Pneumococcal pneumonia is a type of pneumonia caused by Streptococcus pneumoniae (SP), also known as pneumococcus. It accounts for approximately half of all cases of community-acquired pneumonia (CAP). The disease typically has an abrupt onset, characterized by high fever, rigors, cough, blood-tinged sputum, and chest pain. Chest imaging often reveals acute inflammatory consolidation in a lung segment or lobe. Due to the widespread use of antibiotics, the onset, symptoms, and radiographic features of this disease have become less typical.
Etiology and Pathogenesis
SP is a Gram-positive coccus that commonly appears in pairs (diplococci) or short chains. It has a capsule, and its virulence is related to the structure and amount of polysaccharides in the capsule. Based on the antigenic properties of the capsular polysaccharides, SP can be classified into 86 serotypes. In adults, the most common pathogenic serotypes are types 1-9 and 12, with type 3 being the most virulent. In children, types 6, 14, 19, and 23 are more common. SP can survive for months in dried sputum but is easily killed by direct sunlight exposure for 1 hour or heating at 52°C for 10 minutes. It is also highly sensitive to disinfectants like phenol.
In individuals with normal immune function, SP is part of the normal flora residing in the oral cavity and nasopharynx. The carriage rate varies with age, season, and immune status. When immune function is impaired, virulent SP can invade the body and cause disease. In addition to pneumonia, SP can occasionally lead to bacteremia or septic shock, with severe cases more common in older adults and infants.
SP does not produce toxins, nor does it cause tissue necrosis or cavitation. Its pathogenicity lies in the invasive action of the high-molecular polysaccharide capsule on tissues. The infection initially causes pulmonary edema in the alveolar walls, followed by exudation of white and red blood cells. The exudate, containing bacteria, spreads centripetally through the pores of Cohn to involve multiple lung segments or even entire lobes. Since the lesion begins in the peripheral lung, the boundaries between lobes are distinct, and the pleura is often involved, leading to exudative pleuritis.
Pathology
The pathological changes in pneumococcal pneumonia can be divided into four stages: congestion, red hepatization, gray hepatization, and resolution. These stages are characterized by pulmonary congestion and edema, serous exudation into the alveoli, infiltration of red and white blood cells, phagocytosis of bacteria by white blood cells, and subsequent dissolution and resorption of fibrinous exudates, with re-aeration of the alveoli. However, these pathological stages are now rarely observed due to the early use of antibiotics. After resolution, the lung tissue structure is generally preserved without fibrous scarring. In rare cases, incomplete resorption of fibrin within the alveoli may lead to fibroblast formation, resulting in organizing pneumonia. In older individuals and infants, the infection may follow a bronchial distribution (bronchopneumonia). If untreated, 5%-10% of patients may develop empyema, and 10%-20% may experience extrapulmonary infections such as meningitis, pericarditis, endocarditis, arthritis, or otitis media due to bacterial dissemination through lymphatic or thoracic ducts into the bloodstream.
Clinical Manifestations
Pneumococcal pneumonia is more common in winter and early spring and often occurs alongside respiratory viral infections. It predominantly affects previously healthy young adults, as well as older adults and infants, with a higher incidence in males. Individuals who smoke, have dementia, chronic bronchitis, bronchiectasis, congestive heart failure, chronic illnesses, or are immunosuppressed are more susceptible to SP infection.
Symptoms
Patients often have a history of cold exposure, rain-soaking, fatigue, or viral infections prior to onset. The disease begins abruptly with high fever, rigors, and generalized muscle aches. Body temperature rises to 39-40°C within hours, peaking in the afternoon or evening, and may present as persistent fever. Tachycardia often accompanies the fever. Patients may experience unilateral chest pain radiating to the shoulder or abdomen, which worsens with coughing or deep breathing. Sputum is scant but may be blood-tinged or rust-colored. Appetite is significantly reduced, and some patients may experience nausea, emesis, abdominal pain, or diarrhea, which can lead to misdiagnosis as an acute abdominal condition.
Signs
Patients often appear acutely ill, with flushed cheeks, nasal flaring, and hot, dry skin. Herpes simplex may be present around the mouth or nose. In extensive lung involvement, cyanosis may occur. In cases of severe infection, petechiae on the skin or mucosa and scleral icterus may be observed. Early in the disease, lung examination may reveal minimal abnormalities, with reduced chest wall movement, slight dullness on percussion, and diminished breath sounds along with pleural friction rubs. During consolidation, percussion reveals dullness, tactile fremitus is increased, and bronchial breath sounds may be heard. Moist rales may be audible during the resolution phase. Tachycardia and occasionally arrhythmias may occur. Severe cases may present with abdominal distension or tenderness in the upper abdomen, often related to diaphragmatic pleural involvement. In critical infections, complications such as shock, acute respiratory distress syndrome (ARDS), and neuropsychiatric symptoms may develop.
The natural course of the disease is approximately 1-2 weeks. Within 5-10 days after onset, body temperature may spontaneously decline abruptly or gradually. With effective antibiotic therapy, fever typically resolves within 1-3 days, and other symptoms and signs gradually disappear.
Complications
Complications of pneumococcal pneumonia have become rare in recent years. Patients with severe infections and toxemia are prone to developing septic shock, especially older individuals. This is characterized by hypotension, cold extremities, diaphoresis, cyanosis, tachycardia, and arrhythmias. However, symptoms such as high fever, chest pain, and cough are not particularly prominent. Other complications include pleuritis, empyema, pericarditis, meningitis, and arthritis.
Laboratory and Other Examinations
Blood Tests
White blood cell (WBC) count is elevated, with neutrophils typically accounting for more than 80%, accompanied by a left shift in the neutrophil nucleus. In older, debilitated, alcoholic, or immunocompromised patients, the WBC count may not increase, but the percentage of neutrophils remains high.
Sputum Analysis
Direct smear of sputum with Gram staining and capsule staining under microscopy can identify typical Gram-positive diplococci or chains with capsules, providing a preliminary etiological diagnosis. Sputum culture can confirm the pathogen within 24-48 hours. Sputum samples should be collected promptly after mouth rinsing and before antibiotic use, using deep, purulent, or rust-colored sputum. Polymerase chain reaction (PCR) and fluorescent antibody detection can improve diagnostic accuracy. SP antigen in urine may also test positive.
Blood Cultures
Approximately 10%-20% of patients develop bacteremia, so blood cultures should be performed in severe cases.
Pleural Effusion Analysis
If pleural effusion is present, fluid should be aspirated for bacterial culture.
Chest Imaging
Early-stage findings may show only increased pulmonary markings or slight blurring of affected lung segments or lobes. As the disease progresses, large areas of inflammatory infiltration or consolidation appear, with air bronchograms visible within consolidated regions. The costophrenic angle may show small amounts of pleural effusion. During the resolution phase, inflammatory infiltrates gradually resolve. Some areas may resolve faster, presenting a pseudocavitation sign. Most cases resolve completely within 3-4 weeks after onset. In older patients, resolution may be slower, and incomplete resorption can lead to organizing pneumonia.
Diagnosis
A preliminary diagnosis can be established based on typical symptoms and signs in combination with chest X-ray findings. However, in older or debilitated patients, or those with secondary infections or focal pneumonia, clinical presentations may be atypical, requiring careful differentiation. Pathogen identification is the key to a definitive diagnosis.
Treatment
Antibiotic Therapy
The first-line treatment is penicillin G, with the route of administration and dosage determined by the severity of the disease and the presence of complications.
For mild cases, 2.4 million units per day can be administered in three intramuscular injections, or procaine penicillin 600,000 units intramuscularly every 12 hours.
For moderate cases, penicillin G 2.4-4.8 million units per day is recommended, administered via intravenous infusion in divided doses every 6-8 hours.
For severe cases or those with meningitis, the dosage can be increased to 10-30 million units per day, divided into four intravenous infusions.
Given the increasing rate of penicillin resistance in SP and the raised minimum inhibitory concentration (MIC) thresholds, the European guidelines for managing lower respiratory tract infections recommend high-dose penicillin therapy. For suspected SP pneumonia, penicillin G at 3.2 million units every 4 hours is effective against SP with an MIC ≤ 8 mg/L. This approach also helps prevent the spread of resistant SP, methicillin-resistant Staphylococcus aureus (MRSA), and Clostridioides difficile caused by the use of broad-spectrum antibiotics.
For patients who are allergic to penicillin or infected with penicillin-resistant strains, alternative treatments include respiratory fluoroquinolones, cefotaxime, or ceftriaxone. For infections caused by multidrug-resistant (MDR) strains, options such as vancomycin, teicoplanin, or linezolid can be used.
Supportive Therapy
Patients should remain on bed rest while receiving adequate protein, calories, and vitamins. Close monitoring of the patient's condition is necessary to prevent shock. For severe chest pain, small doses of analgesics may be considered. Aspirin or other antipyretic and anti-inflammatory drugs are not recommended, as they may cause excessive sweating, dehydration, and interference with the true fever pattern, potentially leading to diagnostic errors.
Adequate hydration, with a daily intake of 1-2 liters of water, is encouraged. Intravenous fluids may be administered in cases of dehydration. For patients with hypoxemia or severe conditions (PaO2 < 60 mmHg or with cyanosis), oxygen therapy is indicated.
In cases of significant paralytic ileus or gastric distension, fasting, withholding of fluids, and gastrointestinal decompression may be necessary until bowel motility recovers. For agitation, delirium, or insomnia, sedatives may be used cautiously, but those that depress respiration should be avoided.
Management of Complications
After antibiotic therapy, high fever typically subsides within 24 hours or gradually decreases over several days. If fever recurs or persists beyond 3 days, extrapulmonary infections caused by SP, such as empyema, pericarditis, or arthritis, should be considered. Persistent fever warrants investigation for other potential causes.
Approximately 10%-20% of pneumococcal pneumonia cases are accompanied by pleural effusion. Pleural fluid should be examined and cultured as needed to determine its nature.
If empyema develops (approximately 5% of cases with inadequate treatment), active drainage should be performed to evacuate pus.