Infectious pneumonia is the most common infectious disease in the neonatal period and constitutes a significant cause of neonatal mortality. Statistics indicate that the case fatality rate of perinatal infectious pneumonia is approximately 5%–20%. It may occur in utero, during delivery, or after birth and is caused by various pathogens, including bacteria, viruses, protozoa, and fungi.
Etiology
Intrauterine Infectious Pneumonia (Congenital Pneumonia)
The primary pathogens are viruses such as rubella virus, cytomegalovirus, and herpes simplex virus. These infections often arise from the mother's primary infection or the reactivation of a latent infection during pregnancy. The pathogens can infect the fetus via the bloodstream and placental barrier. Bacterial infections (e.g., Escherichia coli, Klebsiella pneumoniae), protozoal infections (e.g., Toxoplasma gondii), or mycoplasmal infections can also be transmitted to the fetus through the placenta.
Infectious Pneumonia During Delivery
Conditions such as premature rupture of membranes, prolonged labor, inadequate sterilization during delivery, maternal chorioamnionitis, or maternal genitourinary infections may lead to the fetus inhaling amniotic fluid or cervical secretions contaminated with pathogens during delivery. Common pathogens include Escherichia coli, Streptococcus pneumoniae, and Klebsiella spp., as well as viruses and mycoplasma. Prolonged labor and repeated vaginal examinations increase the risk of infection.
Postnatal Infectious Pneumonia
Respiratory Route
this occurs through contact with individuals with respiratory infections.
Hematogenous Route
This often presents as part of neonatal sepsis.
Iatrogenic Route
This results from inadequately disinfected medical devices such as incubators, nebulizers, or oxygen masks, or from transmission via healthcare workers' hands. Ventilator-associated pneumonia may also occur during mechanical ventilation. Common pathogens include Staphylococcus aureus and Escherichia coli. In recent years, infections caused by opportunistic pathogens such as Klebsiella spp., Pseudomonas aeruginosa, coagulase-negative staphylococci (CNS), and Citrobacter spp. have increased. Viruses such as respiratory syncytial virus and adenovirus are also frequently observed. Chlamydia trachomatis and Ureaplasma urealyticum should not be overlooked. Prolonged use of broad-spectrum antibiotics can lead to fungal infections.
Clinical Manifestations
Intrauterine Infectious Pneumonia
Clinical manifestations vary widely. Symptoms typically appear within the first 24 hours of life. Many newborns have a history of asphyxia at birth and exhibit tachypnea, grunting, cyanosis, respiratory distress, unstable body temperature, and reduced reactivity after resuscitation. Lung auscultation may reveal coarse or diminished breath sounds, or crackles. Severe cases may develop respiratory failure, heart failure, disseminated intravascular coagulation (DIC), shock, or persistent pulmonary hypertension of the newborn (PPHN). In cases of viral infections, symptoms may not be apparent at birth but may emerge gradually after 2–3 days, or even around 1 week, with progressive respiratory distress that can lead to bronchopulmonary dysplasia in later stages. Peripheral blood leukocyte counts are often normal but may decrease or increase. Elevated umbilical cord blood IgM levels (>200–300 mg/L) or specific IgM can aid in the diagnosis of intrauterine infection. Chest X-rays often show no changes on the first day for viral pneumonia but reveal interstitial pneumonia changes after 24 hours. Bacterial pneumonia typically presents as bronchopneumonia on imaging.
Infectious Pneumonia During Delivery
Symptom onset varies depending on the pathogen, usually occurring several days to weeks after birth. Bacterial infections often begin within 3–5 days after birth, while type 2 herpes simplex virus infections manifest between 5–10 days of life. Chlamydia trachomatis infections have an incubation period of 3–12 weeks. Diagnostic evidence can be obtained by smears, cultures, and PCR testing of blood samples or tracheal secretions collected after birth.
Postnatal Infectious Pneumonia
Systemic symptoms include fever or hypothermia and reduced responsiveness. Respiratory symptoms include tachypnea, nasal flaring, cyanosis, frothy secretions, and intercostal or suprasternal retractions. Early lung signs are often subtle but may include fine crackles in both lungs during the disease course. Respiratory syncytial virus pneumonia can present with wheezing, accompanied by wheezing sounds on lung auscultation. Chlamydia trachomatis pneumonia commonly occurs in neonates with a history of conjunctivitis. Staphylococcus aureus pneumonia tends to complicate with empyema or pneumothorax. Nasopharyngeal secretions can be cultured for bacteria, viruses can be isolated, and fluorescent antibody tests or serum-specific antibody assays assist in identifying pathogens. Chest X-ray changes vary depending on the causative pathogen. Bacterial pneumonia often shows diffuse, patchy opacities in both lungs with uneven density. Staphylococcus aureus infections with pleural effusion, pneumothorax, or pulmonary bullae exhibit corresponding radiographic findings. Viral pneumonia mainly shows interstitial changes, hyperinflation, and emphysema.
Treatment
Airway Management
Measures include nebulized inhalation, positional drainage, regular turning, chest percussion, and timely suctioning of oropharyngeal and nasal secretions to maintain airway patency.
Maintaining Normal Blood Gases
Supplemental oxygen is administered based on clinical needs and blood gas analysis using nasal cannulas, face masks, or nasal continuous positive airway pressure (nCPAP) to maintain blood gas levels within the normal range. Mechanical ventilation is required when hypercapnia cannot be corrected.
Anti-Pathogen Therapy
Antibiotic selection for bacterial pneumonia can refer to the section on neonatal sepsis. Chlamydia trachomatis pneumonia is treated with erythromycin. Acyclovir is used for herpes simplex virus pneumonia, and ganciclovir is prescribed for cytomegalovirus pneumonia.
Supportive Therapy
Measures include correction of circulatory disturbances, water and electrolyte imbalances, and acid-base disorders. Intravenous fluids should be administered slowly to avoid heart failure and pulmonary edema. Adequate energy and nutritional support are critical, and intravenous immunoglobulin may be administered as needed to enhance immune function.