| disease | Mycoplasma Pneumonia |
| alias | Mycoplasma Pneumonia, Mycoplasma Pneumonia |
Mycoplasma pneumonia is an acute respiratory infection accompanied by pneumonia caused by Mycoplasma pneumoniae. Among the pathogens previously referred to as "primary atypical pneumonia," Mycoplasma pneumoniae is the most common. It can cause epidemics, accounting for about 10% of all types of pneumonia, and severe cases of Mycoplasma pneumonia can also lead to death.
bubble_chart Pathogen
Mycoplasma pneumoniae is the smallest microorganism capable of independent life, situated between bacteria and viruses, with a size of 200nm. It lacks a cell wall and only has a cell membrane composed of three layers, often confused with the L-form of bacteria due to their similar colonies. It can grow and reproduce by division in cell-free culture media, contains RNA and DNA, generates energy through metabolism, and is sensitive to antibiotics. Mycoplasma is a pathogen for various animal diseases, with eight types currently identified, among which only Mycoplasma pneumoniae is confirmed to cause disease in humans, primarily respiratory diseases. It grows well on agar media containing 20% horse serum and yeast, initially forming typical dome-shaped mulberry fruit-like colonies visible under a microscope, which turn into fried egg shapes after multiple passages. Mycoplasma ferments glucose, exhibits hemadsorption, lyses red blood cells of guinea pigs and sheep, and is resistant to methylene blue, thallium acetate, penicillin, etc. Serum identification is ultimately required. It is transmitted through air via oral and nasal secretions, causing sporadic and small outbreaks of respiratory infections, mainly seen in children and adolescents, but now also not uncommon in adults, with more cases in autumn and winter. Respiratory infections include pharyngitis and bronchitis, with a few affecting the lungs. Mycoplasma pneumonia accounts for more than one-third of non-bacterial pneumonias or about 10% of all pneumonias.
bubble_chart PathogenesisMycoplasma pneumoniae can be found in respiratory secretions from 2-3 days before the onset of the disease until several weeks after recovery. It spreads through contact, residing between ciliated epithelial cells without invading lung tissue. Its cell membrane contains neuraminic acid receptors, allowing it to adhere to the surface of the host's respiratory epithelial cells, inhibiting ciliary activity and damaging epithelial cells, while also producing hydrogen peroxide to further cause local tissue injury. The pathogenic nature of the disease may be related to the patient's allergic reaction to the pathogen or its metabolites. Infection triggers humoral immunity, and since most adults already have antibodies in their serum, the disease rarely manifests.
bubble_chart Pathological Changes
The pulmonary lesions present as patchy or confluent bronchopneumonia or interstitial pneumonia, accompanied by acute bronchitis. Alveoli may contain a small amount of exudate, and focal atelectasis, lung excess changes, and lung qi swelling may occur. The alveolar walls and septa are infiltrated with neutrophils and large mononuclear cells. Bronchial mucosal cells may show necrosis and shedding, with neutrophil infiltration. The pleural membrane may exhibit fibrin exudation and a small amount of effusion.
bubble_chart Clinical Manifestations
The incubation period is 2-3 weeks, with a slow onset, and about one-third of cases are asymptomatic. It manifests in forms such as bronchitis, pneumonia, otitis media, etc., with pneumonia being the most severe. Initial symptoms include lack of strength, headache, sore throat, chills, fever, muscle aches, loss of appetite, nausea, vomiting, etc., with headache being prominent. Fever varies in intensity and can reach up to 39°C. After 2-3 days, significant respiratory symptoms appear, such as paroxysmal irritating cough, coughing up small amounts of sticky or mucopurulent sputum, sometimes with blood in the sputum. Fever can persist for 2-3 weeks. After the fever subsides, a cough may remain, accompanied by substernal pain, but no chest pain.
The condition is generally mild, sometimes severe, but rarely fatal. Fever lasts from 3 days to 2 weeks, and cough can extend to about 6 weeks. There is a 10% recurrence rate, with pneumonia occurring in the same lobe or the same lobe. A few patients have a cold agglutinin titer of more than 1:500. There may be considerable intravascular hemolysis, which often occurs during fever reduction or when catching a cold.
Very few cases may be accompanied by central nervous system symptoms, such as meningitis, meningoencephalitis, polyradiculitis, and even mental disorders. Hemorrhagic otitis media, gastroenteritis, arthritis, thrombocytopenic purpura, hemolytic anemia, pericarditis, myocarditis, and hepatitis have also been reported.
bubble_chart Auxiliary Examination
X-ray examination: Pulmonary lesions present with diverse manifestations. Early interstitial pneumonia shows increased lung markings and reticular shadows, which later develop into patchy or uniform hazy shadows, deeper near the hilum and more frequent in the lower lobes. About half are distributed in a single lobe or lung segment, sometimes with extensive infiltration and consolidation. Enlarged hilar lymph nodes can be seen in children. A small number of cases have a small amount of pleural effusion. Pneumonia usually resolves within 2-3 weeks, occasionally extending to 4-6 weeks.
Culture of sputum, nasal, and throat swabs can yield Mycoplasma pneumoniae, but it takes about 3 weeks, and its growth can be inhibited by antiserum, or confirmed by hemolysis of red blood cells in negative cultures. About half of the cases produce antibodies 2 weeks after onset. The red blood cell cold agglutination test is positive, with a titer of 1:32 or higher, and a fourfold increase in titer during the convalescence stage is significant. The streptococcal MG agglutination test is positive in 40-50% of cases, with MG streptococcal agglutinins appearing in the blood at a titer of 1:40 or higher, and a gradual fourfold increase in titer is more significant. Specific antibodies in serum can be measured by complement fixation test, metabolic inhibition test, indirect hemagglutination test, indirect immunofluorescence, and enzyme-linked immunosorbent assay. These are all helpful for diagnosis. Detection of Mycoplasma pneumoniae DNA by PCR in specimens such as throat swabs and bronchoalveolar lavage fluid has been reported domestically, with high specificity and sensitivity, and can be used for early diagnosis. The diagnostic value of anti-Mycoplasma pneumoniae monoclonal antibody technology is still under investigation.
Clinical symptoms such as headache, lack of strength, myalgia, nasopharyngeal lesions, cough, chest pain, purulent sputum, and bloody sputum, along with lung X-ray findings and laboratory tests such as cold agglutination tests, aid in diagnosis.
I. History and Symptoms:
The onset is relatively slow, with most cases presenting as pharyngitis or bronchitis, and 10% as pneumonia. Main symptoms include shivering, fever, lack of strength, headache, general discomfort, irritating dry cough accompanied by sticky sputum, purulent sputum, or even bloody sputum. Severe cases may experience shortness of breath and chest pain during intense coughing. Other possible symptoms include nausea, loss of appetite, vomiting, diarrhea, as well as arthralgia, myocarditis, pericarditis, hepatitis, peripheral neuritis, meningitis, and skin papules as extrapulmonary manifestations.
II. Physical Examination Findings:
Nasopharyngeal and conjunctival congestion and edema may be present, along with possible cervical lymphadenopathy and rash. Chest signs are often not prominent, but fine moist rales may be heard on lung auscultation, and occasionally pleural friction rubs and signs of pleural effusion may be noted.
III. Auxiliary Examinations:
(1) Chest X-ray: Increased lung markings, with possible polymorphic infiltrates, more commonly in the lower lobes, which may appear as speckled, patchy, or uniformly hazy shadows. Approximately 1/5 of cases may show a small amount of pleural effusion.
(2) Etiological Examination: Isolation of Mycoplasma pneumoniae is difficult to widely apply and is not helpful for early diagnosis.
(3) Serological Examination: A serum pathogen antibody titer >1:32, streptococcal MG agglutination test titer ≥1:40 is considered positive. A fourfold or greater increase in titer on two consecutive tests has diagnostic value. Indirect serum tests >1:32, indirect fluorescent tests >1:66, indirect immunofluorescence for Mycoplasma pneumoniae IgG >1:16, IgM >1:8, and avidin enzyme-linked immunosorbent assays can directly detect Mycoplasma pneumoniae antigens, with results available within 24 hours, all of which have diagnostic significance.
bubble_chart Treatment Measures
Erythromycin, josamycin, and tetracyclines are effective in treatment and can shorten the course of the disease. Erythromycin 0.5g, every 8 hours; josamycin has mild gastrointestinal reactions and fewer other side effects, with efficacy similar to erythromycin, dosage 1.2～1.8g/d, taken orally in divided doses; tetracycline 0.5g, every 6 hours. Treatment should continue for 2～3 weeks to avoid recurrence. For severe cough, codeine 15～30mg can be used, three times a day.
The preventive effect of mycoplasma vaccine is still inconclusive, and intranasal administration of live attenuated vaccine has a certain preventive effect.
It should be differentiated from infiltrative pulmonary subcutaneous nodules, viral pneumonia, bacterial pneumonia, and other conditions.
