| disease | Mycoplasma Pneumoniae Pneumonia |
| alias | Mycopeasmae Pneumonia |
Mycoplasma pneumoniae pneumonia refers to acute respiratory infection accompanied by pneumonia caused by Mycoplasma pneumoniae. It accounts for about 10% of all infectious pneumonias or more than one-third of non-bacterial pneumonias. It can occur in all age groups but is more common in children and young adults, with a higher incidence in autumn and winter. It usually appears sporadically but can also cause small outbreaks in densely populated areas.
bubble_chart Etiology
There are more than ten species of Mycoplasma, only Mycoplasma pneumoniae is pathogenic to humans. It was identified by Chanock in 1961, can be cultured artificially, lacks a cell wall, and under a light microscope, its colonies appear round with a thick, granular center and a flat periphery with a transparent zone, resembling a fried egg. It is transmitted through airborne droplets from oral and nasal secretions.
After invading the respiratory tract, Mycoplasma can cause pharyngitis and spread to the trachea, bronchi, and lungs, growing between the ciliated epithelial cells of the respiratory tract. The nature of its disease lies in the production of peroxides that damage airway mucosal cells, and it may also be related to the body's allergic reaction to Mycoplasma metabolic products.
The infection begins in the upper respiratory tract, often with pharyngeal congestion and sometimes accompanied by tympanic membrane inflammation. The basic pathological changes include suppurative bronchiolitis and interstitial pneumonia, with bronchial mucosal congestion and edema, infiltration of mononuclear cells and lymphocytes, possible necrosis and shedding of epithelial cells, infiltration of neutrophils and mononuclear cells in alveolar walls and interstitial spaces, and a small amount of inflammatory exudate in the alveoli, which may coalesce into focal consolidation, forming bronchopneumonia or lobular interstitial pneumonia. In some cases, it may invade the pleural membrane, leading to fibrin exudation and a small amount of pleural effusion.
bubble_chart Clinical ManifestationsSystemic symptoms: Precursory symptoms such as rhinitis and pharyngitis often occur before the onset of illness. The onset is generally mild, and some cases (about 1/3) may show no obvious symptoms and are only detected during chest X-rays. Grade II fever is common, with a few cases presenting high fever but generally no shivering. Symptoms include lack of strength, poor appetite, and muscle pain. Headache is common and sometimes severe, worsening with cough.
Respiratory symptoms: Persistent and severe cough is a prominent symptom, possibly accompanied by a small amount of sticky sputum, which may sometimes be mucopurulent or bloody. Since the pathogen can survive for a long time in the airway mucosal epithelium, affecting ciliary activity, the cough may persist for a period even after the fever subsides. Substernal pain may occur, but chest pain is rare. In cases with extensive lesions, dyspnea and cyanosis may appear.
Signs: There may be swelling and tenderness of the cervical and submandibular lymph nodes. A few cases may present with skin maculopapules or herpes labialis, and some may exhibit a relatively moderate pulse. Pulmonary signs are often not obvious, with generally no signs of lung consolidation. There may be localized diminished breath sounds and a few dry or moist rales.
bubble_chart Auxiliary Examination
Most patients have normal peripheral white blood cell counts, with a few showing an increase, and some exhibit an accelerated erythrocyte sedimentation rate. Approximately two-thirds of cases test positive for red blood cell cold agglutinin (titer >1:32), with the highest positivity rate occurring between weeks 2 and 6. A progressively rising titer is particularly helpful for diagnosis. The advantage of this test is its simplicity and ease of performance, though it is retrospective and lacks specificity. Between 40% and 60% of patients test positive for Streptococcus MG antibodies (1:40–1:80), which serves as an important diagnostic criterion for this disease. Sputum or nasopharyngeal swab cultures grown on agar medium containing horse serum and yeast can yield Mycoplasma pneumoniae.
In addition to general systemic infectious manifestations, most patients experience headache, sometimes severe and persistent, along with a stubborn, irritating cough. There is a dissociation between signs and X-ray findings, meaning that while X-rays show significant pulmonary infiltrative shadows, clinical signs are minimal or absent. A positive cold agglutinin test, especially with a progressively increasing titer, and a positive streptococcus MG antibody test hold significant diagnostic value. The growth of Mycoplasma pneumoniae in cultures of sputum or nasopharyngeal swabs confirms the diagnosis.
bubble_chart Treatment Measures
General treatment and nursing care are the same as for bacterial pneumonia. The antibiotic of choice is erythromycin, with a dosage of 0.3g orally four times daily for mild cases, or 1.0–1.5g/d intravenously for more severe cases. Tetracycline at 0.5g orally four times daily may also be used. The usual course of treatment is 10–14 days and may be combined with Chinese medicinals that clear heat and remove toxins. For severe cough, codeine phosphate 15–30mg may be administered.
The disease follows a benign course, with most cases recovering after about two weeks of effective treatment. However, severe complications can prolong the course of the illness.
The principle is to prevent common cold and isolate patients. Since the patient's nasopharyngeal secretions and sputum can spread through airborne droplets, they should be isolated until symptoms disappear, and indoor disinfection should be carried out.
This disease is a benign condition with few complications. In children, it may be complicated by otitis media and tympanitis, and in rare cases by meningitis and pleuritis. Due to the action of cold agglutinins, it can cause neurological damage such as optic disc edema, disorientation, unconsciousness, and transverse myelitis, as well as complications like acute hemolysis, thrombocytopenia, and Raynaud's phenomenon.
This disease should be differentiated from viral pneumonia, eosinophilic pulmonary infiltration, Legionella pneumonia, and infiltrative pulmonary subcutaneous nodules.
