Pneumonia in adults

Pneumonia is an acute inflammation of the lungs caused by an infection. Initial diagnosis is usually based on a chest x-ray.

Causes, symptoms, treatment, prevention and prognosis depend on whether the infection is bacterial, viral, fungal or parasitic; community-acquired, hospital-acquired or occurs in a nursing home; develops in an immunocompetent patient or against the background of a weakened immune system.

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Epidemiology

Pneumonia is one of the most common infectious diseases. In Europe, the number of patients diagnosed with this disease is 2 to 15 per 1,000 population per year. In Russia, the incidence of community-acquired pneumonia reaches 10-15 per 1,000 population, and in older age groups (over 60 years) - 25-44 cases per 1,000 people per year. Approximately 2-3 million people in the United States suffer from pneumonia annually, approximately 45,000 of whom die. It is the most common hospital-acquired infection with a fatal outcome and the most common cause of death in developing countries.

Despite significant progress in diagnostics and treatment, mortality from this disease is growing. Community-acquired pneumonia is the most common cause of death among all infectious diseases. In the overall structure of causes of death, this disease ranks fifth after cardiovascular, oncological, cerebrovascular diseases and COPD, with mortality reaching 10-33% in the older age group and 25% among children under 5 years of age. Even higher mortality (up to 50%) is typical for so-called hospital-acquired (hospital or nosocomial) and some "atypical" and aspiration pneumonias, which is explained by the highly virulent flora that causes the listed forms of the disease, as well as rapidly developing resistance to traditional antibacterial drugs.

The presence of severe concomitant diseases and certain risk factors, including primary and secondary immunodeficiency, in a significant proportion of patients has a significant impact on the course and prognosis of pneumonia.

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Causes pneumonias

In adults over 30 years of age, the most common pathogens causing pneumonia are bacteria, with Streptococcus pneumoniae dominating across all age groups, socioeconomic conditions, and geographic areas. However, pneumonia can be caused by any pathogen, from viruses to parasites.

The respiratory tract and lungs are constantly exposed to pathogens from the external environment; the upper respiratory tract and oropharynx are especially colonized by the so-called normal flora, which is safe due to the body's immune defenses. If pathogens overcome numerous protective barriers, an infection develops.

Read also: Pneumonia

Upper airway defenses include salivary IgA, proteolytic enzymes, and lysozyme, as well as growth inhibitors produced by normal flora and fibronectin, which coats the mucosa and inhibits adhesion. Nonspecific lower airway defenses include cough, ciliated epithelial clearance, and airway angulation, which prevent airway infection. Specific lower airway defenses are mediated by pathogen-specific immune mechanisms, including IgA and IgG opsonization, anti-inflammatory effects of surfactant, phagocytosis by alveolar macrophages, and T-cell immune responses. These mechanisms protect most individuals from infection. However, in many conditions (e.g., systemic diseases, malnutrition, hospitalization or stay in a nursing home, antibiotic therapy), the normal flora is altered, its virulence increases (e.g., when exposed to antibiotics), or the defense mechanisms are disrupted (e.g., when smoking cigarettes, nasogastric or endotracheal intubation). Pathogenic organisms that in these cases reach the alveolar spaces by inhalation, contact or hematogenous spread, or aspiration can multiply and cause inflammation of the lung tissue.

Specific pathogens causing inflammation of the lung tissue are not isolated in more than half of patients, even with a comprehensive diagnostic examination. However, since certain trends in the nature of the pathogen and the outcome of the disease are detected under similar conditions and risk factors, pneumonias are classified as community-acquired (acquired outside a medical institution), hospital-acquired (including postoperative and associated with artificial ventilation), acquired in nursing homes, and in individuals with weakened immunity; this allows for the appointment of empirical treatment.

The term "interstitial pneumonia" refers to a variety of conditions of unknown etiology characterized by inflammation and fibrosis of the pulmonary interstitium.

Community-acquired pneumonia occurs in people with limited or no contact with health care facilities. Streptococcus pneumoniae, Haemophilus influenzae, and atypical organisms (ie, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella sp) are commonly identified. Symptoms include fever, cough, dyspnea, tachypnea, and tachycardia. Diagnosis is based on clinical presentation and chest radiography. Treatment is with empirically selected antibiotics. Prognosis is good in relatively young and/or healthy patients, but many pneumonias, particularly those caused by S. pneumoniae and influenza virus, are fatal in the elderly and debilitated.

Many microorganisms cause community-acquired pneumonia, including bacteria, viruses, and fungi. Different pathogens predominate in the etiologic pattern depending on the patient's age and other factors, but the relative importance of each as a cause of community-acquired pneumonia is questionable because most patients do not undergo a full evaluation, and even with evaluation, specific agents are detected in less than 50% of cases.

S. pneumoniae, H. influenzae, C. pneumoniae, and M. pneumoniae are the most common bacterial pathogens. Chlamydia and mycoplasma are clinically indistinguishable from other causes. Common viral pathogens include respiratory syncytial virus (RSV), adenovirus, influenza virus, metapneumovirus, and parainfluenza virus in children and influenza in the elderly. Bacterial superinfection may complicate the differentiation of viral from bacterial infections.

C. pneumoniae accounts for 5-10% of community-acquired pneumonias and is the second most common cause of lung infections in healthy individuals aged 5-35 years. C. pneumoniae is commonly responsible for outbreaks of respiratory tract infections in families, educational institutions, and military training camps. It causes a relatively benign form that rarely requires hospitalization. Chlamydia psittaci pneumonia (ornithosis) occurs in patients who own birds.

Overgrowth of other organisms causes infection in the lungs of immunocompetent patients, although the term community-acquired pneumonia is usually applied to the more common bacterial and viral etiologies.

Q fever, tularemia, anthrax, and plague are rare bacterial infections that can cause severe pneumonia; the last three infectious diseases should raise suspicion for bioterrorism.

Adenovirus, Epstein-Barr virus, and Coxsackievirus are common viruses that rarely cause pneumonia. Varicella-zoster virus and gantavirus cause lung infection in adult chickenpox and gantavirus pulmonary syndrome; the new coronavirus causes severe acute respiratory syndrome.

The most common fungal pathogens are Histoplasma (histoplasmosis) and Coccidioides immitis (coccidioidomycosis). Less common are Blastomyces dermatitidis (blastomycosis) and Paracoccidioides braziliensis (paracoccidioidomycosis).

Parasites causing lung disease in patients in developed countries include Plasmodium sp. (malaria), Toxocara canis or catis (migration of larvae into internal organs), Dirofilaria immitis (dirofilariasis), and Paragonimus westermani (paragonimiasis).

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Symptoms pneumonias

Symptoms of pneumonia include malaise, cough, shortness of breath, and chest pain.

The cough is usually productive in older children and adults and dry in infants, young children, and the elderly. Dyspnea is usually mild and occurs with exertion and is rarely present at rest. Chest pain is pleural and localized near the affected area. Inflammation of the lung tissue may manifest as upper abdominal pain when lower lobe infection irritates the diaphragm. Symptoms vary at the extremes of age; infection in infants may manifest as vague irritability and restlessness; in the elderly, as disorientation and confusion.

Manifestations include fever, tachypnea, tachycardia, crackles, bronchial breath sounds, egophony, and dullness to percussion. Signs of pleural effusion may also be present. Nasal flaring, accessory muscle use, and cyanosis are common in infants.

The signs of pneumonia were previously thought to vary depending on the type of pathogen, but there are many common manifestations. In addition, no symptom or sign is sensitive or specific enough to determine the etiology. Symptoms may even resemble non-infectious lung diseases such as pulmonary embolism, neoplasms, and other inflammatory processes in the lungs.

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Diagnostics pneumonias

The diagnosis is suspected based on symptoms and confirmed by chest X-ray. The most severe condition misdiagnosed as pneumonia is pulmonary embolism, which is more likely in patients with minimal sputum production, no concomitant acute respiratory viral infection or systemic symptoms, and no risk factors for thromboembolism.

Chest radiography almost always shows some degree of infiltrate; rarely is there no infiltrate during the first 24 to 48 hours of illness. In general, no specific findings differentiate one type of infection from another, although multilobar infiltrates suggest S. pneumoniae or Legionella pneumophila infection, and interstitial pneumonia suggests a viral or mycoplasmal etiology.

Hospitalized patients should have a complete blood count and electrolytes, blood urea nitrogen, and creatinine to determine hydration status and risk. Two blood cultures are done to detect pneumococcal bacteremia and sepsis, since approximately 12% of all patients hospitalized with pneumonia have bacteremia; S. pneumoniae accounts for two-thirds of these cases.

Research is ongoing to determine whether blood culture results are important enough to guide treatment to justify the cost of testing. Pulse oximetry or arterial blood gas testing should also be performed.

There is usually no indication for testing, including sputum examination, to identify the pathogen; exceptions may be made for critically ill patients in whom a drug-resistant or unusual organism (eg, tuberculosis) is suspected, and patients whose condition deteriorates or who do not respond to treatment within 72 hours. The usefulness of sputum Gram stain and culture remains questionable because specimens are often contaminated and their overall diagnostic yield is low. In patients who do not produce sputum, specimens can be obtained noninvasively by simple expectoration or after inhalation of hypertonic saline, or the patient can undergo bronchoscopy or endotracheal suctioning, which can be easily accomplished through an endotracheal tube in mechanically ventilated patients. In patients with deteriorating conditions and who do not respond to broad-spectrum antibiotic therapy, investigation should include mycobacterial and fungal stains and cultures.

Additional testing is indicated in certain circumstances. People at risk for Legionella pneumonia (eg, patients who smoke, have chronic lung disease, are over 40 years of age, are receiving chemotherapy, or are taking immunosuppressants for organ transplantation) should have a urine test for Legionella antigens, which remains positive long after treatment has begun but only detects L pneumophila serogroup 1 (70% of cases).

A fourfold rise in antibody titers to > 1:128 (or in a single convalescent serum > 1:256) is also considered diagnostic. These tests are specific (95–100%) but not very sensitive (40–60%); thus, a positive test indicates infection, but a negative test does not exclude it.

Infants and young children with possible RSV infection should undergo rapid antigen testing of nasal or throat swabs. No other tests for viral pneumonias exist; viral culture and serologic testing are rarely available in the clinic.

The PCR test (for mycoplasma and chlamydia) is not yet widely available, but has good prospects due to its high sensitivity and specificity, as well as its speed of execution.

A test for SARS-associated coronavirus exists, but its role in clinical practice is unknown and its use is limited outside of known outbreaks. In rare situations, anthrax should be considered.

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Treatment pneumonias

Risk assessment is performed to identify those patients who can be safely treated as outpatients and those who require hospitalization because of a high risk of complications. Risk assessment should support, not replace, clinical data because many unmeasured factors influence the choice of treatment location, including compliance, ability to self-care, and desire to avoid hospitalization. ICU admission is required for patients who require mechanical ventilation and for patients with hypotension (systolic BP < 90 mmHg). Other criteria for ICU admission include a respiratory rate greater than 30/min, PaO2/inspired O2 (PO2) less than 250, multilobar pneumonia, diastolic BP less than 60 mmHg, confusion, and blood urea greater than 19.6 mg/dL. Appropriate treatment includes initiation of antibiotic therapy as soon as possible, preferably within 8 hours of onset. Supportive care for pneumonia includes fluids, antipyretics, analgesics, and O2 for patients with hypoxemia.

Because microorganisms are difficult to identify, antibiotics are selected based on the likely pathogens and the severity of the disease. Consensus guidelines have been developed by many professional organizations. Guidelines should be tailored to local pathogen susceptibility patterns, available medications, and individual patient characteristics. Importantly, none of the guidelines recommend treatment for viral pneumonia.

Ribavirin and specific immune globulin have been used alone or in combination for RSV-associated bronchiolitis in children, but efficacy data are conflicting. Ribavirin is not used in adults with RSV infection. Amantadine or rimantadine 200 mg orally once daily, given within 48 hours of onset of illness, reduces the duration and severity of symptoms in patients with presumed influenza during an epidemic, but efficacy in preventing adverse outcomes of influenza pneumonia is unknown. Zanamivir (10 mg inhaled twice daily) and oseltamivir (75 mg orally twice daily, or 150 mg twice daily in severe cases) are equally effective in reducing the duration of symptoms caused by influenza A or B if started within 48 hours of symptom onset, although zanamivir may be contraindicated in patients with asthma. Acyclovir 5-10 mg/kg IV every 8 hours for adults or 250-500 mg/m2 body surface area IV every 8 hours for children is protective against varicella-zoster virus lung infection. If antiviral treatment is not started within 48 hours of illness onset, antiviral drugs should be given to patients with influenza after 48 hours. Some patients with viral pneumonia, especially influenza, develop additional bacterial infections and require antibiotics against S. pneumoniae, H. influenzae, and Staphylococcus aureus. With empirical therapy, 90% of patients with bacterial pneumonia improve, with improvement in cough and dyspnea, fever, chest pain, and white blood cell count. Failure to improve should raise suspicion for an atypical organism, resistance to an inappropriately broad-spectrum antibiotic, coinfection or superinfection with a second pathogen, obstructive endobronchial disease, immunosuppression, distant foci of infection with reinfection (in the case of pneumococcal infection), or poor adherence to treatment (in the case of outpatients). If none of these causes is confirmed, treatment failure is likely due to inadequate immune defense.

Treatment of viral pneumonia is not carried out, since most viral pneumonias resolve without it.

Patients over 35 years of age should undergo a repeat X-ray examination 6 weeks after treatment; persistence of the infiltrate raises suspicion of a possible malignant endobronchial formation or tuberculosis.

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Prevention

Some forms of community-acquired pneumonia can be prevented by pneumococcal conjugate vaccine (for patients < 2 years), H. influenzae B (HIB) vaccine (for patients < 2 years), and influenza vaccine (for patients > 65 years). Pneumococcal, HIB, and influenza vaccines are also recommended for high-risk patients. High-risk patients not vaccinated against influenza can be given amantadine, rimantadine, or oseltamivir during influenza epidemics.

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Forecast

Outpatient candidates usually improve within 24 to 72 hours. Hospitalized patients may improve or worsen depending on their underlying medical conditions. Aspiration is a major risk factor for death, as are older age, the number and nature of underlying medical conditions, and certain pathogens. Death may be caused by pneumonia itself, progression to a septic syndrome that damages other organs, or exacerbation of underlying medical conditions.

Pneumococcal infection still accounts for approximately 66% of all fatal cases of community-acquired pneumonia with a known pathogen. Overall mortality in hospitalized patients is approximately 12%. Unfavorable prognostic factors include age <1 year or >60 years; involvement of more than one lobe; peripheral blood white blood cell count <5000/μL; comorbidity (heart failure, chronic alcoholism, liver and kidney failure), immunosuppression (agammaglobulinemia, anatomical or functional asplenism), infection with serotypes 3 and 8, and hematogenous dissemination with positive blood cultures or with extrapulmonary complications (arthritis, meningitis, or endocarditis). Infants and children are at particular risk of pneumococcal otitis media, bacteremia, and meningitis.

The mortality rate for Legionella infection is 10-20% among patients with community-acquired pneumonia and is higher among immunosuppressed or hospitalized patients. Patients who respond to treatment recover very slowly, and radiographic changes usually persist for more than 1 month. Most patients require hospitalization, many require respiratory support, and 10-20% die despite adequate antibiotic therapy.

Mycoplasma pneumonia has a favorable prognosis; almost all patients recover. Chlamydia pneumoniae responds more slowly to treatment than mycoplasma and tends to relapse after premature cessation of treatment. Young people usually recover, but mortality among the elderly reaches 5-10%.

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