Mycoplasma pneumonia

Introduction to mycoplasmal pneumonia Mycoplasmal pneumonia (mycoplasmal pneumonia) is a pneumonia caused by mycoplasmal pneumonia (MP). It has been called primary atypical pneumonia (primaryatypical pneumonia), slow onset, fever, paroxysmal irritating cough, a small amount of mucous or mucus Purulent sputum (occasionally bloody), lung signs are not obvious, but easy to cause extra-pulmonary involvement, can also threaten life or death, occur in children or adolescents, accounting for about 15% to 30% of the total number of pneumonia, The prevalence can be as high as 40% to 60%; the general prognosis is good and it is a self-limiting disease. basic knowledge The proportion of illness: 0.02% Susceptible people: old people, children Mode of transmission: airborne Complications: meningitis hemolytic anemia pericarditis myocarditis

Mycoplasma pneumonia

Causes

Mycoplasma infection (40%):

Mycoplasma passes through the mucociliary layer on the mucosal surface of the host respiratory tract and adheres to the mucosal epithelial cells. This adhesion is related to the terminal structure of the P1 protein on the surface of Mycoplasma pneumoniae. When this adhesion factor is attached to the airway mucosal epithelial cells, the release of toxic metabolites can lead to decreased ciliary movement and cell damage.

Environmental factors (30%):

In China, pediatric pneumonia is distributed in four seasons, but it occurs mostly in the winter or winter and spring seasons or in the season of sudden changes in climate and frequent colds. In the south, there are also small peaks in the summer or summer and autumn. Air pollution, crowded rooms, poor ventilation in the house are the external environmental causes of pneumonia in children, and various respiratory infections, diarrhea in children, malnutrition, anemia, rickets, etc. can all be intrinsic factors in children with pneumonia. The condition is often heavier and the course of disease is longer, which is easy to become a procrastination.

Pathogenesis

It is believed that its pathogenesis is mainly due to the adhesion of mycoplasma through the mucociliary layer of the mucosal surface of the host respiratory tract to the mucosal epithelial cells. This adhesion is related to the terminal structure of the P1 protein on the surface of Mycoplasma pneumoniae. When this adhesion factor is attached to the respiratory mucosa In epithelial cells, the release of toxic metabolites can lead to decreased ciliary movement and cell damage.

After infection with Mycoplasma pneumoniae, it can cause humoral immunity and cellular immune response. The humoral immune response first appears specific IgM antibody, and then IgG antibody appears. For a long time, the secretory IgA antibody produced locally in the nasopharynx can effectively inhibit pneumonia. Mycoplasma binds to the respiratory epithelium. The respiratory IgA antibody is more directly related to the immune status of the host antibody in serum. Local antibody is very important in infection defense. Local immunity in addition to IgA, local cellular immunity also plays a role, because the initial infection makes Sensitization in young children causes a heavier clinical manifestation of reinfection, indicating a relationship between the disease and hypersensitivity in the body after infection with Mycoplasma pneumoniae.

The pathological changes were mainly bronchitis, bronchiolitis and interstitial pneumonia, wall edema, thickening, infiltrating plaque, mucus and even purulent secretions in the bronchi and bronchioles. Microscopic bronchitis was shown under the microscope. There is interstitial pneumonia, a small amount of edema fluid and macrophages can be seen in the alveoli, edema in the bronchioles, hyperemia and infiltration of monocytes and lymphocytes, neutrophils, exfoliated epithelial cells and cell debris can be seen in the cavity. Lymphocytes and mononuclear cells infiltrated in the adjacent alveolar septum, and diffuse alveolar necrosis and hyaline membrane lesions were severely observed.

Mycoplasma pneumonia prevention

Usually, we should do a good job in prevention of mycoplasmal pneumonia in children. Some experts remind that children should pay attention to physical exercise, often carry out outdoor activities, and open windows to ventilate the body, so that the body's cold tolerance and adaptability to changes in environmental temperature are enhanced. Increase or decrease clothes to avoid contact with children with respiratory infections. In the epidemic season of respiratory infections, do not bring children to public places, rationally mix nutrition, give children oral calcium and vitamin AD early, and soak the sun. The predisposing factors of pneumonia also contribute to the prevention of pneumonia, vaccination on time, but also do not picky eaters, not partial eclipse, adequate rest and adequate sleep.

Mycoplasma pneumonia complications Complications meningitis hemolytic anemia pericarditis myocarditis

The condition is usually mild, sometimes it can be heavy, but it rarely dies. The fever can be extended from 3 days to 2 weeks. The cough can be extended to about 6 weeks. There may be intravascular hemolysis. Hemolysis is often seen in fever or when it is cold.

Very few cases can be associated with central nervous system symptoms, such as meningitis, meningoencephalitis, radiculitis, and even mental disorders, hemorrhagic tympanitis, gastroenteritis, arthritis, thrombocytopenic purpura, hemolytic anemia , pericarditis, myocarditis, hepatitis have also been found.

Symptoms of mycoplasmal pneumonia Common symptoms: weak nasal congestion, shortness of pus, sore throat, loss of appetite, bronchoalveolar sound, lung texture, muscle sore rash

The incubation period is 2 to 3 weeks, the onset is slow, and about 1/3 of the cases are asymptomatic. It occurs in the form of branch tube-bronchitis, pneumonia, ear tympanitis, etc., and is most severe with pneumonia. At the beginning of the onset, there was fatigue, headache, sore throat, chills, fever, muscle aches, loss of appetite, nausea, vomiting, etc., and headaches were significant. The fever varies and can be as high as 39 °C. After 2 to 3 days, obvious respiratory symptoms, such as paroxysmal irritating cough, coughing a small amount of sticky or mucopurulent sputum, sometimes with blood in the sputum. The fever can last for 2 to 3 weeks. After the heat returns to normal, there is still a cough, accompanied by pain under the chest, but no chest pain.

Physical examination showed mild nasal congestion, runny nose, and moderate pharyngeal congestion. The eardrum is often congested, and about 15% have tympanitis. The cervical lymph nodes can be swollen. A few cases have maculopapular rash, erythema or cold sore. There are no obvious abnormal signs in the chest, about half of which can be dry or wet rales, and a small amount of pleural effusion occurs in about 10% to 15% of cases.

The condition is generally mild, sometimes heavier, but rarely dies. After 3 days to 2 weeks of fever, the cough can be extended to about 6 weeks. There is 10% recurrence, pneumonia is found in the same lobe or the same lobe, and a small number of patients have a titer of erythrocyte condensation titer above 1:500. / There may be considerable intravascular hemolysis, hemolysis is often seen in the case of fever, or when it is cold.

Very few cases can be associated with central nervous system symptoms, such as meningitis, meningoencephalitis, frequent radiculitis, and even mental disorders. Hemorrhagic ear tympanitis, gastroenteritis, arthritis, thrombocytopenic purpura, hemolytic anemia, pericarditis, myocarditis, and hepatitis have also been found.

Examination of mycoplasmal pneumonia

Blood picture

The total number of white blood cells is often in the normal range, but occasionally it can be increased. In 25% of patients, leukocytes exceed 10.0×109/L, and a few can reach (25.0-56.0)×109/L, classified as neutrophils or eosinophils. Slightly increased, thrombocytopenia, direct coombs test can be positive, ESR can increase in the early stages of the disease.

2. Culture method

Due to the high nutritional requirements of Mycoplasma pneumoniae and slow growth, it needs to be observed for 10 to 30 days or more, which is of little help to clinical diagnosis. At present, the foreign disease control center (CDC) recommended Hayflied medium is still used abroad, and the domestic multi-purpose capital pediatric research So Martin medium or porcine lung digestive-based medium.

3. Serological methods

Complement binding test: It is a serological diagnosis method widely used for the diagnosis of Mycoplasma pneumoniae infection. The serum titer of the acute phase and the recovery period is increased by 4 times, or the single serum titer 1:32 is judged as yang. Sensitivity is up to 90%, specificity is 94%, positive only in the first infection, and no positive reaction in reinfection.

Indirect hemagglutination test: mainly detect IgM antibody, which is positive 7 days later, peaks at 10 to 30 days, gradually decreases from 12 to 26 weeks, blood collection should be early in the acute phase, otherwise it is not easy to detect 4 times increased antibody, the specificity is not yet Ideal, similar to the patch test.

Condensation set test: It is a non-specific test for the diagnosis of Mycoplasma pneumoniae infection, 33% to 76% of infected people are positive (potency 1:32), the higher the titer, the more likely the disease is, often in the onset A positive reaction occurs on the first weekend or the second week, lasting about 2 to 4 months. This test may also have a false positive reaction in pneumonia and respiratory infections caused by adenovirus, parainfluenza virus, etc. in infants and young children.

4. Nucleic acid hybridization test

Detection of Mycoplasma pneumoniae using a nucleic acid probe technique labeled with a radioisotope (32P, 125I, etc.). Although this method has high sensitivity and specificity, it requires high conditions and requires the use of isotopes, so it is difficult to promote it in the clinic.

5. Polymerase chain reaction (PCR)

Since 1992, the method used to check the clinical specimens of Mycoplasma pneumoniae infection. From the comprehensive results, the positive rate of PCR detection is significantly higher than that of the culture method (sensitivity is 10 to 100 times higher than that of common culture methods), and is also significantly higher than serology. Hybridization method with probe, its specificity is also strong, no cross-reaction with other mycoplasma, and is not interfered by other bacteria in the mouth, and the time required is short. Therefore, PCR method can be used for early diagnosis to guide clinical rational drug use. In the central nervous system, rapid and reliable diagnosis is more necessary. Because this method is quite sensitive, special care should be taken during the operation to avoid contamination.

6. X-ray examination of the lungs

Visible cloud-like or uniform shadows, the near-lung door is denser, the outward is gradually shallower, the edge is not clear, usually does not invade the whole leaf, the vast majority is a leaf affected, the following leaves are more common, the lower left is the most, right Next time, about 20% of the lateral position has a small amount of pleural effusion, about 10% of the atelectasis, occasionally pleurisy, lung lesions usually absorb in 2 to 3 weeks, complete absorption takes 4 to 6 weeks, children about 30% With hilar lymphadenopathy.

Diagnosis and diagnosis of mycoplasmal pneumonia

diagnosis

Clinical symptoms such as headache, fatigue, myalgia, nasopharyngeal lesions, cough, chest pain, purulent sputum and blood stasis, lung X-ray findings and laboratory tests such as condensation test can help diagnose.

First, medical history, symptoms:

The onset is slower, most of them are pharyngitis and bronchitis, and 10% are pneumonia. Symptoms mainly include chills, fever, fatigue, headache, general discomfort, irritating dry cough, accompanied by sticky phlegm, purulent sputum, and even blood stasis. In severe cases, there may be shortness of breath, chest pain during coughing, nausea, loss of appetite, vomiting. , diarrhea and joint pain, myocarditis, pericarditis, hepatitis, peripheral neuritis, meningitis, skin macules and other extrapulmonary manifestations.

Second, physical examination found:

Nasopharyngeal and conjunctival hyperemia, edema, may have cervical lymphadenopathy, rash; chest signs are not obvious, lung auscultation may have fine wet rales, occasional pleural friction sound and pleural effusion.

Third, auxiliary inspection:

(1) X-ray chest radiograph, for the increase of lung texture, the lung parenchyma may have a multi-form infiltration shape, the following leaves are more common, but also, spotted, patchy or evenly blurred shadow. About 1/5 has a small amount of pleural effusion.

(2) Pathogen examination: The separation of Mycoplasma pneumoniae is difficult to be widely applied and does not contribute to early diagnosis.

(3) Serological examination: serum pathogen antibody titer>1:32, streptococcal MG agglutination test, titer 1:40 is positive, and the increase of more than 4 times in two consecutive times has diagnostic value. Indirect serum test >1:32, indirect fluorescence test >1:66, indirect immunofluorescence against Mycoplasma pneumoniae IgG>1:16, anti-Pneumococcal Mycoplasma IgM>1:8, avidin enzyme-linked immunosorbent assay, direct detection of pneumonia Mycoplasma antigen can be obtained within 24 hours and has diagnostic significance.

Differential diagnosis

1. Viral pneumonia: Respiratory syncytial virus, parainfluenza virus and adenovirus-induced pneumonia are common in children under 5 years old, and influenza virus pneumonia can be seen in influenza patients.

2. Bacterial pneumonia: pneumococcal pneumonia, rapid onset, often caused by cold, rain, upper respiratory tract infection and other incentives, there are chills, high fever, chest pain, rust sputum, lung consolidation signs, blood, visible white blood cells significantly increased, Isolation of pathogens from sputum and blood can be positive.

3. Parrot fever: There is a history of contact with birds (parrots, pigeons) or poultry, acute onset, fever, relatively slow pulse, headache, chills, confirmed by serological examination.

4. Rickettsia: mainly with Q fever, because Q heat sometimes takes pneumonia as the main performance, Q fever patients have contact or diet history with cattle, sheep, goats and their dairy products, serum complement binding test and ricketts The body agglutination test can confirm the diagnosis.

5. Fungal infections: Candida, Cryptococcus, Mucor, Histoplasma, Bud, etc., can be taken, urine for culture and smear; serum complement binding test, agar diffusion method, etc., if positive results are detected, Can be identified.

6. Tuberculosis: The onset of tuberculosis is slow, the course of disease is longer, and tubercle bacilli can be found in the sputum.

7. Others: Actinomycosis, nocardiosis, pulmonary infarction, atelectasis, bronchial lung cancer, pneumoconiosis and central nervous system diseases should also pay attention to differential diagnosis.

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