
Haemophilus influenzae
Moraxella catarrhalis

Clinical Features

Facial pain/pressure, nasal obstruction, purulent nasal discharge, anosmia
Symptoms >10 days, or worsening after initial improvement ("double-sickening") suggest bacterial sinusitis
Severe symptoms (high fever, periorbital edema, severe headache) warrant urgent evaluation for complications (orbital or intracranial extension)

Treatment — Acute Sinusitis

Viral: Symptomatic — decongestants, saline irrigation, analgesics
Bacterial (mild–moderate): Amoxicillin-clavulanate is first-line; doxycycline or fluoroquinolone if penicillin-allergic
Duration: 5–7 days for mild; 10–14 days for severe or complicated

Chronic Sinusitis

Defined as symptoms lasting >12 weeks. Often involves mixed bacterial flora, biofilms, and underlying contributors (allergies, nasal polyps, immunodeficiency). Management includes intranasal steroids, saline irrigation, and surgical referral (functional endoscopic sinus surgery) for refractory cases.

3. PHARYNGITIS

Streptococcal Pharyngitis (GAS — Group A Streptococcus)

Etiology: Streptococcus pyogenes (Group A β-hemolytic streptococcus)

Clinical Features (Centor/McIsaac criteria):

Tonsillar exudates
Tender anterior cervical lymphadenopathy
Fever
Absence of cough

Diagnosis: Rapid strep antigen test; throat culture if rapid test negative in high-suspicion cases.

Treatment:

Penicillin V or amoxicillin × 10 days (first-line)
Amoxicillin-clavulanate for recurrent cases
Azithromycin or clindamycin if penicillin-allergic

Goals of treatment: Prevent acute rheumatic fever, suppress suppurative complications (peritonsillar abscess, retropharyngeal abscess), reduce symptom duration.

Nonstreptococcal Pharyngitis

Causes include:

Infectious mononucleosis (EBV): sore throat, exudative tonsillitis, cervical lymphadenopathy, splenomegaly, fatigue — avoid amoxicillin/ampicillin (causes rash)
Adenovirus, HSV, CMV, HIV (acute infection)
Fusobacterium necrophorum (Lemierre's syndrome risk)
Arcanobacterium haemolyticum: pharyngitis + scarlatiniform rash in young adults

4. OTITIS (Ear Infections in the Context of Respiratory Infections)

Otitis Externa ("Swimmer's Ear")

Pathogens: Pseudomonas aeruginosa, Staphylococcus aureus; fungi (Aspergillus, Candida) cause pruritic form
Risk factors: Swimming, cotton swab trauma, narrow ear canals, eczema
Exam: Pain on movement of auricle/tragus; edematous, erythematous canal
Treatment: Topical antibiotic/steroid drops (ciprofloxacin + hydrocortisone); keep canal dry
Malignant otitis externa: Life-threatening form in diabetics/immunocompromised; involves temporal bone; can affect cranial nerves VII, IX, XI, XII → requires IV antipseudomonal antibiotics

5. PNEUMONIA

Definition

Infection of the pulmonary parenchyma. Classified as:

Community-Acquired Pneumonia (CAP)
Hospital-Acquired Pneumonia (HAP)
Ventilator-Associated Pneumonia (VAP)
(Healthcare-associated pneumonia as a separate category is no longer recommended)

Community-Acquired Pneumonia (CAP)

Pathophysiology: Microaspiration of oropharyngeal organisms is the primary mechanism. Inflammatory cascade involving IL-6, TNF (fever), IL-8, G-CSF (neutrophil recruitment) leads to alveolar consolidation.

Common Pathogens:

Type	Organisms
Typical bacteria	S. pneumoniae (most common), H. influenzae, Moraxella catarrhalis
Atypical	Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila
Viral	Influenza, SARS-CoV-2, RSV, adenovirus

Clinical Features:

Fever, cough (productive or dry), dyspnea, pleuritic chest pain
Lobar consolidation on exam: dullness to percussion, bronchial breath sounds, egophony
CXR: lobar consolidation, interstitial infiltrates, or patchy opacification

Severity Assessment — PSI / CURB-65: CURB-65 (1 point each): Confusion, Urea >7 mmol/L, Respiratory rate ≥30, BP <90/60 mmHg, age ≥65

Score 0–1: Outpatient
Score 2: Consider hospitalization
Score ≥3: Hospitalize; ≥4–5: consider ICU

Empirical Antibiotic Treatment of CAP:

Setting	Regimen
Outpatient, no comorbidities	Amoxicillin 1 g TID × 5 days or doxycycline 100 mg BID × 5 days
Outpatient, with comorbidities	Amoxicillin-clavulanate + macrolide, or respiratory fluoroquinolone (levofloxacin 750 mg/d, moxifloxacin)
Inpatient, non-ICU	β-lactam + macrolide (azithromycin/clarithromycin), or respiratory fluoroquinolone
ICU	β-lactam (ceftriaxone/ampicillin-sulbactam) + azithromycin or fluoroquinolone; add anti-MRSA agent if risk factors

Aspiration pneumonia: ~5–15% of CAP; involves right lower lobe (or posterior segment of right upper lobe); polymicrobial — anaerobes + gram-negatives; treat with amoxicillin-clavulanate or clindamycin ± a gram-negative agent.

Hospital-Acquired Pneumonia (HAP) & Ventilator-Associated Pneumonia (VAP)

Definition:

HAP: Pneumonia occurring ≥48 hours after hospital admission, not incubating at admission
VAP: Pneumonia occurring ≥48–72 hours after endotracheal intubation

Pathogens: Gram-negatives dominate — Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, Enterobacterales; also MRSA. Atypical organisms rare (except Legionella in nosocomial outbreaks from water systems).

MDR Risk Factors: Prior antibiotics, prior hospitalization, known MRSA colonization, chronic hemodialysis, high local MRSA rates.

Empirical Treatment of HAP/VAP:

Risk Category	Regimen
No MDR risk factors	Piperacillin-tazobactam 4.5 g IV q6h or cefepime 2 g IV q8h or levofloxacin 750 mg IV q24h
MDR gram-negative risk	Two gram-negative agents: antipseudomonal β-lactam + aminoglycoside (amikacin 15–20 mg/kg q24h, gentamicin, tobramycin) or fluoroquinolone
Add if MRSA risk	Linezolid 600 mg IV q12h or vancomycin (trough 15–20 mg/dL)
Resistant gram-negatives (CRE, metallo-β-lactamase)	Newer agents: ceftazidime-avibactam, ceftolozane-tazobactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, sulbactam-durlobactam

De-escalation: Adjust antibiotics based on culture results and clinical response. Duration typically 7–8 days unless organism or clinical response dictates otherwise.

Summary Table: Respiratory Infections at a Glance

Condition	Key Pathogens	Hallmark Features	First-Line Treatment
Common cold	Rhinovirus, coronavirus	Rhinorrhea, low-grade fever, 5–14 days	Symptomatic only
Acute sinusitis (bacterial)	S. pneumoniae, H. influenzae	Facial pain, purulent discharge >10 days	Amoxicillin-clavulanate
Streptococcal pharyngitis	S. pyogenes	Exudates, no cough, fever, adenopathy	Penicillin V or amoxicillin × 10 days
Otitis externa	P. aeruginosa, S. aureus	Pain on auricle traction	Topical ciprofloxacin + hydrocortisone
CAP (outpatient)	S. pneumoniae, Mycoplasma	Fever, cough, consolidation	Amoxicillin or doxycycline × 5 days
CAP (inpatient)	S. pneumoniae, atypicals	CURB-65 ≥2–3	β-lactam + macrolide or fluoroquinolone
HAP/VAP	Pseudomonas, MRSA, Klebsiella	≥48 h post-admission/intubation	Antipseudomonal β-lactam ± aminoglycoside ± MRSA coverage

— Harrison's Principles of Internal Medicine, 22nd Edition (2025, McGraw Hill Medical)

This is a shared conversation. Sign in to Orris to start your own chat.