Pediatric chlamydial pneumonia

　　1. Etiology

　　Chlamydiae are divided into four species: Trachoma Chlamydia (Chlamydia trachomatis, CT), Pneumonia Chlamydia (Chlamydia pneumoniae, CPN), Psittacosis Chlamydia (Chlamydia psittaci, CP), and Swine Chlamydia (Chlamydia pecorum). Chlamydiae are bacteria but also have viral characteristics, with bacteria-like features such as a cell wall, similar reproductive and splitting methods, and DNA and RNA; and virus-like features such as growth only within cells. Common chlamydiae that cause pneumonia include CT and CP. Trachoma Chlamydia infection is one of the most common sexually transmitted diseases in developed countries and can also cause non-gonococcal urethritis or cervicitis, pelvic inflammatory disease. Vertical transmission from infected mothers can lead to conjunctivitis or Chlamydia trachomatis pneumonia in infants. Reports from abroad indicate that 1/4 of infants hospitalized for lower respiratory tract infections under 6 months of age are infected with CT, and Chinese research confirms that CT pneumonia accounts for 18.4% of infant pneumonia, becoming an important pathogen of infant pneumonia. Pneumonia Chlamydia is a newly named chlamydia species in 1989, and its infection is very common in the population. It can cause bronchitis and pneumonia and is now recognized as one of the important pneumonia pathogens in children and adults over 5 years old. In recent years, it has also been found to cause pneumonia in infants under 5 years old. Psittacosis Chlamydia pneumonia is a zoonotic disease. Humans become infected mainly by inhaling bird droppings, dust containing Psittacosis Chlamydia, or by contacting sick birds, which generally causes pneumonia, and a few cases can involve the central nervous system.

　　二、发病机制

　　衣原体过去曾归属立克次体，现分出成为独立一属。衣原体寄生于宿主细胞内，但不同于病毒，它具有细胞壁，含有DNA和RNA。CT是6个月以下小婴儿肺炎的主要病原之一，多由受感染的母亲通过产道分娩而传染。肺炎衣原体是20世纪80年代中期发现的一种新的衣原体生物种，是严格的人类病原体，不存在动物中间宿主，主要引起人类急性呼吸道感染，尤以肺炎多见，是5岁以上小儿及成人肺炎的病原之一。鹦鹉热衣原体主要寄生于鹦鹉及其禽类和低等哺乳动物体内，人通过与禽类接触或吸入鸟粪或被分泌物污染的羽毛而得病，罕见有人与人之间传播。肺炎衣原体主要通过呼吸道分泌物人与人之间传播，对人类呼吸道肺炎衣原体感染的发病机制及病理改变尚不十分清楚。沙眼衣原体的感染途径：

　　1、胎儿通过母亲产道时直接感染。

　　2、眼部感染衣原体后通过鼻泪管侵入呼吸道。鹦鹉热衣原体侵入呼吸道后经血侵入肝、脾等网状内皮细胞。在单核、吞噬细胞内繁殖后，由血行播散到肺及其他器官，在肺内引起小叶性或间质性肺炎、细支气管炎和支气管上皮细胞脱屑和坏死。病变部位可产生实变和少量出血，肺间质有淋巴细胞浸润，肺门淋巴结可肿大。肝脏可出现局部坏死，脾常肿大，心、肾、神经系统、消化系统等均可受累。

　　小儿衣原体肺炎只要及时发现和治疗有效，病儿可很快康复。但重症或孩子免疫力低下易出现下列并发症，如治疗不及时，则预后不良：

　　1. Emphysema:Shortness of breath, difficulty breathing, cough, sputum, fatigue, weight loss, decreased appetite, upper abdominal fullness, and other symptoms.

　　2. Atelectasis:Manifested by chest tightness, shortness of breath, difficulty breathing, dry cough, chest pain, sudden onset of difficulty breathing and cyanosis, cough, wheezing, hemoptysis, sputum, chills, fever, tachycardia, elevated body temperature, and decreased blood pressure, even shock.

　　3. Pulmonary bullae:Large pulmonary bullae can cause chest tightness and shortness of breath. Sudden enlargement and rupture of pulmonary bullae can produce spontaneous pneumothorax, causing severe difficulty in breathing, and can also cause chest pain similar to angina.

　　4. Bronchiectasis:Manifested by cough, sputum, chest tightness, and other symptoms.

　　5. Heart failure:The child is restless and anxious during the onset, with difficulty breathing and cyanosis, rapid breathing, >60 times/min, heart rate increases, >180 times/min, and there is liver enlargement, lower limb edema, and other symptoms. Immediate measures should be taken to control its development, using cardiotonics, diuretics, and other treatments.

　　6. Respiratory failure:The child is restless and anxious during the onset, with difficulty breathing and cyanosis, early breathing is accelerated, and the breathing rate slows down when the symptoms are severe. There are sighing breath and changes in breathing rhythm. In critical conditions, the heart rate may accelerate or slow down, and coma and convulsions may occur.

　　7. Ischemic hypoxic encephalopathy:When respiratory distress and hypoxia due to pneumonia are severe, children are prone to vomiting, headache, drowsiness, or restlessness, followed by coma and convulsions. The onset of encephalopathy is acute, with a fierce onset, serious condition, often with a variety of complications, intersecting with each other, affecting each other, making the condition more complex, and the mortality rate is high.

　　8. Shock:Sudden rise in body temperature to 40-41℃ or sudden drop, chills, pale and gray complexion, irritability or coma, sweating, skin changes like marble, blood pressure drop or undetectable, and at the same time, multiple organ dysfunction changes, symptoms are severe.

　　9. Intestinal paralysis:Manifested as severe abdominal distension, vomiting, constipation, and anal straining. Severe abdominal distension can compress the heart and lungs, making breathing more difficult. At this time, the child's face becomes pale and gray, the abdomen is tympanic on percussion, bowel sounds disappear, and the vomit may be coffee-colored or fecal-like. X-ray examination shows dilated intestines, thinning of the intestinal wall, elevation of the diaphragm, and the appearance of air-fluid levels in the intestinal cavity.

　　The onset is insidious, generally without fever, only mild respiratory symptoms such as runny nose, nasal congestion, and cough. Cough may persist and gradually worsen, with whooping cough-like paroxysmal cough, but without resonance. Accelerated breathing is a typical symptom, with occasional apnea or expiratory wheezing sounds, and two lung moist rales or wheezing sounds can be heard. Occasionally, pleural effusion may occur, and half of the patients may have abnormal conjunctivitis and tympanic membrane appearance. The peripheral blood picture often shows an increase in eosinophils. IgM, IgG, and IgA in the blood all increase. PaO2 decreases but PaCO2 is normal. Lung biopsy shows necrotizing bronchiolitis and pulmonary consolidation. The course is protracted, often lasting for several weeks, and most can recover spontaneously.

　　1. Medical history

　　Chlamydophila pneumoniae pneumonia often has a history of maternal infection and conjunctivitis, and is more common in infants. Psittacosis pneumonia often has a history of exposure to pathogens and their contaminants. Chlamydophila pneumoniae pneumonia is more common in older children, and most have no history of contact with sick birds.

　　Second, clinical manifestations

　　1. Trachoma chlamydial pneumonia: More common in infants within 3 months of age, especially around 3 weeks after birth. Generally, there are initial symptoms of upper respiratory tract infection such as runny nose and nasal congestion, and most do not have fever or low fever. Subsequently, coughing occurs, with whooping cough-like paroxysmal cough, but without sputum, increased respiratory rate is the typical symptom, and occasional apnea may occur. The lungs may produce moist rales, and sometimes expiratory wheezing sounds may be heard. It may be accompanied by myocarditis, pleurisy, pleural effusion, 50% with inclusion conjunctivitis and abnormal tympanic membrane appearance. The course of the disease is protracted, often lasting for several weeks.

　　2. Chlamydophila pneumoniae pneumonia: More common in older children, with a slower onset. Initially, there are symptoms of upper respiratory tract infection, often accompanied by sore throat, hoarseness, and fever. Subsequently, coughing becomes more severe and lasts longer, often lasting more than 3 weeks, and a few may be accompanied by myalgia, chest pain, and other symptoms. Pulmonary signs are often not obvious, and dry and moist rales can be heard. It is often accompanied by lymphadenopathy, and can also be complicated by otitis media, sinusitis, and Streptococcus pneumoniae infection. In recent years, it has been found that Chlamydophila pneumoniae can cause respiratory diseases, but can also cause diseases outside the respiratory system, such as myocarditis, encephalitis, and others.

　　3. Psittacosis chlamydial pneumonia: More common in older children and adults. The onset is often insidious, and mild cases may present with transient influenza-like symptoms. It can also start acutely with chills, headache, sore throat, fatigue, fever, with body temperature up to 40°C, relative bradycardia, severe cough, coughing up small amounts of sputum or blood, and can also appear nausea, vomiting, abdominal pain, and other gastrointestinal symptoms. Children may have symptoms such as drowsiness, delirium, convulsions, and other nervous and mental symptoms. The lungs often have no obvious signs, occasionally there may be moist rales, and in severe cases, there may be signs of lung consolidation. In addition, there may be endocarditis, anemia, reactive hepatitis, splenomegaly, proteinuria, nodular erythema, DIC, and other conditions.

　　Infants and young children should try to avoid contact with patients with respiratory tract infections as much as possible. It is recommended that children with respiratory tract infections should not go out, visit fewer places, and not go to public places. When parents have mycoplasma infection, they should try to minimize contact with young children and wear a mask when in contact; children with illness should be diagnosed and treated early, and erythromycin or azithromycin and other drugs should be used for treatment as soon as diagnosed; after the pneumonia is cured, do not be complacent, pay attention to strengthen nutrition, and improve the child's immunity.

　　1. Pathogenic examination:The smear of nasopharyngeal swabs stained with Giemsa can show the inclusion bodies of the pathogen stained with iodine in the cytoplasm. The sensitivity for diagnosis is only about 35%; cell culture for pathogen isolation is considered the gold standard at present, with a diagnostic sensitivity of 70% to 80% and specificity above 90%..

　　2. Serological examination:The微量immunofluorescence method detects CT or CPN in a single serum, with specific IgMCT-IgM ≥ 1:64, CPN-IgM ≥ 1:16 or CPN-IgG ≥ 1:512, or a fourfold increase in antibody titer in paired serum examinations, indicating acute infection. If IgG ≥ 1:16 but.

　　3. PCR detection:The specific DNA PCR method is fast, simple, sensitive, and specific.

　　4, CT pneumonia:Diffuse interstitial lesions and patchy lung infiltration with emphysema can be seen.

　　5, CPN pneumonia:It is mostly unilateral segmental infiltration, with the lower lobe and surrounding areas more common, and a few cases may have bilateral lesions. Severe cases may be accompanied by pleural effusion. Pulmonary signs and X-ray findings often take more than a month to disappear. Psittacosis chlamydial pneumonia is characterized by infiltrative foci radiating from the hilum, often involving the lower lobes of both lungs, presenting as diffuse interstitial pneumonia or bronchopneumonia, occasionally showing granuloma-like nodules or consolidation foci, or signs of pleural effusion.

　　In the bodies of patients with pneumonia, there is often a disorder of water, electrolytes, and acid-base balance, so it is advisable to eat foods rich in iron, such as animal livers and yolks; foods high in copper, such as beef liver, sesame sauce, pork, etc.; and also shrimp shells, dairy products, and other high-calcium foods. It is best to eat less cold and cool fruits, as they can damage the Yang of the spleen and stomach, hinder the function of transformation and transportation, and are not conducive to the recovery of the disease. In the diet of pneumonia patients, fruits should be eaten in moderation and selected for variety.

　　I. Treatment

　　Macrolide antibiotics are the first choice. Use erythromycin 40mg/(kg/d) or roxithromycin, azithromycin 10mg/kg each time, once a day, orally, for 3 days, then stop for 4 days, as a course of treatment. Clarithromycin and others, taken orally continuously for about 2-3 weeks, can shorten the course of the disease. In cases where oral administration is not possible or in severe cases, erythromycin is administered intravenously, 15mg/kg each time, twice a day; or roxithromycin 4mg/kg, clarithromycin 10mg/kg, twice a day, orally; penicillins and aminoglycosides are ineffective. The prognosis of the disease is good, but there are reports that some children still have respiratory symptoms such as cough, asthma, and abnormal lung function after 7-8 years of follow-up after recovery.

　　II. Prognosis

　　The course of the disease is prolonged, lasting for several weeks, but most can be cured.鹦鹉热衣原体肺炎重症病死率高，但近年来应用有效抗生素治疗后，病死率明显下降。有作者经血清学调查发现肺炎衣原体感染与冠状动脉粥样硬化性心脏病之间有关联，亦有人发现肺炎衣原体感染可引起哮喘或哮喘性支气管炎，值得研究。