OVERVIEW

What is community-acquired pneumonia?

Community-acquired pneumonia (CAP), also known as outpatient pneumonia, refers to pneumonia caused by microbial infection in a community setting. This includes pneumonia contracted in the community, cases still in the incubation period, or pneumonia that develops after hospitalization for other reasons, while excluding hospital-acquired pneumonia that manifests after discharge.

The disease primarily presents with chest symptoms such as cough, sputum production, difficulty breathing, and chest pain, as well as systemic symptoms like fever, chills, fatigue, headache, muscle pain, and extrapulmonary symptoms.

Most cases can be effectively treated with antibiotics, supplemented by cough suppressants and expectorants. However, if left untreated, it may lead to severe complications such as respiratory failure, septic shock, or multi-organ failure. Patients do not require isolation during the illness, but their quality of life may be affected.

Is community-acquired pneumonia common?

Yes, it is common.

What are the types of community-acquired pneumonia?

Pathologically, it can be classified into lobar pneumonia, lobular pneumonia, interstitial pneumonia, mixed pneumonia, and miliary pneumonia.

SYMPTOMS

What are the common symptoms of community-acquired pneumonia?

• Chest symptoms:

  • Cough is the most common symptom, often accompanied by sputum production. The frequency of these symptoms shows no significant difference across age groups in adults and the elderly.

  • The incidence of chest pain decreases with age, while rapid breathing becomes more common with age. Hemoptysis is not uncommon.

• Systemic and extrapulmonary symptoms:

  • The vast majority of patients experience fever and chills. Fatigue is very common. Other frequent symptoms include sweating, headache, muscle aches, and loss of appetite.

  • Less common symptoms include sore throat, inability to eat, nausea, vomiting, and diarrhea.

  • In elderly patients, clinical manifestations of pneumonia are often atypical, with fewer respiratory symptoms but more signs such as lethargy, altered mental status, decreased mobility, and cardiovascular changes.

How does community-acquired pneumonia progress?

Most cases of community-acquired pneumonia have an acute onset, but the progression may vary depending on the pathogen, the host's immune status, complications, and age.

What other diseases can community-acquired pneumonia cause?

Parapneumonic effusion (pleural effusion caused by infections such as pneumonia, lung abscess, and bronchiectasis), respiratory failure, septic shock, and multiple organ failure.

CAUSES

What are the common causes of community-acquired pneumonia?

• Bacteria, fungi, chlamydia, mycoplasma, viruses, and parasites can all cause community-acquired pneumonia, with bacteria being the most common, and Streptococcus pneumoniae ranking first.

• Atypical pathogens such as chlamydia and mycoplasma are not uncommon in China, and some cases involve mixed infections. Viral pneumonia has received increasing attention in recent years.

• The distribution or proportion of pathogens varies depending on geographic location, study population, and detection methods. The main pathogen distribution also differs based on disease severity and treatment setting:

  • For outpatients, the order is Streptococcus pneumoniae, Mycoplasma pneumoniae, Haemophilus influenzae, Chlamydia pneumoniae, and respiratory viruses.

  • For hospitalized patients, the order is Streptococcus pneumoniae, Chlamydia pneumoniae, Legionella, and aspiration-related pathogens.

  • For ICU patients, the order is Streptococcus pneumoniae, Staphylococcus aureus, Gram-negative bacilli, and Haemophilus influenzae.

Who is commonly affected by community-acquired pneumonia?

• Weak children and adults, elderly individuals over 60 years old.

• Children and adults with recurrent upper respiratory infections, or those with chronic underlying conditions of the lungs, heart, liver, or kidneys.

• Diabetics, cancer patients, individuals with sickle cell anemia, or Hodgkin's disease.

• Individuals with immune system disorders, those who have undergone splenectomy, or those requiring immunosuppressive therapy.

• Long-term residents of nursing homes or other long-term care facilities.

Is community-acquired pneumonia contagious?

It is somewhat contagious and can spread through respiratory droplets.

Is community-acquired pneumonia hereditary?

No.

DIAGNOSIS

How is community-acquired pneumonia diagnosed?

When diagnosing community-acquired pneumonia, doctors primarily rely on clinical manifestations, hematological and imaging findings, and refer to etiological results.

Clinical diagnostic criteria:

• Community onset;

• Clinical manifestations related to pneumonia:

  • Newly developed cough, sputum production, or worsening of pre-existing respiratory symptoms, with or without purulent sputum, chest pain, dyspnea, or hemoptysis;

  • Fever;

  • Signs of pulmonary consolidation and/or auscultation of moist rales;

  • Peripheral white blood cell count > 10×10⁹/L or < 4×10⁹/L, with or without a left shift.

• Chest imaging: Shows newly developed patchy infiltrates, lobar or segmental consolidation, ground-glass opacities, or interstitial changes, with or without pleural effusion.

A clinical diagnosis can be established if any one of the above three criteria is met, after excluding conditions such as tuberculosis, lung tumors, non-infectious interstitial lung disease, pulmonary edema, atelectasis, pulmonary embolism, eosinophilic lung infiltration, and pulmonary vasculitis.

Etiological diagnosis: Pathogen testing is not routinely required for outpatients. However, it is necessary for patients suspected of infections not typically covered by empirical antibiotic therapy (e.g., tuberculosis) or those unresponsive to initial empirical treatment. Hospitalized patients should undergo relevant pathogen testing.

What tests are needed to diagnose community-acquired pneumonia?

• Hematological tests: Including complete blood count, liver and kidney function tests, blood biochemistry, C-reactive protein, procalcitonin, and blood oxygen levels. These primarily assess the patient's general condition, degree of inflammatory response, and provide references for diagnosis, treatment, and prognosis.

• Imaging tests:

  • Chest X-ray is the basic examination for diagnosis and essential for assessing disease severity;

  • Chest CT scans are more sensitive and detailed than X-rays, playing a crucial role in diagnosis, differential diagnosis, detecting complications, and evaluating disease progression;

  • Ultrasound can be used to detect parapneumonic pleural effusions and lesions near the pleura and guide percutaneous lung biopsies.

TREATMENT

Which department should I visit for community-acquired pneumonia?

Respiratory Medicine, General Practice.

How is community-acquired pneumonia treated?

• Anti-infective therapy: Based on different conditions and treatment settings, considering host factors affecting pathogens, regional and hospital antimicrobial susceptibility data, empirical treatment is recommended after collecting specimens for pathogen testing. Commonly used drugs include penicillins, cephalosporins, and respiratory quinolones.

• Management of complications:

  • Parapneumonic pleural effusion: Early detection, diagnostic thoracentesis, pleural fluid analysis, and chest tube drainage if necessary. Adjust anti-infective regimen based on test results.

  • Respiratory failure, septic shock, multiple organ failure: Provide mechanical ventilation and other related treatments.

Does community-acquired pneumonia require hospitalization?

Assessment is needed. Severity evaluation is crucial for selecting appropriate treatment settings, empirical anti-infective drugs, and supportive care. The commonly used assessment method is the CURB-65 score, which includes 5 criteria (1 point each):

• Confusion;

• Blood urea nitrogen > 7 mmol/L;

• Respiratory rate ≥ 30 breaths/min;

• Systolic blood pressure < 90 mmHg or diastolic blood pressure ≤ 60 mmHg;

• Age ≥ 65 years.

Scores: 0–1 (low risk), 2 (moderate risk), 3–5 (high risk). CURB-65 determines hospitalization needs:

• 0–1: Outpatient treatment in principle;

• 2: Hospitalization or closely monitored outpatient treatment;

• 3–5: Hospitalization required.

However, any scoring system should be combined with factors like age, underlying diseases, socioeconomic status, gastrointestinal function, and treatment compliance.

Can community-acquired pneumonia be completely cured?

Yes.

DIET & LIFESTYLE

What should patients with community-acquired pneumonia pay attention to in their diet?

Provide a high-calorie, high-protein, and high-vitamin diet to ensure adequate nutrient intake, which helps improve immunity and promote recovery.

What should patients with community-acquired pneumonia pay attention to in daily life?

Quit smoking, avoid excessive alcohol consumption, maintain a regular routine, prevent overexertion and insufficient sleep, and engage in physical exercise to strengthen overall health.

Does community-acquired pneumonia require follow-up? How is it done?

Yes.

Monitor changes in symptoms and signs, and conduct hematological and imaging tests.

PREVENTION

Can community-acquired pneumonia be prevented? How to prevent community-acquired pneumonia?

Quit smoking, avoid excessive alcohol consumption, and susceptible individuals can receive multivalent pneumococcal vaccines and influenza vaccines.