Definition and classification of pneumonia
Pneumonia is an inflammation of the lungs. Classification is essential for understanding prognosis, typical pathogens, and selecting treatment tactics.
The pathoanatomical classification includes lobar pneumonia, bronchopneumonia, and interstitial pneumonia. They differ in the extent and nature of lung tissue involvement, as well as typical causative agents.
Depending on the type of pathogen, typical and atypical pneumonia are distinguished:
- Typical pneumonia is caused by extracellular pathogens, such as Streptococcus pneumoniae. It is characterized by a vivid clinical presentation, high fever, and clear opacities on X-ray.
- Atypical pneumonia is caused by intracellular pathogens, such as Mycoplasma. The course is milder, and the radiographic picture may be blurred, making differentiation from bronchitis difficult. It requires a different antibiotic therapy.
The primary classification determining the approach is based on the site of infection: community-acquired pneumonia and hospital-acquired pneumonia. Community-acquired pneumonia is not associated with hospitalization and features a typical and predictable flora. Hospital-acquired pneumonia develops 48–72 hours after hospital admission or within 4 weeks after discharge, is associated with antibiotic-resistant microflora, often has a severe course, and may be associated with mechanical ventilation. The designation "community-acquired" or "hospital-acquired" must be included in the diagnosis formulation.
Clinical presentation and physical examination
Classic symptoms of pneumonia include shortness of breath, febrile fever, cough, pleuritic chest pain, and fatigue. In infants, the elderly, and immunocompromised patients, the classic presentation may be absent: in the elderly, impaired consciousness or cognitive decline without prominent fever is often the first manifestation.
Auscultation reveals:
- fine crackles and crepitus;
- decreased breath sounds;
- bronchial breathing in the presence of consolidation;
- enhanced bronchophony.
Percussion and palpation reveal dullness to percussion, enhanced vocal fremitus, and lagging of one half of the chest during breathing.
Initial diagnostics
At the initial presentation (emergency department or outpatient visit), a blood test and diagnostic imaging are sufficient. Radiography is performed first; CT is reserved for unclear cases or comorbidities such as COPD.
X-ray confirms the diagnosis and determines the extent of lung tissue involvement, while blood tests help assess severity and determine further management.
Pneumonia is a clinical diagnosis: decisions are made based on a combination of data, as the classic set of signs (crackles, fever, blood test changes) may not be fully present. The choice between X-ray and CT relies on clinical judgment rather than a rigid algorithm.
Severity assessment and site-of-care selection
The first key question is where to treat the patient. For this purpose, the CURB-65 and PSI scales are used. CURB-65 is simpler and can be calculated without a calculator; PSI takes more factors into account and requires specialized calculation, but more accurately identifies patients who will truly benefit from hospitalization. The modification of CURB-65 without the urea parameter is called CRB-65 and allows treatment decisions to be assessed without laboratory data, with the threshold lowered by 1 point: 0 points mean outpatient treatment, 1 or more indicate the need for inpatient care.
Decision-making algorithm:
- assessment for life-threatening conditions — septic shock or acute respiratory failure requiring mechanical ventilation; if present, immediate admission to the intensive care unit is indicated;
- assessment of the feasibility of home treatment — availability of care, cognitive or mental impairments, ability to swallow pills;
- assessment of oxygen saturation — a persistent value above 92% allows for outpatient treatment;
- application of the CURB-65 or PSI scale for the final decision.
Upon hospitalization, additional criteria for referral to the intensive care unit are assessed: hypotension, temperature below 36°C, respiratory rate over 30 breaths per minute, PaO2/FiO2 ratio less than 250, blood urea nitrogen over 7, leukopenia, thrombocytopenia, and multilobar lung involvement. Three or more criteria indicate treatment in the ICU, while two or fewer indicate a general therapeutic ward.
Antibiotic Therapy
Outpatient treatment depends on the patient's age and comorbidities. Patients under 65 years old without structural lung disease and significant comorbidities do not require amoxicillin with clavulanic acid — amoxicillin monotherapy is preferred, which reduces antibiotic resistance and the risk of diarrhea associated with clavulanic acid. Combination with clavulanic acid is indicated for patients over 65 or those with comorbidities.
If atypical flora is suspected, one of two approaches is used: immediately combining the baseline antibiotic with an agent covering atypical flora, or prescribing baseline therapy and adding an anti-atypical agent if therapy proves ineffective.
Macrolide monotherapy (clarithromycin, azithromycin) in case of beta-lactam allergy is permissible only if pneumococcal resistance to macrolides is below 25%; in Russia, this figure has approached 24–25%, so macrolide monotherapy is not recommended. In the case of combined beta-lactam allergy and QT interval prolongation (due to sotalol or amiodarone use), doxycycline is the drug of choice.
In the inpatient setting, the choice of therapy depends on the presence of risk factors for MRSA and Pseudomonas aeruginosa (known colonization, prior infection, microscopy data, hospitalization with intravenous antibiotics in the past three months):
- without risk factors — an antineutrum beta-lactam with doxycycline or a macrolide, or respiratory fluoroquinolone monotherapy;
- MRSA risk — vancomycin or linezolid is added;
- Pseudomonas aeruginosa risk — antipseudomonal beta-lactam or fluoroquinolone;
- in case of beta-lactam allergy (excluding life-threatening reactions), fluoroquinolones are used; for Pseudomonas aeruginosa risk — levofloxacin with aztreonam and an aminoglycoside.
Treatment efficacy is assessed by temperature reduction within 24–48 hours. The course duration is at least 5 days, up to 7 days if symptoms persist. Cough, fatigue, auscultatory changes, and radiographic findings may persist after clinical recovery and are not criteria for treatment failure, as radiological changes can last up to a month.
Further evaluation and follow-up
Upon hospitalization, tests performed at the initial visit are repeated and supplemented with blood cultures, sputum microscopy and culture, pneumococcal and Legionella antigen testing, and throat sputum PCR. Blood cultures, microscopy, and sputum cultures are the most preferred investigations.
After identifying the pathogen, therapy is narrowed to targeted drugs, and upon a positive response, the patient is switched from intravenous or intramuscular administration to oral intake. Procalcitonin can be used as a marker to decide on discontinuing antibiotic therapy, but not as a criterion for initiating it.
If pneumonia does not resolve, it is necessary to search for resistant flora, consider bronchoscopy, CT, in some cases thoracoscopy, and rule out tuberculosis and lung malignancy. Patients with lung cancer risk factors are recommended a follow-up chest X-ray 4 weeks after recovery.
Key points
- Pneumonia is classified pathoanatomically, by pathogen type (typical/atypical), and by site of infection (community-acquired/hospital-acquired) — the latter determines treatment management.
- In elderly and immunocompromised patients, classic symptoms may be absent, with altered mental status being the first sign.
- Initial diagnostics include blood tests and radiography; CT is reserved for unclear cases.
- CURB-65/CRB-65 and PSI scales are used to determine the site of care — outpatient or inpatient.
- Criteria for ICU admission include hypotension, severe tachypnea, low PaO2/FiO2, leukopenia and thrombocytopenia, and multilobar involvement.
- Amoxicillin with clavulanic acid is not required for patients under 65 without comorbidities.
- Macrolide monotherapy is limited due to increasing pneumococcal resistance in Russia.
- Temperature reduction within 24–48 hours is the primary criterion for treatment efficacy; X-ray and auscultation lag behind the clinical presentation.