Adenovirus Pneumonia
Adenovirus pneumonia results from infection with adenoviruses (ADV), which are non-enveloped double-stranded DNA viruses. To date, at least 90 genotypes of ADV have been identified, with types 3 and 7 being the most common causes of pneumonia in children. The condition predominantly affects children aged 6 months to 2 years and is more prevalent in the winter and spring seasons. Clinically, the disease is characterized by sudden onset, prolonged high fever, severe systemic toxicity, delayed onset of rales, and radiological changes appearing earlier than physical pulmonary signs. It is prone to complications such as myocarditis and multi-organ dysfunction, with symptoms appearing in multiple systems:
- Fever: Temperatures exceeding 39°C, presenting as persistent or fluctuating fever; duration of fever can extend to 2–3 weeks.
- Severe Toxic Symptoms: Symptoms include pale or grayish complexion, listlessness, drowsiness alternating with irritability.
- Respiratory Symptoms: Persistent coughing, paroxysmal wheezing, variable degrees of dyspnea and cyanosis.
- Gastrointestinal Symptoms: Diarrhea, vomiting, and gastrointestinal bleeding.
- Neurological Symptoms: Manifestations such as drowsiness, coma, or seizures due to cerebral edema may occur.
Physical examination findings include:
- Delayed Appearance of Rales: Pulmonary rales often appear 3–7 days after the onset of high fever. Signs of consolidation may develop when pulmonary lesions coalesce.
- Hepatomegaly and Splenomegaly: Often evident due to a strong response from the mononuclear phagocyte system.
- Measles-like Rash.
- Cardiac Abnormalities: Manifestations may include tachycardia, muffled heart sounds, or signs of myocarditis and heart failure.
- Neurological Signs: Central nervous system findings such as meningeal irritation may occur.
On chest X-ray:
- Early-stage findings include increased and coarse lung markings, particularly pronounced in the mid and inner zones of both lungs.
- Between 3–7 days of illness, patchy infiltrates, often merging, become evident. In more advanced stages, larger consolidated areas may develop. The hila of the lungs may appear denser and wider, often bilaterally or more pronounced on the affected side.
- Complications such as pleural effusion, pneumothorax, mediastinal emphysema, or subcutaneous emphysema may be observed in some cases.
- A mild cardiac enlargement may be present in a small number of children.
Adenovirus pneumonia is prone to secondary bacterial infections, indicated by the following signs: persistent unremitting fever, worsening symptoms or initial improvement followed by deterioration, sputum transitioning from white to yellow purulent discharge, marked elevation of peripheral white blood cell count with a left shift, and progression of lesions or new findings on chest X-ray. Some cases of ADV pneumonia may progress to bronchiolitis obliterans (BO), leading to repeated episodes of wheezing.
Streptococcus Pneumoniae Pneumonia
Streptococcus pneumoniae pneumonia is the most common cause of bacterial pneumonia in children under 5 years of age. Streptococcus pneumoniae is a Gram-positive coccus, classified into over 100 serotypes based on differences in capsular polysaccharide antigens. In China, common serotypes include 19F, 19A, 15, 6B, 6A, and 17. Transmission occurs via airborne droplets. Additionally, as a normal commensal of the upper respiratory tract, it can spread downward when immunity is compromised or when large bacterial loads invade, leading to infection in tissues or the bloodstream.
Clinical presentations vary by age:
- In older children, Streptococcus pneumoniae pneumonia typically manifests as lobar pneumonia.
- In younger children, bronchopneumonia is more common.
The pathological changes are characterized by fibrinous exudate and alveolar inflammation, and can be classified into four stages: congestion and edema, red hepatization, gray hepatization, and resolution.
Clinically, onset is often abrupt, with possible chills and high fever reaching up to 40°C. Symptoms include tachypnea, expiratory grunts, nasal flaring, cyanosis, and possibly chest pain. Coughing is initially mild with little to no sputum, but later rust-colored sputum may appear. Mild cases maintain clear consciousness, while severe cases may exhibit restlessness, drowsiness, seizures, delirium, or even coma due to hypoxic toxic encephalopathy. Complications such as shock, acute respiratory distress syndrome (ARDS), and hemolytic uremic syndrome may occur.
Pulmonary findings:
- Early in the disease, there may be mild dullness to percussion or decreased breath sounds.
- As consolidation develops, findings may include typical dullness to percussion, increased tactile fremitus, and bronchial breath sounds.
- During the resolution phase, wet rales may be heard.
In recent years, due to the widespread use of antibiotics, symptoms have often been mild or atypical.
Chest X-ray findings lack specificity:
- In older children, diffuse lobar consolidation is more common.
- In younger children, a pattern of small lobular changes is more typical.
- Early findings may include coarse or indistinct lung markings, with progression to extensive dense shadows in one or more lung segments or lobes. During the resolution phase, scattered patchy infiltrates may remain, which typically resolve within 3–4 weeks.
- Complications such as empyema, pyopneumothorax, lung abscess, or necrotizing pneumonia may develop in some patients.
Staphylococcus Aureus Pneumonia
The causative pathogen is Staphylococcus aureus, which can invade the lungs through the respiratory tract or via hematogenous spread. Due to immature immune function, children are more susceptible to Staphylococcus aureus pneumonia, with higher incidence in neonates and infants. In 1961, Jevons first reported the isolation of methicillin-resistant Staphylococcus aureus (MRSA). Over the subsequent 20 years, MRSA gradually became one of the predominant pathogens in hospital-associated infections (hospital-associated MRSA, HA-MRSA). During the 1980s, cases of community-associated MRSA (CA-MRSA) began increasing.
The pathological changes of Staphylococcus aureus pneumonia are characterized by widespread hemorrhagic necrosis of lung tissue and the formation of multiple small abscesses. Due to the rapid progression and extensive tissue destruction, complications such as lung abscesses, empyema, pyopneumothorax, pulmonary bullae, subcutaneous emphysema, and mediastinal emphysema are frequent. Additionally, Staphylococcus aureus pneumonia may lead to sepsis and metastatic pyogenic lesions in other organs, such as purulent pericarditis, meningitis, liver abscesses, skin abscesses, osteomyelitis, and arthritis.
Clinically, the disease is characterized by acute onset, severe illness, rapid progression, and pronounced systemic toxicity. Fever often presents as a fluctuating temperature pattern, though preterm infants and debilitated children may exhibit subfebrile temperatures or no fever. Symptoms include pallor, restlessness, coughing, grunting, shallow rapid breathing, and cyanosis, with severe cases developing into shock. Gastrointestinal symptoms such as vomiting, diarrhea, and abdominal distension are also common. Pulmonary signs appear early, with scattered medium and fine moist rales in both lungs. In cases of empyema, pyopneumothorax, or subcutaneous emphysema, corresponding physical findings are observed. When mediastinal emphysema occurs, respiratory distress may worsen. Various types of rashes, such as urticarial or scarlatiniform, may also appear.
Chest X-ray findings include small patchy shadows, with lesions progressing rapidly, sometimes forming small abscesses, pulmonary bullae, or pleural effusions within hours. Serial radiographs are often necessary over a short interval. Lesion resolution is slower compared to other bacterial pneumonias, and severe cases may take up to 2 months for complete resolution. Peripheral blood tests usually show a pronounced leukocytosis with elevated neutrophils, a leftward shift of the differential, and toxic granulation. Infants and severe cases may, however, exhibit leukopenia, although the percentage of neutrophils remains high.
Mycoplasma Pneumoniae Pneumonia
Mycoplasma pneumoniae pneumonia is a common respiratory disease in children aged 5 years and older, though younger children can also be affected. The causative pathogen, Mycoplasma pneumoniae (MP), is a microorganism that lacks a cell wall and is structurally intermediate between bacteria and viruses.
The primary clinical features of Mycoplasma pneumoniae pneumonia include fever and coughing, often accompanied by headache, rhinorrhea, sore throat, and ear pain. Fever typically ranges from moderate to high. Coughing is the most prominent symptom, starting 2–3 days after the onset of illness. It initially presents as a dry cough that progresses to a persistent and severe paroxysmal cough, often with thick mucus production, occasionally streaked with blood. In some cases, the coughing resembles pertussis and can persist for 1–4 weeks.
Early pulmonary signs are often absent or minimal but may progress with the disease to include diminished breath sounds and dry or moist rales. Infants, in particular, exhibit a more acute onset, longer disease duration, and more severe symptoms such as dyspnea, wheezing, and pronounced rales compared to older children. Severe cases may develop intrapulmonary complications such as plastic bronchitis, pulmonary embolism, pleural effusion, or necrotizing pneumonia. Extrapulmonary involvement in the skin, mucous membranes, nervous system, hematologic system, and cardiovascular system may also occur, resulting in corresponding manifestations. A small subset of critically ill children may deteriorate rapidly, developing respiratory distress that requires mechanical ventilation or extracorporeal membrane oxygenation (ECMO) support, with potential fatal outcomes.
Chest X-ray findings are crucial for diagnosis, with characteristic features including:
- Bronchopneumonia.
- Interstitial pneumonia.
- Homogeneous, dense patchy shadows resembling lobar pneumonia.
- Increased perihilar opacities.
These changes can transform over time, with lesion clearance in one area accompanied by new lesions elsewhere, referred to as "migratory infiltrates". Lesions may also appear as thin, mist-like infiltrates, and pleural effusion may be observed in some cases. Discrepancies between mild clinical signs and prominent X-ray changes are a notable characteristic of Mycoplasma pneumoniae pneumonia.
Refractory Mycoplasma pneumoniae pneumonia (RMPP) may arise in cases where clinical symptoms worsen despite regular treatment with macrolide antibiotics for more than 7 days. Features of RMPP include persistent fever, severe coughing, respiratory difficulty, and worsening pulmonary imaging findings such as expanding lesions, increased density, pleural effusion, or even necrotizing pneumonia and pulmonary abscesses. Prolonged fever, persistent radiographic progression, and extrapulmonary complications are common in RMPP, particularly in older children, and the condition is often associated with multi-organ dysfunction.