Pediatric influenza virus pneumonia

　　1、发病原因：流感病毒分为甲、乙、丙三型，具有血凝素(HA)及神经氨酸酶(NA)二种表面抗原，易发生抗原变异。目前流行的型别(1977年以来)有新甲1型(H1N1)及甲3型(H3N2)同时存在，少数为乙型。

　　2、发病机制：流感病毒经飞沫传播侵入患者的上、下呼吸道或直接进入肺泡，停留在呼吸道上皮细胞黏液薄膜中的流感病毒，能和宿主细胞的黏蛋白等特异性受体相结合，局部黏液分泌物中的抗体(主要是IgA)能与病毒结合而中和。黏液中尚有糖蛋白抑制素，能与病毒结合，阻止病毒附着在宿主细胞的特异性受体上，以达到防止感染的目的，但这些抑制物最终被病毒本身的神经氨酸酶所破坏，结果使病毒得以进入呼吸道上皮细胞，并在其中进行繁殖。在这些细胞中新合成的病毒颗粒，能穿过呼吸道黏液而进入其他细胞或血液中。引起进行性感染，从而出现一系列的临床症状。气管、支气管和细支气管及肺泡管上皮细胞，受流感病毒的侵袭后发生变性、坏死及出血灶，同时有淋巴细胞、浆细胞浸润，结果使黏膜肿胀，细胞脱落而致管腔狭窄，使气体通过发生障碍，尤以呼气时最明显，从而引起肺气肿。若阻塞的细支气管内气体被吸收，则可发生肺不张。肺泡腔内充满含中性粒细胞、单核细胞和红细胞的炎性分泌物，严重影响气体交换，从而导致不同程度的缺O2状态。若继续进展，则PO2下降，CO2潴留，加之流感病毒毒素作用和代谢异常及酸碱平衡紊乱等因素，可造成高热、昏迷、惊厥和呼吸循环衰竭等中毒症状。用荧光抗体染色证明支气管、细支气管、肺泡的表皮细胞和肺泡中的巨噬细胞存在着病毒感染灶，而血管内皮细胞中则无。病毒引起呼吸道表皮细胞病变，使其抵抗力降低，给继发性细菌感染创造了条件。由于流感病毒感染肺部，使其充血、水肿，气管、支气管与细支气管黏膜充血，管内可见血性分泌物。镜检见纤毛上皮细胞坏死脱落，有的发生增生。黏膜下层灶状出血和水肿及细胞浸润。肺泡有纤维蛋白与渗出液，混有中性粒细胞和单核细胞，有的可见透明膜，肺泡间质增厚。

　　It can be complicated by pulmonary edema, pleural effusion; neurological damage can lead to toxic encephalopathy and brain edema; cardiovascular dysfunction can lead to shock, and myocarditis and pericarditis are more likely to occur; Reye syndrome is often complicated; and kidney lesions can occur, manifested as hematuria and proteinuria. Influenza pneumonia with concurrent bacterial infection is more common, with Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and hemolytic streptococcus being common pathogens. The lesions can be bronchopneumonia, lobar pneumonia, or lung abscess. Most cases present with simple influenza virus pneumonia, with improved condition, fever recurrence after defervescence, increased systemic toxicity, elevated body temperature, exacerbated cough, dyspnea, marked cyanosis, widespread wet sounds on chest auscultation, and dullness on percussion. Blood count shows significant increase in white blood cells and neutrophils, and occasionally encephalitis, DIC, and other diseases may occur.

　　Based on the cases observed in Beijing and Tianjin in 1953, the submucosal influenza virus (H1N1) was isolated. The following are the clinical key points:

　　1. Acute onset:Most patients have persistent high fever for 48 hours after onset, and a few patients may gradually rise after a moderate fever for 2 to 3 days.

　　2. Respiratory system symptoms and signs:Respiratory symptoms are significant, with severe wheezing, sometimes still wheezing after fever subsides. Lung signs such as dullness on percussion, changes in respiratory sounds, and fine moist rales or crackles all gradually occur after onset. Pleural effusion can be seen, mostly yellowish slightly cloudy fluid, ranging from tens to hundreds of milliliters. In a few cases, pharyngeal redness and pseudomembrane formation have been observed, which are easily peeled off.

　　3. Digestive system:Vomiting and diarrhea are common, and vomiting can be severe, sometimes even vomiting coffee-like substances; diarrhea may occur simultaneously with pneumonia, or it may occur concurrently with the improvement of respiratory symptoms. In some severe cases, intestinal hemorrhage may occur, leading to a poor prognosis.

　　4. Nervous system:Occasionally, neurological symptoms are significant, even early persistent coma, or convulsions occur. Cerebrospinal fluid examination shows normal findings except for slightly increased pressure.

　　5. Laboratory examination:Leukopenia, with an increased percentage of lymphocytes.

　　6. X-ray examination:In most cases, irregular fluffy or small spherical shadows can be seen in the lung fields on both sides of the hilum, which is not extensive; in a few cases, large shadow can occur. During the flu epidemic, many infants and young children may simultaneously develop the disease within a short period of time, with persistent high fever, and symptoms and signs of pneumonia. When antibiotic treatment is ineffective, the diagnosis of influenza pneumonia should be considered. Confirmation of the diagnosis requires virological examination, including viral isolation from nasopharyngeal secretions or throat swabs, as well as the double-antibody hemagglutination inhibition test or complement fixation test. However, it is still difficult to popularize in general hospitals. In recent years, monoclonal antibody indirect immunofluorescence method has been used for rapid viral diagnosis, and a positive result has diagnostic significance.

　　For the prevention of influenza virus pneumonia, it is necessary to first prevent influenza, that is, to frequently grasp the dynamic changes of foreign epidemic situations and virus mutations, and the immune status of the population. It is conducive to epidemic investigation, so as to take preventive measures in time. Strengthen health education and publicity, strive to achieve the five early goals, namely early detection, early diagnosis, early reporting, early isolation, and early treatment. At the same time, try to reduce the opportunities for transmission. During the influenza epidemic period, avoid entering crowded places. Secretions and contaminants from the patient's nasopharynx should be disinfected at any time. Some people have used vaccines for preventive injection, and most of the vaccines are inactivated vaccines with type A as the main component. However, influenza viruses constantly mutate, so it is necessary to select the attenuated strain to prepare vaccines in a timely manner. The vaccination method of inactivated influenza vaccine is a subcutaneous injection once, followed by a re-injection after an interval of 6 to 8 weeks. Generally, it is carried out in September and October, and a booster immunization injection is given every autumn thereafter. There are three types of monovalent inactivated influenza vaccines produced in China, namely chick embryo urine live vaccine, whole embryo live vaccine, and tissue culture live vaccine. The vaccination method is nasal spray, and it is better to be vaccinated 1 to 2 months before the epidemic. After vaccination, there may be slight respiratory symptoms, and some may have fever. The effective protection time is 6 months to 1 year. Generally, infants, children, the elderly, and the weak are not recommended to be vaccinated. As for drug preventive methods, amantadine hydrochloride, because it can prevent influenza viruses from entering human cells, has a certain preventive effect, but it is ineffective against type B. The oral dose for adults is 100mg, twice a day, and the dose for children should be reduced accordingly, taking for 7 to 10 days. The toxic reaction is excitement, dizziness, and ataxia. The Ningbo and Hangzhou health and epidemic prevention stations reported that morinamide (virucide) has a significant effect on type A2 influenza. In terms of preventing influenza with traditional Chinese medicine, various single and compound herbal formulas can be tried, and many experiences have been gained, which is worthy of further research and observation.

　　1. Blood count:Leukopenia, which can be as low as (1-2)×10^9/L, with an increased percentage of lymphocytes. Some cases of influenza pneumonia may not have secondary bacterial infection, but the total leukocyte count and neutrophils can also increase, with left shift of the nucleus. When there is concurrent bacterial infection, the blood leukocyte and neutrophil counts are significantly increased.

　　2. Cerebrospinal fluid examination:Cerebrospinal fluid examination shows little change except for increased pressure, and sometimes there is a slight increase in protein.

　　3. Urinalysis:Kidney lesions may cause hematuria and proteinuria.

　　4. Blood biochemistry:Erythrocyte sedimentation rate is normal or increased, and blood ammonia levels rise, etc.

　　5. Virus isolation and serological examination:Collect secretions from the child's throat during the acute phase, best within 3 days, as the isolation positivity rate gradually decreases after 3 days. Foreign reports show that nasopharyngeal lavage has a higher positivity rate than throat swabs. The specimens should be inoculated into the amniotic cavity of 10-12 day-old chick embryos, or into primary human embryo kidney or monkey kidney cells, but the latter is less sensitive than the former. Double-serum antibody assays should be performed on acute and convalescent sera, and hemagglutination inhibition tests and complement fixation tests should be performed. A positive result is defined as convalescent serum antibodies greater than or equal to 4 times the acute phase, which appear earlier than hemagglutination by 16 hours and earlier than cytopathic effects by 48 hours. The difference between immunoenzyme staining and immunofluorescence methods is the marker used, and enzyme-labeled antibodies are used for detection. A positive result is indicated by the appearance of nuclei and/or cytoplasm stained brownish on the cell smear.

　　6. X-ray examination:Irregular fluffy or spherical shadows can be seen on both sides of the hilum in most cases, not widespread; in a few cases, large shadowing can occur.

　　7. Electrocardiogram:Abnormal electrocardiogram findings when myocardial damage occurs.

　　8. Ultrasound:Liver enlargement.

　　The diet for children with influenza virus pneumonia should be light and nutritious, with a focus on foods rich in vitamins, such as fruits, apples, peaches, bananas, pears, cherries, oranges, and more lean meat to strengthen the body. Try to eat less spicy and stimulating foods. For example: onions, pepper, chili, Sichuan pepper, mustard greens, fennel. Caffeinated beverages. Avoid second-hand smoke.

　　1. Treatment

　　There are few foreign reports on the treatment of influenza virus pneumonia with amantadine, mainly because the medication is too late after the onset of pneumonia. Ribavirin (triazine nucleoside) has also not been reported for the treatment of childhood influenza virus pneumonia abroad, and it can be tried with aerosol or intravenous injection. Other treatments can be referred to in viral pneumonia.

　　2. Prognosis

　　Primary influenza virus pneumonia is relatively serious, and the fever course can last for about 10 days, but since 1963, most Chinese cases have a good prognosis and almost no deaths. Recently, foreign reports show that long-term sequelae of severe influenza virus pneumonia can include atelectasis, bronchiectasis, and pulmonary fibrosis, etc.