bubble_chart Overview

Chlamydia pneumoniae is a newly discovered type of chlamydia that primarily causes respiratory and lung infections. In 1986, Grayeton and others identified a strain of chlamydia in students with acute respiratory infections, which was later also found in adults with respiratory diseases. Initially named the TWAR-TW strain of Chlamydia psittaci, subsequent research confirmed it as a new species and it was renamed Chlamydia pneumoniae.

bubble_chart Epidemiology

Chlamydia pneumoniae often causes upper respiratory tract and respiratory infections in children and adults. Currently, it is known that humans are the only host of this chlamydia, and transmission likely occurs through respiratory secretions between individuals. Children under 5 years old are rarely infected, while those aged 8 and above, as well as young adults, are more susceptible, especially in crowded settings such as households, schools, and military barracks. Serological epidemiological studies have confirmed that at least 40% of adults have been infected with this chlamydia, with most cases being subclinical. Elderly individuals can be reinfected.

bubble_chart Etiology

Chlamydia pneumoniae shares the same genus-specific antigens with Chlamydia psittaci and Chlamydia trachomatis, but differs in other specific antigen serological characteristics. Typically, DNA hybridization tests and restriction endonuclease analysis confirm it as a third type of Chlamydia distinct from Chlamydia trachomatis and Chlamydia psittaci.

bubble_chart Clinical Manifestations

Mild cases may have no obvious symptoms. Adolescents often present with hoarseness, dry cough, sometimes fever, sore throat, and symptoms of pharyngitis, laryngitis, sinusitis, otitis media, and bronchitis, which can persist for weeks. Pneumonia, when it occurs, is usually mild and clinically very similar to *Chlamydia pneumoniae* infection, and may be accompanied by extrapulmonary manifestations such as erythema nodosum, thyroiditis, encephalitis, and Guillain-Barré syndrome. Pneumonia in adults is often more severe, particularly in the elderly, who frequently require hospitalization and respiratory support. Some authors have found an association between *Chlamydia pneumoniae* infection and coronary heart disease through serological surveys, but this requires further confirmation. Additionally, the mechanism by which *Chlamydia pneumoniae* infection contributes to asthma is still under investigation.

Chest X-rays of *Chlamydia pneumoniae* pneumonia often show small patchy subsegmental infiltrates, with extensive consolidation seen only in severe cases. Most patients have normal white blood cell counts.

bubble_chart Diagnosis

1. Prickly-ash-like sore (trachoma) chlamydial pneumonia: In 1975, reports began to emerge of neonatal chlamydial pneumonia, which followed inclusion body purulent catarrh. This disease is often transmitted from an infected mother's pestilence, with ocular infections passing through the nasolacrimal duct into the respiratory tract. Symptoms typically appear 2–12 weeks after birth, with a slow onset. Upper respiratory infection manifestations may occur first, often without fever or occasionally with low-grade fever, followed by cough and shortness of breath. Fine moist rales or crepitations are often heard during inspiration, while expiratory wheezing is rare. Chest X-rays show bilateral widespread interstitial and alveolar infiltrates, with hyperinflation being relatively common, and occasional lobar consolidation. Peripheral white blood cell counts are generally normal, with eosinophilia. Nasopharyngeal swabs must collect epithelial cells. Direct fluorescent antibody (DFA) or enzyme immunoassay (EIA) can also be used to detect prickly-ash-like sore (trachoma) chlamydial antigens in nasopharyngeal specimens. Serological diagnostic criteria for specific antibodies include a fourfold or greater rise in paired serum antibody titers, or IgM >1:32, IgG >1:512. PCR can also be used to directly detect chlamydial DNA.

2. Psittacosis chlamydial pneumonia: This originates from contact with poultry or exposure to infected bird droppings and is an occupational disease for poultry breeders, sellers, and slaughterers. Human-to-human transmission is rare. The pathogen is excreted in secretions and feces and can remain infectious for a long time. Psittacosis chlamydia enters the human body through the respiratory tract, replicates in monocytes, and releases toxins, spreading via the bloodstream to the lungs and other tissues, causing pulmonary parenchymal and perivascular cellular infiltration, as well as hilar lymph node enlargement. The incubation period is 6–14 days, with symptoms resembling common cold, often accompanied by fever of 38–40.5°C. The initial stage of cough is dry, later becoming productive, with varying degrees of dyspnea. Other symptoms include relative moderate pulse, myalgia, chest pain, and loss of appetite, occasionally nausea and vomiting. In systemic infections, central nervous system involvement or myocarditis may occur, with rare jaundice. Hepatosplenomegaly is common, requiring differentiation from cold-damage disease and sepsis. Chest X-rays show ground-glass opacities with punctate shadows extending from the hilum to the periphery, especially in the lower lung fields. Peripheral white blood cell counts are normal, and ESR is slightly elevated early in the disease. Chlamydial inclusion bodies may be found in macrophages from alveolar exudates. Fever subsides gradually in mild cases (3–7 days), moderate cases (8–14 days), and severe cases (20–25 days). Post-infection immunity is weak, with reported recurrence rates of 21% and reinfection rates around 10%.

3. Chlamydophila pneumoniae pneumonia: The clinical manifestations of this condition are nonspecific and similar to mycoplasma pneumonia. It has a slow onset and prolonged course, with generally mild symptoms, often accompanied by pharyngitis, laryngitis, and sinusitis as characteristic features. After upper respiratory infection symptoms subside, bronchitis or pneumonia manifestations such as dry or moist rales appear. Cough may persist for over 3 weeks. White blood cell counts are normal, and chest X-rays are nonspecific, mostly showing unilateral lower lobe infiltrates as segmental pneumonia, with severe cases presenting as extensive bilateral pneumonia. Etiological testing is similar to prickly-ash-like sore (trachoma) chlamydial pneumonia, with cell culture of tracheal or nasopharyngeal aspirates testing positive for Chlamydophila pneumoniae. Alternatively, fluorescence-conjugated Chlamydophila pneumoniae-specific monoclonal antibodies can identify the pathogen in cell culture. PCR detection of Chlamydophila pneumoniae DNA is more sensitive than culture, but throat swab specimens are less ideal compared to serological detection of Chlamydophila pneumoniae-specific antibodies. Microimmunofluorescence (MIF) remains the most sensitive test for Chlamydophila pneumoniae. A specific IgM antibody titer ≥1:16, IgG ≥1:512, or a fourfold rise in antibody titer has diagnostic value.

bubble_chart Treatment Measures

The treatment principles for chlamydial pneumonia are generally similar to those for ordinary pneumonia.

1. General Treatment Pay attention to strengthening nursing care and rest, maintaining fresh indoor air, and ensuring appropriate room temperature and humidity. Keep the respiratory tract unobstructed, and frequently change positions by turning over. Dysphoria can exacerbate hypoxia, so an appropriate amount of sedatives may be administered. Provide calorie-rich foods that are rich in vitamins, easy to digest and absorb, as well as ample fluids.

2. Antibiotic Treatment

(1) Macrolide Antibiotics ① Erythromycin: Erythromycin is the first-choice antibiotic for chlamydial pneumonia, with a dosage of 50mg/(kg·d), divided into 3–4 oral doses daily for 2 weeks. For severe cases or those unable to take oral medication, intravenous administration may be used. Erythromycin reaches effective concentrations in tears and can also eliminate nasopharyngeal prickly-ash-like sore (trachoma) chlamydia, preventing the occurrence of prickly-ash-like sore (trachoma) chlamydial pneumonia. ② Roxithromycin or Rulide: The dosage is 5–8mg/(kg·d), divided into two doses taken before breakfast and dinner for 2 weeks. If cough and fatigue persist after the first course, a second course may be administered. ③ Azithromycin (Sumamed): A nitrogen-containing macrolide antibiotic with a structure similar to macrolide antibiotics. It is well absorbed orally, with a peak serum concentration of 0.4mg/L. It rapidly distributes to various tissues and organs and is highly effective against chlamydia. After treatment ends, the drug remains at therapeutic levels for 5–7 days. Its t1/2 is 12–14 hours, administered once daily, with a short treatment duration. It is excreted unchanged in bile. Administration should be spaced at least 2 hours apart from antacids. No interactions have been found with theophylline, oral anticoagulants, carbamazepine, phenytoin sodium, digoxin, etc. For children (weighing over 10kg), the first day's dose is 10mg/kg, followed by 5mg/kg daily for the next 4 days, administered once at a time, with antibacterial effects lasting at least 10 days. ④ Clarithromycin: In vitro, it is as effective as erythromycin for treating chlamydial pneumonia with lipid-based medications.

(2) Sulfisoxazole (SIZ) The dosage is 50–70mg/(kg·d), divided into 2–4 oral doses, and can be used to treat prickly-ash-like sore (trachoma) chlamydial pneumonia.

3. Supportive Treatment For patients with more severe conditions, prolonged illness, weakness, or malnutrition, fresh blood or plasma transfusions, or gamma globulin therapy should be administered to enhance the body's resistance.