Pneumonia — Types, Causes, CURB-65, Antibiotics & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Pneumonia is an acute infection of the lung parenchyma — the alveoli and surrounding tissue — causing inflammation and fluid accumulation that impairs gas exchange. It is the world's leading infectious cause of death, killing approximately 2.5 million people annually including 808,000 children under 5. Pneumonia is classified by acquisition setting: Community-acquired pneumonia (CAP) — the most common type, acquired outside hospital or within 48 hours of admission; Hospital-acquired (nosocomial) pneumonia (HAP) — onset more than 48 hours after hospital admission; Ventilator-associated pneumonia (VAP) — in mechanically ventilated patients; and Aspiration pneumonia — from inhalation of oropharyngeal secretions. Streptococcus pneumoniae (pneumococcus) is the most common bacterial cause of CAP globally. Despite its severity, the majority of CAP cases in previously healthy adults can be managed as outpatients with oral antibiotics guided by severity assessment.

Bacterial causes of CAP: Streptococcus pneumoniae (pneumococcal pneumonia — most common, causes lobar consolidation, often with pleurisy); Haemophilus influenzae (particularly in COPD patients and the elderly); Staphylococcus aureus (post-influenza, severe — MRSA in community-acquired cases increasingly); Mycoplasma pneumoniae (atypical pneumonia — walking pneumonia — in younger adults, often clusters in schools/universities); Chlamydophila pneumoniae (atypical — typically mild); Legionella pneumophila (Legionnaire's disease — from water systems — particularly air conditioning towers; severe, with relative bradycardia, hyponatraemia, and deranged liver function). Viral causes: influenza A and B (seasonal; may cause primary viral or secondary bacterial pneumonia); COVID-19 (SARS-CoV-2); RSV (Respiratory Syncytial Virus — major cause in children and increasingly recognised in older adults and the immunocompromised); parainfluenza; adenovirus. Fungal causes (predominantly immunocompromised patients): Pneumocystis jirovecii (PCP — in HIV, solid organ transplant, haematological malignancy); Aspergillus fumigatus (invasive aspergillosis). Risk factors: age extremes (under 5, over 65); cigarette smoking (damages mucociliary clearance); chronic disease (COPD, heart failure, diabetes, CKD, liver disease); immunosuppression; aspiration risk (stroke, dysphagia, alcoholism, seizures); and malnutrition.

Classic bacterial pneumonia symptoms: acute onset of fever (typically above 38 degrees C), rigors (uncontrollable shivering), productive cough (purulent yellow-green sputum — or rusty brown sputum characteristic of pneumococcal pneumonia), pleuritic chest pain (sharp, stabbing, worse on inspiration — from pleural inflammation), and breathlessness (dyspnoea). Atypical pneumonia (Mycoplasma, Chlamydophila): gradual onset over 1-2 weeks, dry persistent cough, headache, malaise, and extrapulmonary features (rash, ear pain, erythema multiforme for Mycoplasma). Physical signs on examination: fever, tachycardia, tachypnoea (respiratory rate above 20/min — the most sensitive clinical predictor of severity); reduced oxygen saturations (SpO2 below 94%); dull percussion note over consolidation; bronchial breathing (harsh tubular breath sounds over consolidated lobe); and crackles. Severity indicators forming CURB-65 score: Confusion (new onset), Urea above 7 mmol/L, Respiratory rate above 30/min, Blood pressure below 90/60 mmHg, and age above 65 — each scores 1 point; score 0-1: low mortality, outpatient; 2: moderate, consider admission; 3-5: high mortality, hospital admission.

Chest X-ray (CXR): the essential diagnostic investigation — consolidation (homogeneous opacity in a lobar or segmental distribution), air bronchograms (air-filled bronchi visible within consolidated lung), or bilateral interstitial infiltrates (viral/atypical pattern). Blood tests: FBC (elevated white cell count — neutrophilia in bacterial, lymphopenia in viral); CRP (typically above 100 mg/L in bacterial CAP — markedly elevated); PCT (procalcitonin — above 0.25 ng/mL supports bacterial infection; guides antibiotic stewardship); U+E (urea above 7 mmol/L = CURB-65 point); and blood cultures (before antibiotics in hospitalised patients — positive in 10-15% of CAP). Urinary antigen tests: Streptococcus pneumoniae urinary antigen (sensitive and specific — positive within hours of illness onset; useful in antibiotic pre-treated patients); Legionella urinary antigen (detects serogroup 1 — the most common Legionella subtype). Sputum culture: in moderate-severe CAP — useful if Staphylococcus or resistant organisms are suspected. SARS-CoV-2 and influenza PCR: in respiratory illness during active seasonal periods or outbreak situations. CT chest: more sensitive than CXR — reveals pneumonia not visible on plain film and identifies complications (empyema, cavitation, abscess).

Antibiotic treatment is guided by severity (CURB-65) and likely organism. Low-severity CAP (CURB-65 0-1, managed at home): amoxicillin 500 mg three times daily for 5 days (NICE 2019 — 5-day course sufficient for low-severity CAP); if atypical organism suspected or known penicillin allergy: doxycycline 200 mg day 1 then 100 mg once daily for 5 days, or clarithromycin 500 mg twice daily. Moderate-severity CAP (CURB-65 2): hospital admission; dual therapy — co-amoxiclav (amoxicillin/clavulanate) PLUS clarithromycin or doxycycline (covers both typical and atypical organisms). High-severity CAP (CURB-65 3-5, or requiring HDU/ICU): IV co-amoxiclav 1.2 g TID plus IV clarithromycin 500 mg BD; or IV piperacillin/tazobactam plus clarithromycin for more severe or aspiration cases. Legionella: IV clarithromycin or fluoroquinolone (levofloxacin) — dual therapy in severe disease. PCP pneumonia (in HIV, CD4 below 200): high-dose co-trimoxazole (trimethoprim/sulfamethoxazole) IV/oral plus prednisolone for moderate-severe PCP. Viral pneumonia: oseltamivir (Tamiflu) for influenza; nirmatrelvir/ritonavir (Paxlovid) for COVID-19 pneumonia in high-risk groups within 5 days of symptoms. Supportive care: supplemental oxygen (target SpO2 94-98%, or 88-92% in COPD); IV fluids if dehydrated; antipyretics; physiotherapy; and appropriate positioning.

Pneumonia causes significant complications, particularly in vulnerable patients and those with delayed or inadequate treatment. Parapneumonic effusion and empyema: inflammation of the pleura causes fluid accumulation (parapneumonic effusion — in up to 40% of hospitalised CAP patients); if infected, it becomes empyema — pus in the pleural space — requiring chest drain insertion and sometimes surgical decortication. Lung abscess: necrotic liquefaction within the consolidated area creates a cavity — caused by anaerobes (aspiration) or Staphylococcus aureus; treated with prolonged antibiotics (4-6 weeks). Sepsis and septic shock: bacteraemia occurs in 10-15% of hospitalised CAP — septicaemia from pneumococcal pneumonia carries a 30% mortality risk; septic shock requires ITU admission, IV fluids, vasopressors, and broad-spectrum antibiotics. Respiratory failure: hypoxaemic respiratory failure (type 1) requiring supplemental oxygen or high-flow nasal cannula; acute respiratory distress syndrome (ARDS) from bilateral pneumonia or sepsis — mortality 35-40%. Acute kidney injury (AKI): from sepsis-related hypoperfusion. Post-pneumonia fatigue and reduced lung function: persistent symptoms for 4-8 weeks after apparent recovery; a follow-up chest X-ray at 6 weeks is recommended to exclude underlying malignancy masking as pneumonia.

Vaccination is the most effective pneumonia prevention strategy. Pneumococcal vaccine: PCV13 (Prevenar 13 — conjugate, 13 serotypes) and PPV23 (polysaccharide, 23 serotypes) are recommended for all adults over 65 and for high-risk groups (asplenia, chronic lung/heart/kidney/liver disease, diabetes, immunosuppression). Newer PCV15 and PCV20 conjugate vaccines provide broader coverage. Influenza vaccine: annual flu vaccination reduces influenza-associated pneumonia risk — recommended for all over 65, pregnant women, healthcare workers, and high-risk individuals. COVID-19 vaccination (primary series plus boosters): dramatically reduces risk of severe SARS-CoV-2 pneumonia and hospitalisation. Smoking cessation: smoking is the most important modifiable risk factor for CAP in adults — restoring mucociliary function and reducing susceptibility. Dysphagia management: for stroke patients and patients with neurological conditions — speech and language therapy (SALT) assessment to reduce aspiration risk. Good hand hygiene and respiratory etiquette. Children under 5 in low-income countries benefit enormously from Haemophilus influenzae type b (Hib), measles, and pneumococcal vaccinations.

Call 999 or go to emergency immediately if you or someone else has: breathing rate above 30 breaths per minute; blue lips or fingertips (cyanosis); oxygen saturation below 92% on pulse oximetry; confusion or altered mental state; blood pressure below 90/60 mmHg; or inability to maintain oral intake. See a GP urgently (same day or next day) for: fever with cough and breathlessness; chest pain that is worse on breathing; cough producing blood-stained or rusty sputum; symptoms not improving after 48 hours of antibiotic treatment; or any fever and breathlessness in an immunocompromised patient, infant, elderly person, or someone with underlying lung or heart disease. A respiratory rate above 20/min with fever should prompt clinical assessment. Pneumonia symptoms can initially resemble a bad chest cold — do not delay seeking medical review if symptoms are worsening rather than improving after 3-5 days.