Wide spectrum — asymptomatic infection to severe ARDS.

Upper respiratory symptoms predominate in mild disease.

Lower respiratory involvement determines severity and outcome.

Systemic inflammatory phase causes multi-organ manifestations.

Early / mild illness:

• Fever

• Dry cough

• Sore throat

• Rhinorrhea

• Myalgia

• Fatigue

• Headache

Characteristic features:

• Loss of smell (anosmia)

• Loss of taste (ageusia)

• Low-grade fever with malaise

Respiratory involvement:

• Dyspnea

• Chest tightness

• Persistent cough

• Silent hypoxia

Gastrointestinal:

• Diarrhea

• Nausea

• Vomiting

• Abdominal discomfort

Systemic inflammatory phase:

• Cytokine-mediated illness

• Persistent high fever

• Worsening breathlessness

• Profound fatigue

Severe disease:

• Pneumonia

• ARDS

• Sepsis-like picture

• Multi-organ dysfunction

High-risk groups show:

• Rapid deterioration

• Hypoxia

• ICU requirement

Acute hypoxemic respiratory failure (COVID pneumonia → ARDS)

• Diffuse alveolar damage + inflammatory exudate → severe V/Q mismatch, refractory hypoxemia.

• Can progress rapidly around day 5–10 of illness.

Thromboembolism (hypercoagulable state)

• Pulmonary embolism, DVT, arterial thrombosis (stroke/MI) may occur.

• Endothelial injury + inflammation + platelet activation → thrombosis.

Cardiac complications

• Myocarditis / myopericarditis (chest pain, troponin rise, arrhythmia).

• Arrhythmias (AF, VT) and demand ischemia.

• Heart failure exacerbation in vulnerable patients.

Neurologic complications

• Stroke (ischemic > hemorrhagic), encephalopathy, seizures.

• Guillain–Barré syndrome (rare) post-infectious neuropathy.

Secondary infections

• Bacterial pneumonia or sepsis, especially with severe disease, ICU, steroids.

• Fungal infections in high-risk settings (immunosuppression/diabetes).

Renal & multisystem complications

• AKI due to sepsis, hypoxia, microthrombi, dehydration.

• Multiorgan dysfunction in critical illness.

Post-acute sequelae (“Long COVID”)

• Persistent fatigue, dyspnea, cough, “brain fog”, dysautonomia, sleep issues.

• Reduced exercise tolerance; symptoms may last weeks–months.

Pregnancy-related complications (when relevant)

• Higher risk of severe disease, preterm birth, maternal morbidity.

Any acute febrile respiratory illness can mimic COVID-19.

Overlap is highest with viral pneumonias and influenza-like illnesses.

Noninfectious causes of hypoxia must also be considered.

Viral infections:

• Influenza A/B

• RSV infection

• Adenovirus

• Parainfluenza

• Human metapneumovirus

• Other coronaviruses (SARS, MERS, seasonal CoV)

Bacterial respiratory infections:

• Community-acquired pneumonia (Streptococcus pneumoniae)

• Atypical pneumonia (Mycoplasma, Chlamydia)

• Legionella

Other infectious conditions:

• Tuberculosis

• Dengue with respiratory involvement

• Sepsis with ARDS

Non-infectious:

• Pulmonary embolism

• Acute heart failure / pulmonary edema

• Interstitial lung disease flare

• Acute exacerbation of COPD/asthma

• Hypersensitivity pneumonitis

Severe respiratory syndromes:

• ARDS (any cause)

• Cytokine storm syndromes

SARS-CoV-2 infection is the direct cause of COVID-19.

Virus belongs to β-coronavirus family (same lineage as SARS-CoV, MERS-CoV).

Transmission occurs via respiratory droplets, aerosols, and close contact.

Entry occurs through ACE2 receptors in respiratory epithelium.

High viral load in upper airway facilitates rapid community spread.

Variants arise due to RNA mutations and antigenic evolution.

Zoonotic origin suspected (bat reservoir → intermediate host → humans).

Nosocomial transmission significant in early pandemic waves.

Risk of infection increases with crowding, poor ventilation, and close exposure.

Immunity may be incomplete — reinfections possible.

Environmental and host factors influence spread:

• population density

• travel and mobility

• immune status of community

• vaccination coverage

RT-PCR is the gold standard for diagnosis.

Rapid antigen tests detect acute infection with lower sensitivity.

Inflammatory markers help assess severity.

Imaging detects viral pneumonitis and complications.

Coagulation markers indicate thrombotic risk.

Diagnostic tests:

• RT-PCR (nasopharyngeal swab)

• Rapid antigen test

• NAAT-based molecular tests

Hematology:

• Lymphopenia (common finding)

• Mild leukopenia

• Thrombocytopenia (occasionally)

Inflammatory markers:

• CRP elevation

• Ferritin

• IL-6 (severe cases)

• Procalcitonin (to rule out bacterial superinfection)

Coagulation profile:

• Elevated D-dimer

• Prolonged PT (in severe disease)

Organ function tests:

• Liver enzymes (mild transaminitis)

• Serum creatinine (renal involvement)

• Cardiac enzymes (troponin if myocarditis suspected)

Imaging:

• Chest X-ray — bilateral patchy infiltrates

• HRCT chest — ground-glass opacities

• CT severity scoring in moderate–severe disease

Additional:

• Arterial blood gas (hypoxia assessment)

• Echocardiography (if cardiac involvement suspected)

Clinical turning point often occurs around day 5–10

• Worsening dyspnea/hypoxia after initial fever phase suggests inflammatory lung involvement.

Hypoxia may be “silent”

• Patients may look comfortable but SpO₂ low → pulse oximetry is important.

Steroids timing matters

• Helpful in hypoxic disease, harmful/unhelpful in mild non-hypoxic disease.

Think thrombosis when hypoxia is disproportionate

• Sudden hypoxia, pleuritic chest pain, tachycardia → evaluate for PE/DVT.

Long COVID is real and needs follow-up

• Persistent fatigue/dyspnea/cognitive symptoms can impair function; reassure and plan review.

Virus enters via respiratory tract and binds ACE2 receptors on epithelial cells.

Spike (S) protein facilitates viral entry through TMPRSS2-mediated membrane fusion.

Initial replication occurs in nasopharyngeal and bronchial epithelium.

Viral replication leads to cell injury and local inflammatory response.

Innate immune activation triggers interferons and pro-inflammatory cytokines.

In severe cases, dysregulated immune response causes cytokine storm.

Diffuse alveolar damage leads to impaired gas exchange and hypoxia.

Endothelial injury promotes microvascular thrombosis and hypercoagulability.

Systemic inflammation may affect heart, kidneys, brain, and GI tract.

ACE2 downregulation contributes to RAAS imbalance and lung injury.

Early phase:

• Viral replication dominant

• Mild constitutional and respiratory symptoms

Pulmonary phase:

• Inflammatory lung injury

• Hypoxia and radiologic infiltrates

Hyperinflammatory phase (severe cases):

• Elevated IL-6, CRP, ferritin, D-dimer

• ARDS and multiorgan dysfunction

Long-COVID mechanism (post-acute phase):

• Persistent immune dysregulation

• Possible viral persistence or autoimmunity

• Microvascular dysfunction

Diffuse alveolar damage (DAD) is the core lung pathology in severe COVID

• Hyaline membranes, edema, inflammatory infiltrates → ARDS picture.

Microvascular injury and thrombosis are characteristic

• Endothelialitis + microthrombi → worsened hypoxia and organ injury.

Inflammatory phase can drive tissue damage

• Cytokine pathways contribute to systemic inflammation and multiorgan effects.

Secondary bacterial infection may add consolidation

• If lobar consolidation appears, consider bacterial superinfection.

Vaccination reduces severe disease, ICU admission, and death

• Boosters improve protection over time, especially in high-risk groups.

Masking reduces droplet + aerosol transmission in crowded indoor settings

• Better protection with good fit and quality mask.

Ventilation is a strong prevention tool

• Outdoor/ventilated spaces lower risk; avoid poorly ventilated crowding.

Hand hygiene and cough etiquette reduce spread

• Especially for shared surfaces and close contact.

Isolation when symptomatic reduces household/community transmission

• Early separation and masking at home protects family members.

Protect high-risk individuals

• Elderly, diabetes, CKD, lung disease: prioritize vaccination and early testing/early treatment.

Chest X-ray may be normal early in mild disease

• Abnormalities increase with moderate/severe disease.

Typical CXR pattern: bilateral, peripheral, lower-zone opacities

• Patchy air-space opacities; may progress to diffuse involvement (ARDS).

CT chest (when used) often shows ground-glass opacities

• Peripheral/subpleural GGOs ± “crazy paving”; consolidation in later phase.

Imaging helps assess severity and complications

• Sudden deterioration → consider PE, pneumothorax, superadded bacterial pneumonia.

COVID-19 is caused by SARS-CoV-2 variants, not classical “serotypes”

• Variants arise from mutations in spike and other genes.

Variants differ mainly in transmissibility and immune escape

• Some variants spread faster; reinfections can occur.

Clinical severity varies by host factors more than variant alone

• Age, comorbidities, immune status strongly influence severity.

(Optional teaching line)

• If you want: list historically important VOCs as examples, but avoid long lists unless needed.

(You’re right — for COVID-19 we should label it as Variants / lineages (not “serotypes”). Paste this into your Serotypes / Subtypes section.

COVID-19 — Variants / Subtypes (Jeevanam TXT)

COVID-19 is caused by SARS-CoV-2 variants (lineages), not classical serotypes

• Variants are defined by genome mutations (especially spike) and are grouped into lineages/clades.

WHO naming for important variants

• Variants are categorized as Variants of Concern (VOC) / Variants of Interest (VOI) depending on impact.

Major historical variant families (examples for teaching)

• Alpha (B.1.1.7)

• Beta (B.1.351)

• Gamma (P.1)

• Delta (B.1.617.2)

• Omicron (B.1.1.529) → many sublineages

Omicron sublineages (examples)

• BA.1, BA.2, BA.4/BA.5

• Later sublineages may show increased immune escape (reinfections possible).

What variants change clinically

• Transmissibility and immune escape can differ by variant.

• Severity is influenced strongly by age, comorbidities, and prior immunity (vaccination/infection), not only variant type.

Practical note

• Clinically, we usually treat by severity and risk category, not by variant name, unless public health typing is available.

Fever is the most consistent clinical sign.

Tachypnea indicates lower respiratory tract involvement.

Hypoxia may occur even with mild symptoms (“silent hypoxia”).

Crepitations suggest viral pneumonitis involvement.

General examination:

• Fever

• Tachycardia

• Tachypnea

• Fatigue appearance

Respiratory signs:

• Low SpO₂ (<94%)

• Increased work of breathing

• Accessory muscle use

• Bilateral basal crepitations

• Reduced air entry (in pneumonitis)

Severe disease indicators:

• Silent hypoxia

• Cyanosis (late sign)

• Altered mental status

• Hypotension

Systemic involvement signs:

• Dehydration

• Delirium (elderly)

• Signs of thromboembolism (leg swelling, chest pain)

COVID-19 is a respiratory viral illness caused by SARS-CoV-2.

Transmission occurs primarily via respiratory droplets and aerosols.

Clinical spectrum ranges from asymptomatic infection to severe viral pneumonia and multiorgan failure.

Severe disease is driven by dysregulated immune response and hyperinflammation (“cytokine storm”).

SARS-CoV-2 primarily targets ACE2 receptors in respiratory epithelium.

Complications include ARDS, thrombosis, myocarditis, and long-COVID syndromes.

Older age, obesity, diabetes, cardiovascular disease, and immunosuppression increase severity risk.

Most infections are mild or moderate, presenting with fever, cough, fatigue, and anosmia.

A subset progresses to hypoxia and inflammatory lung injury requiring hospitalization.

Post-acute sequelae (long-COVID) may persist for months.

Fever and constitutional symptoms are most common initial presentation.

Dry cough is the hallmark respiratory symptom.

Fatigue and myalgia reflect systemic inflammatory response.

Loss of smell (anosmia) and taste (ageusia) are early and characteristic.

Shortness of breath indicates lower respiratory tract involvement.

Common early symptoms:

• Fever

• Dry cough

• Fatigue

• Myalgia

• Headache

• Sore throat

• Nasal congestion

Neurological / sensory:

• Anosmia

• Ageusia

• Dizziness

• Confusion (in elderly)

Respiratory progression:

• Dyspnea

• Chest tightness

• Increased respiratory effort

Gastrointestinal:

• Diarrhea

• Nausea

• Vomiting

• Abdominal discomfort

Severe disease symptoms:

• Persistent breathlessness

• High fever not settling

• Hypoxia-related fatigue

• Reduced oral intake

Post-acute / Long-COVID symptoms:

• Persistent fatigue

• Brain fog

• Palpitations

• Exercise intolerance

• Sleep disturbance

Any acute febrile respiratory illness can mimic COVID-19.

Overlap is highest with viral pneumonias and influenza-like illnesses.

Noninfectious causes of hypoxia must also be considered.

Viral infections:

• Influenza A/B

• RSV infection

• Adenovirus

• Parainfluenza

• Human metapneumovirus

• Other coronaviruses (SARS, MERS, seasonal CoV)

Bacterial respiratory infections:

• Community-acquired pneumonia (Streptococcus pneumoniae)

• Atypical pneumonia (Mycoplasma, Chlamydia)

• Legionella

Other infectious conditions:

• Tuberculosis

• Dengue with respiratory involvement

• Sepsis with ARDS

Non-infectious:

• Pulmonary embolism

• Acute heart failure / pulmonary edema

• Interstitial lung disease flare

• Acute exacerbation of COPD/asthma

• Hypersensitivity pneumonitis

Severe respiratory syndromes:

• ARDS (any cause)

• Cytokine storm syndromes