Overview.
Influenza virus pneumonia is an infectious disease of the lungs caused by the influenza virus invading the lower respiratory tract. It can be caused by direct invasion of the virus itself or by secondary bacterial infection. Influenza virus pneumonia tends to occur in patients with underlying lung and heart disease, pregnant women, infants, young children, the elderly, or the immunodeficient. It presents early with influenza symptoms, and those with rapid progression of the disease have a higher mortality rate.
Causes
Influenza virus belongs to the family of Orthomyxoviridae, which is an RNA virus, spherical or elongated, with a diameter of 80 to 120 nm. its internal dense core is composed of 8 segments of single-stranded RNA and protein composed of nucleoprotein, and its outer membrane surface has hemagglutinin and neuraminidase glycoprotein protrusions. Hemagglutinin is the major surface antigen of influenza virus, and antibodies against hemagglutinin neutralize the virus and play a major role in anti-influenza virus immunity. Antibodies against neuraminidase limit the release of influenza virus and reduce the incidence of infection. Influenza viruses are usually divided into 3 types, A, B, and C, based on the specificity of the nucleoprotein. Type A viruses are prone to gene fragment rearrangement resulting in antigenic replacement, and are prone to periodic antigenic variation, producing new subspecies and variants and causing worldwide pandemics; type B viruses are mostly only genetically fragmented point mutations, causing antigenic drift, and are often the cause of localized outbreaks and epidemics because of small antigenic variation and the formation of variants only; type C viruses have no antigenic variation and are only found in a scattered form.
Symptoms
The onset of the disease often begins with general influenza symptoms, such as acute onset, cough, sore throat, accompanied by fever, headache, myalgia discomfort, symptoms continue unabated, followed by high fever, shortness of breath, cyanosis, paroxysmal cough, most of the more intense, sputum is often very little, but may be sputum with blood. Secondary bacterial infection often occurs within 2 weeks of the onset of the disease, manifested by high fever or symptoms once reduced and then worsened. The sputum becomes purulent, and the signs and symptoms of bacterial pneumonia appear. The pathogens are mostly Streptococcus pneumoniae, Staphylococcus aureus and Haemophilus influenzae. It is common in people with chronic heart and lung diseases, chronic metabolic diseases, and chronic kidney disease, leading to the deterioration of the underlying disease. On physical examination, the respiratory sounds of both lungs are low, and dry and wet rales can be heard in the corresponding parts of the lesion, but there are no solid signs.
Examination
1. Laboratory examination
The white blood cell count is highly variable, and may be normal or low in the early stages, and then may be mildly increased, and the proportion of lymphocytes is often increased. In significant viral or bacterial infections, severe leukopenia may occur. When the white blood cell count exceeds 15×109/L, it often suggests the presence of secondary bacterial infection.
2. Pathogenetic examination
Smear test for influenza virus antigen, PCR technique for viral gene detection and culture for virus isolation.
3. X-ray examination
In the early stage of the disease, inflammatory infiltration can be seen along the lung gate towards the periphery, with the progression of the disease, there may be scattered flaky or flocculent shadows, which are often distributed in multiple lung fields, and in the late stage, there are fusion changes, which are concentrated in the inner and middle zones of the lung fields, similar to pulmonary edema.
4. Other
Including hemagglutination inhibition test, complement binding test. Using the current domestic representative strain or the local newly isolated virus strain to test the acute and recovery serum, the antibody elevation of more than 4 times has the diagnostic value. Diagnosis of secondary bacterial pneumonia can be confirmed by bacterial culture of sputum, lung tissue, pleural effusion blood and other specimens.
Diagnosis
The diagnosis of influenza virus pneumonia depends on the onset of influenza epidemic and typical clinical manifestations, the isolation of influenza virus in sputum and other secretions as well as lung tissues, and the exclusion of bacterial and other pathogenic infections such as epidemic encephalitis, legionnaires’ disease, mycoplasma pneumonia, etc.; the confirmation of the diagnosis relies on the pathogenetic examination.
Treatment
1. The treatment of influenza virus pneumonia focuses on maintaining the patient’s organ function, especially the oxygenation of the lungs, and providing timely respiratory and hemodynamic support.
2. Antiviral drugs are only used for the early prevention and treatment of influenza A virus, therefore, such drugs can only prevent the influenza virus from entering the cells, but are ineffective against the virus that has already entered the cells, therefore, it is necessary to apply them at an early stage in order to reduce the symptoms and shorten the duration of the disease.
3. Early use of sensitive antimicrobial drugs is recommended in combination with bacterial infections. If the disease is serious or combined with underlying diseases, it is advisable to use broad-spectrum antibiotics at an early stage in order to save the patient’s life.
4. For those with high temperature and severe symptoms of poisoning, nutritional support should be given to maintain the stability of the internal environment, physical hypothermia, and other treatments include bed rest, drinking more water, preventing and controlling secondary bacterial infections, and symptomatic treatments such as relieving cough and resolving phlegm.
5. Appropriate traditional Chinese medicine treatment is conducive to anti-virus, enhancement of patients’ immunity and cooling.
Prevention
Patients should be isolated to prevent cross-infection. Application of live attenuated and inactivated vaccine has certain preventive effect. Since the strains of each influenza epidemic often mutate, it is best to keep the vaccine strains as close as possible to those of the epidemic period. For people with underlying diseases or the elderly and frail, they should minimize going out during the influenza season, avoid crowded environments, and get vaccinated against influenza and pneumonia.