Influenza virus pneumonia

　　Influenza viruses are mainly transmitted through airborne droplets, with patients being the primary source of infection. The virus is present in mucus, sputum, and saliva, and is expelled from the body through coughing and sneezing. The influenza virus (influenza virus) belongs to the family Orthomyxoviridae and is an RNA virus, appearing spherical or elongated with a diameter of 80-120 nm. Its dense core is composed of a single-stranded RNA and protein nucleoprotein consisting of 8 segments, and its outer membrane surface has glycoprotein protrusions composed of hemagglutinin and neuraminidase. Hemagglutinin is the main surface antigen of the influenza virus, and antibodies against hemagglutinin can neutralize the virus, playing a major role in antiviral immunity. Antibodies against neuraminidase can limit the release of influenza viruses, reducing the occurrence of infection. Influenza viruses are usually divided into three types (A, B, and C) based on the specificity of the nucleoprotein. Influenza A viruses are prone to gene segment rearrangement, resulting in antigenic shift and easy occurrence of antigenic variation, producing new subtypes and variants, causing worldwide pandemics; influenza B viruses often only undergo gene segment point mutations, causing antigenic drift, due to smaller antigenic variation, only forming variants, so they often cause local outbreaks and small epidemics; influenza C has no antigenic variation and only appears in scattered form. There were five worldwide influenza pandemics in the mid-19th century, and the epidemic in 1918 caused the death of 20 million people. In China, from the 1950s to the early 1980s, there were more than ten outbreaks of influenza A virus, and in the mid-1980s, influenza outbreaks were mainly sporadic and small, without obvious epidemics. Since the 1990s, there have been several outbreaks of influenza B in northern China.

　　Influenza virus pneumonia can lead to secondary bacterial pneumonia. Symptoms of upper respiratory tract infection and intoxication, such as sore throat, nasal congestion, runny nose, fever, headache, and general malaise, rapidly worsen after 24 hours of onset. High fever, irritability, severe cough, bloody sputum, and dyspnea and cyanosis occur. The respiratory sounds in both lungs are low, and dry and wet rales are遍布, but there are no signs of lung consolidation.

　　Influenza virus pneumonia is more common in the young, pregnant women, and the elderly over 65 years old, especially in those with increased left atrial pressure, such as mitral stenosis, but it can also occur in normal people, being a direct and severe pulmonary viral infection. The onset is often accompanied by general influenza symptoms, such as a sudden onset, cough, sore throat, accompanied by fever, headache, myalgia, and discomfort. Symptoms continue to progress, with high fever that does not subside, dyspnea, cyanosis, paroxysmal cough, and hemoptysis. The amount of sputum is usually small, but it can be bloody. Secondary bacterial infection often occurs within 2 weeks of onset,表现为 fever or symptoms initially improved and then worsened. Sputum turns into purulent, and symptoms and signs of bacterial pneumonia appear. The pathogens are usually Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and others. Common in patients with chronic heart, lung diseases, chronic metabolic diseases, and chronic kidney disease, leading to deterioration of the underlying disease. Physical examination shows low respiratory sounds in both lungs, and dry and wet rales can be heard in the corresponding lesions, but there are no signs of consolidation.

　　Patients should be isolated and prevent cross-infection. The use of attenuated live vaccine and inactivated vaccine has a certain preventive effect, as the virus strains in each influenza epidemic often vary, and the vaccine strain is best to be as close as possible to the strain in the epidemic period. Amantadine and rimantadine have a certain preventive effect against type A influenza, and early application can reduce the incidence of influenza virus pneumonia, but they are ineffective against type B influenza, so the strain type needs to be determined in the early stage of the epidemic. Chinese herbal medicine for prevention can also be tried.

　　Pneumonia caused by influenza virus diagnosis depends on the onset during the influenza epidemic period and typical clinical manifestations, sputum and other secretions, and influenza virus isolated from lung tissue. Influenza virus can be cultured in tissue cells or yolk sacs, isolated from respiratory secretions and lung tissue, usually requiring 48-72 hours. Viral antigens can be detected in early tissue culture or nasopharyngeal lavage fluid by immunofluorescence technology and enzyme-linked immunosorbent assay, which are rapid and highly sensitive, and have early diagnostic value. Other detection methods include hemagglutination inhibition test, complement fixation test, detection of acute and convalescent serum antibodies with the current Chinese representative strain or locally newly isolated virus strain, and a rise of more than 4 times has diagnostic value. The diagnosis of secondary bacterial pneumonia can be confirmed by bacterial culture of sputum, lung tissue, pleural effusion, blood, and other specimens.

　　Other laboratory tests are not helpful for the specific diagnosis of influenza virus pneumonia, with a wide range of changes in blood leukocyte count, which is often low in the early stage and can become normal or slightly increased later; in significant viral or bacterial infections, severe leukopenia may occur; when the leukocyte count exceeds 15×10⁹L(15000/μl) often suggests the presence of secondary bacterial infection.

　　A chest X-ray examination shows inflammatory infiltration along the hilum to the periphery in the early stage, followed by scattered patchy or fluffy shadows, commonly distributed in multiple lung fields; in the late stage, it presents with融合 changes, mostly concentrated in the middle and inner zones of the lung fields, similar to pulmonary edema.

　　During the treatment of influenza virus pneumonia, patients should follow a light diet, pay attention to reasonable dietary matching, provide a diet rich in protein and diverse in vitamins, eat more fresh vegetables and fruits, and pay attention to dietary hygiene.

　　The treatment of influenza virus pneumonia mainly focuses on maintaining pulmonary oxygenation function and providing timely respiratory and hemodynamic support. Antiviral drugs such as rimantadine and amantadine are only used for the early prevention and treatment of influenza A virus, as these drugs only prevent the influenza virus from entering cells and are ineffective against the virus that has already entered the cell. Therefore, early application is necessary to alleviate symptoms and shorten the course of the disease. There is no definite opinion on whether rimantadine can improve survival and shorten the course of influenza virus pneumonia, but clinical medical experts still recommend its use. Rimantadine is administered at a dose of 100-200mg daily, divided into two doses, for a course of 5-7 days. Due to its renal excretion and the possibility of causing excitement, dizziness, ataxia, and other side effects, caution should be exercised in patients with renal insufficiency, central nervous system diseases, and those over 65 years old. The application of neuraminidase inhibitors can be referred to in the treatment of influenza. It is advisable to use appropriate antibacterial drugs as early as possible in cases of concomitant bacterial infection. Patients with severe fever and poisoning symptoms should be given intravenous fluid therapy and physical降温. Other treatments include bed rest, adequate fluid intake, prevention and treatment of secondary bacterial infections, and symptomatic treatment such as cough suppression and expectoration.

　　Except for newborns of 5 months old, all ages, genders, and professions are susceptible to infection. Those with pre-existing chronic cardiorespiratory diseases and the elderly are considered high-risk populations.