bubble_chart Overview

The surface of the lungs is exposed to many pestilent substances. If the defense mechanisms of the respiratory tract are weakened, it is easy to become infected and develop bacterial pneumonia. The lung's defense functions include the epiglottic reflex, which prevents the inhalation of infected secretions; ciliary movement, which is used to clear respiratory epithelial cells carrying microorganisms; the cough reflex, which expels foreign bodies and mucus from the lower respiratory tract (attached to airborne microorganisms); lymphatic vessels, which drain the contents of terminal bronchioles and bronchioles; and phagocytes, which clear alveolar microorganisms. Viral infections can damage these defense mechanisms, often occurring several days before the onset of bacterial pneumonia. Since the 1950s, China has made remarkable achievements in the research of viral pneumonia. However, there is still insufficient understanding of bacterial pneumonia. This indicates that the exact incidence and pathogen spectrum of bacterial pneumonia in China require further study. The etiological diagnosis of bacterial pneumonia in children deserves attention.

bubble_chart Etiology

Staphylococcus aureus pneumonia is a type of pneumonia caused by Staphylococcus aureus (usually coagulase-positive). Due to the overuse of antibiotics, strains of Staphylococcus aureus resistant to medicinal properties have significantly increased, leading to a rise in Staphylococcus aureus infections. This disease often complicates staphylococcal sepsis and is more common in infants and newborns, although older children can also be affected. It is more prevalent during the winter and spring seasons when the incidence of upper respiratory infections is higher. Cross-infections often occur in hospitals or nurseries, leading to outbreaks. Staphylococcus aureus can produce various toxins and enzymes, such as hemolysins, staphylokinase, and coagulase. It is generally believed that coagulase is related to bacterial virulence. If the bacteria are coagulase-negative (such as Staphylococcus epidermidis), they are often opportunistic pathogens and rarely cause severe diseases, but they are one of the common bacteria causing hospital-acquired infections. Penicillin G-resistant Staphylococcus aureus has become a global problem, and in the 1980s, reports from both domestic and international sources indicated that methicillin-resistant Staphylococcus aureus (MRSA) had become a major pathogen in hospital-acquired infections.

bubble_chart Pathological Changes

Primary bronchopneumonia caused by Staphylococcus aureus is characterized by extensive hemorrhagic necrosis and multiple small abscesses. The pleural surface of the lungs is covered with a thick layer of fibrinous purulent exudate. The abscesses contain Staphylococcus aureus, white blood cells, red blood cells, and necrotic tissue debris. If the small abscesses beneath the pleura rupture, empyema or pyopneumothorax may form. Sometimes, the infection can erode the bronchi, leading to bronchopleural fistula. If it occurs secondary to sepsis, abscesses may develop not only in the lungs but also in other organs such as subcutaneous tissue, bone marrow, heart, kidneys, adrenal glands, and brain.

bubble_chart Clinical Manifestations

1. Symptoms and Signs: Staphylococcus aureus pneumonia is commonly seen in infants under 1 year old. After 1-2 days of upper respiratory tract infection or several days to a week of skin pustules, a sudden high fever appears. Older children mostly have remittent high fever, but newborns may have low fever or no fever. Pneumonia develops rapidly, manifesting as increased respiratory and heart rates, moaning, cough, cyanosis, etc. Sometimes, there may be scarlet fever-like rashes and gastrointestinal symptoms such as vomiting, diarrhea, abdominal distension and fullness (due to toxic intestinal paralysis). The child may be drowsy or dysphoric, and in severe cases, convulsions may occur. Toxic symptoms are often more pronounced, even presenting as shock. Lung signs appear early, with reduced breath sounds and scattered moist rales in the early stages. During the progression, lung abscesses rapidly develop, often as scattered small abscesses. Empyema and pyopneumothorax are characteristic of this condition. When complicated by empyema or pyopneumothorax, there is dullness on percussion, decreased or absent vocal fremitus, and breath sounds.

2. X-ray Examination: ① Clinical symptoms are inconsistent with chest X-ray findings. When pneumonia first starts, clinical symptoms are already severe, but X-ray signs are minimal, only showing increased lung markings and small infiltrates on one or both sides; when clinical symptoms are improving, chest X-rays may show significant lesions such as lung abscesses and bullae. ② The disease progresses rapidly, and small inflammatory lesions can develop into abscesses within hours. ③ During the course of the disease, small abscesses, pyopneumothorax, and bullae are often present. Severe cases may also be complicated by pneumomediastinum, subcutaneous emphysema, and bronchopleural fistula. ④ The duration of lesion shadows on chest X-rays is longer than that of general bacterial pneumonia, and shadows may still not completely disappear after about 2 months.

bubble_chart Auxiliary Examination

White blood cells are generally elevated above 15×10⁹～30×10⁹/L (15000～30000), with an increase in neutrophils, and toxic granules may appear within the white blood cells. In half of the young infants, it may decrease to below 5×10⁹/L (5000), while the percentage of neutrophils remains relatively high. A decrease in the total white blood cell count often indicates a severe prognosis. C-reactive protein is elevated. A positive bacterial culture of tracheal cough or aspirate and thoracentesis fluid has diagnostic significance.

bubble_chart Diagnosis

Early-stage Staphylococcus aureus pneumonia is often difficult to recognize. The disease should be considered when symptoms of pneumonia develop rapidly. A recent history of upper respiratory tract infection, minor skin abscesses, or mastitis in a nursing mother can aid in the diagnosis.

bubble_chart Treatment Measures

The general treatment for this disease is the same as for bronchopneumonia. Since the condition is often more severe, aggressive treatment should be initiated early when staphylococcal pneumonia is suspected to control the infection. Penicillin can be administered at 100,000 to 500,000 U/(kg·d), either intramuscularly or intravenously. For penicillin G-resistant staphylococcal pneumonia, drugs such as oxacillin (P12), cloxacillin, methicillin, erythromycin, chloramphenicol, bacitracin, rifampin, vancomycin, and lincomycin can be used. Additionally, cephalosporins can be used, with the first generation such as cefazolin and cephalothin being more effective against resistant staphylococci than the second and third generations. The former can be administered intramuscularly or intravenously at a dose of 20-30 mg/kg per day, which can be increased to 50-100 mg/kg per day for severe cases; the latter is administered intravenously at 50-150 mg/kg per day. For methicillin-resistant staphylococcal infections, vancomycin and its new derivative teicoplanin should be used. Generally, antibiotics can be discontinued 7 days after the body temperature returns to normal and most lung signs disappear, with a treatment course of at least 3-4 weeks. When developing into empyema or pyopneumothorax, if the amount of pus is small, repeated thoracentesis for pus drainage can be used; however, in most children, the pus increases rapidly and is too viscous to be easily aspirated, so closed drainage should be performed. The efficacy of intrapleural antibiotic injection is uncertain.

bubble_chart Prognosis

Concurrent Staphylococcus aureus meningitis and pericarditis or infantile tension pneumothorax have a severe prognosis, with a mortality rate as high as 10-20%. Complications such as empyema and pyopneumothorax have a better prognosis, and cured patients show no long-term pulmonary dysfunction upon follow-up.

bubble_chart Prevention

In addition to the preventive measures outlined in the pneumonia overview, it is essential to prioritize the cleanliness and hygiene of living spaces in childcare facilities. Regular checks should be conducted to determine if staff members are carriers of pathogens, and appropriate measures should be taken promptly for those who are identified as carriers.

bubble_chart Differentiation

Staphylococcus aureus pneumonia must be differentiated from the following diseases: Streptococcus pneumoniae, Haemophilus influenzae, or Klebsiella pneumoniae pneumonia, primary pulmonary subcutaneous nodules with cavity formation or caseous pneumonia, secondary lung abscess due to tracheal foreign body, and diaphragmatic hernia. The characteristic features on X-ray, such as lung abscess, bullous lung emphysema, and empyema or pyopneumothorax, can serve as diagnostic evidence for Staphylococcus aureus pneumonia; however, it must be differentiated from empyema and pyopneumothorax caused by other bacterial pneumonias. Therefore, etiological diagnosis is crucial.