Influenza (hereinafter referred to as influenza ) is an acute respiratory infectious disease caused by influenza virus . Influenza A and B viruses are seasonal every year, among which influenza A virus can cause a global pandemic. The national influenza monitoring results show that in October every year, all parts of my country have entered the winter and spring epidemic season.
Influenza is onset and although most of them are self-limiting, some patients have become severe cases due to complications such as pneumonia and or worsening underlying diseases. A few cases have rapid progress and may die due to complications such as acute respiratory distress syndrome (ARDS), acute necrotizing encephalopathy or multi-organ insufficiency.
1 Pathogenic
influenza virus belongs to the family Orthomyxviral family, and is a single strand, negative chain, and segmented RNA virus. According to the difference between nucleoprotein and matrix protein, it is divided into four types: A, B, C and D.
Currently, infected with humans is mainly H1N1, H3N2 subtypes in influenza A virus and Victoria and Yamagata lines in influenza B virus. influenza virus is sensitive to commonly used disinfectants such as ethanol , iodine, and iodine tincture; it is sensitive to ultraviolet rays and heat, and can be inactivated at 56℃ for 30 minutes.
2 Epidemiology
2.1 Infection source Patients and recessively infected people are the main sources of infection. It is contagious from the end of the incubation period to the acute period. The virus generally continues to detoxify 3 to 7d in human respiratory secretions. The virus detoxification time for children, immune function impaired and critically ill patients can exceed 1 week.
2.2 pathway virus mainly spreads through sneezing and coughing and other droplets, and is directly or indirectly infected through the mucosa such as the mouth, nose, eyes, etc. Contact with article , which is contaminated by the virus, can also be infected through the above channels. It can also be propagated in the form of aerosol (diameter 100 μm). Moreover, the smaller the diameter of the aerosol, the further the propagation distance.
2.3 The susceptible population is generally susceptible to .
2.4 High-risk populations of severe cases should undergo influenza virus nucleic acid testing and other necessary examinations as soon as possible, and provide antiviral drugs for treatment.
(1) Children aged ＜5 years old (age ＜2 years old is more likely to have serious complications);
(2) elderly people aged ≥65 years old;
(3) those with the following diseases or conditions: chronic respiratory diseases, cardiovascular diseases (except hypertension ), kidney disease, liver disease, hematological system diseases, nervous system and neuromuscular diseases, metabolic and endocrine system diseases, malignant tumors, immune function suppression, etc.;
(4) Obese people [BMI) > 30];
(5) Pregnant and perinatal women.
3 Pathogenesis and pathological changes
3.1 Pathogenesis Influenza A and B viruses initiate infection by binding to sialic acid receptors on the surface of of respiratory tract epithelial cells. influenza virus enters host cells through endocytosis, and the viral genome is transcribed and replicated in the nucleus, replicating a large number of new progeny viruses and infecting other cells. After the influenza virus infects the human body, in severe cases, it can induce cytokine storm , leading to infection and poisoning.
3.2 Pathological changes are mainly manifested in the clustered shedding of epithelial cells in respiratory tract, metaplasia of epithelial cells, congestion of lamina propria mucosal cells, edema of with monocyte infiltration and other pathological changes . Severe cases may change in pneumonia; critically ill patients may be accompanied by diffuse alveolar damage; diffuse congestion, edema, and necrosis of brain tissue occurs when combined with encephalopathy, acute necrotic encephalopathy is manifested as symmetric necrotic lesions mainly in thalamus ; interstitial bleeding, lymphocyte infiltration, cardiomyocyte swelling and necrosis occurs when combined with heart damage.
4 Clinical manifestations and laboratory examination
incubation period is generally 1 to 7 days, mostly 2 to 4 days.
4.1 Clinical manifestations It mainly occurs with fever, headache, myalgia and general discomfort. The body temperature can reach 39-40°C. It may be afraid of chills and chills, which are often accompanied by systemic symptoms such as joint pain in the body, fatigue in the , loss of appetite, and sore throat. It may be caused by nasal congestion, runny nose, poststernum discomfort, flushing face, congestion in the conjunctiva, etc. Some patients have mild or asymptomatic symptoms. Children usually have higher fever than adults, and gastrointestinal symptoms such as nausea, vomiting, and diarrhea during influenza B are also more common than those in adults. newborns can only show drowsiness, , milk refusal, apnea, etc. The course of the disease is self-limiting than the onset of the disease. The fever gradually subsides after 3 to 5 days, and the systemic symptoms improve, but cough and physical strength often take a long time to recover.
4.2 Complications
pneumonia is the most common complications, and other complications include nervous system damage, heart damage, myositis, rhabdomyolysis, shock, etc. Influenza in children, laryngitis , otitis media , bronchitis is more common than in adults.
4.2.1 Influenza virus can invade the lower respiratory tract, and causes primary viral pneumonia. Some patients with severe influenza may be infected with with bacteria, fungi and other pathogens, and in severe cases, ADRDS may occur.
4.2.2 Neurological damage includes meningitis, encephalitis , myelitis , encephalopathy, Guillain-Barre syndrome, etc. Among them, acute necrotizing encephalopathy is more common in children.
4.2.3 Heart damage mainly includes myocarditis and pericarditis . It can be seen that myocardial markers, electrocardiograms, heart ultrasound and other abnormalities can be seen. In severe cases, heart failure may occur. In addition, after influenza infection, the risk of hospitalization and death related to myocardial infarction, ischemic heart disease is significantly increased.
4.2.4 myositis and rhabdomyolysis are mainly manifested as myalgia, myasthenia , serum creatine kinase , and myoglobin increase. In severe cases, it can lead to acute kidney injury , etc.
4.3 Laboratory examination
4.3.1 Blood routine The total number of peripheral blood leukocytes is generally not high or decreases , and the lymphocyte count in severe cases is significantly reduced.
4.3.2 Blood biochemistry may include aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase , creatinine, etc. A few cases have increased creatine kinase; some cases have hypokalemia and other electrolyte disorders. Blood lactate can be elevated in shock cases.
4.3.3 Arterial blood gas analysis Severe patients may have aerobic partial pressure, blood oxygen saturation, and oxygenation index , and their acid and base imbalances.
4.3.4 Cerebrospinal fluid The number of cells and proteins of central nervous system affected subjects can be normal or increased; acute necrotic encephalopathy is typically manifested as approximately normal cell number and increased proteins.
4.3.5 Etiology-related examination
It is best to collect upper respiratory tract specimens of patients in within 4 days after the symptoms of appear. However, there are also reports that severe lower respiratory tract infection patients can also detect viruses in 1 week, and patients with low immune function may last for weeks or even months. The suggestions for collecting specimens are as follows: (1) nasopharyngeal specimens are better than other upper respiratory tract specimens, and the detection rate of influenza virus is higher; (2) If there is no nasopharyngeal specimens, nasal and pharyngeal swab specimens are combined better than these two separate tests; (3) Middle turbinate swabs are better than pharyngeal swabs; (4) Flocked swabs are better than non-flocked swabs.
4.3.5.1 Viral antigen detection Viral antigen detection can be done by colloidal gold method and immunofluorescence method. Antigen detection speed is fast, but the sensitivity is lower than nucleic acid detection. Viral antigen tests are positive to support diagnosis, but is negative to rule out influenza.
4.3.5.2 Viral nucleic acid detection The sensitivity and specificity of viral nucleic acid detection are very high, and can distinguish virus types and subtypes. Currently, it mainly includes real-time fluorescence quantification PCR and fast multiplex PCR. Fluorescence quantification PCR method can detect influenza virus nucleic acid in respiratory tract specimens (nasopharyngeal swabs, pharyngeal swabs, tracheal extracts, sputum). The best specimen is a nasopharyngeal swab, and can distinguish influenza virus subtypes.For severe patients, the detection of lower respiratory tract (sputum or tracheal extract) specimens is more accurate.
4.3.5.3 Virus culture isolation Influenza virus can be isolated from respiratory specimen culture.
4.3.5.4 Serological test The recovery period of IgG antibody levels was 4 times or more higher than that of the acute period, which was retrospectively diagnostic. Ｉｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅｒｅ� Only when the double serum antibody titer increases by 4 times or more can it be retrospectively diagnosed.
4.4 imaging manifestations In patients with primary viral pneumonia, imaging manifestations are patchy, ground-glass shadows, and multilobular exudate lesions in the lungs; those who progress rapidly can develop into diffuse exudate lesions or consolidation in both lungs, and pleural effusion can be seen in individual cases. Acute necrotizing encephalopathy CT or MRI can be seen symmetry and multifocal brain injury, including bilateral thalamus, perianal white matter, internal capsule, putamen, nucleus, brain stem, thigh cover (fourth ventricle, ventral side of midbrain water tube), and cerebellar medulla, etc.
5 Diagnosis
is mainly used to diagnose it in combination with epidemiological history, clinical manifestations and etiology examinations. During the flu epidemic season, even if the clinical manifestations are atypical, especially those with high-risk factors for severe influenza or hospitalized patients, the possibility of influenza is still necessary to consider and etiological testing should be performed. During the active influenza period, influenza is mainly diagnosed based on clinical manifestations (Table 1). Cough and fever are the most diagnostic clinical manifestations.
5.1 clinically diagnosed case has an epidemiological history (with close contact with suspected or confirmed influenza patients without effective personal protection 7 days before the onset of the disease, or one of the patients with influenza-like cases, or there is clear evidence of infectious infection with others) and other diseases that cause influenza-like symptoms are excluded.
5.2 confirmed that the diagnosed case
has the above clinical manifestations of influenza, and has one or more pathogenic test results positive:
(1) The nucleic acid test for influenza virus is positive.
(2) tested positive for influenza antigen.
(3) influenza virus culture isolation was positive.
(4) Influenza virus-specific IgG antibody levels in the acute and recovery periods were 4 times or more.
6 Severe and critical cases 6.1 One of the following conditions is Severe case
(1) Continuous high fever >3 days, accompanied by severe cough, coughing of pus and sputum, blood sputum, or chest pain ;
(2) Fast breathing frequency, dyspnea , cyanosis of the lips;
(3) Slow reaction, drowsiness, agitation and other mental changes or convulsions ;
(4) Severe vomiting and diarrhea, dehydration manifestations;
(5) Combined with pneumonia;
(6) The original underlying disease is significantly worsened;
(7) Other clinical situations that require hospitalization.
6.2 The following cases are critical cases
(1) respiratory failure ;
(2) acute necrotizing encephalopathy;
(3) shock;
(4) multi-organ insufficiency;
(5) other serious clinical situations that require monitoring and treatment.
7 Differential diagnosis
7.1 Common cold : The systemic symptoms of influenza are heavier than the common cold; tracking the epidemiological history helps to distinguish; the influenza etiology test for common cold is negative, or corresponding etiology evidence can be found.
7.2 Other upper respiratory tract infections : including acute pharyngitis , tonsillitis , rhinitis and sinusitis . Infections and symptoms are mainly limited to the corresponding parts. Influenza etiology test was negative.
7.3 Other lower respiratory tract infections: Influenza has symptoms of cough or if it is combined with tracheal bronchitis, it is necessary to distinguish it from acute tracheal bronchitis; when it is combined with pneumonia, it is necessary to distinguish it from pneumonia caused by other pathogens (other viruses, mycoplasma , Chlamydia , bacteria, fungi, Mycobacterium tuberculosis , etc.). Preliminary judgments can be made based on clinical characteristics, and etiology examinations can be used to confirm the diagnosis.
7.4 New Coronavirus Pneumonia: The mild or ordinary type of new coronavirus can manifest as symptoms such as fever, dry cough, sore throat, etc., which is not easy to distinguish from influenza; severe and critical types are severe pneumonia, ADRDS and multi-organ dysfunction, which is similar to the clinical manifestations of severe and critical influenza. It should be distinguished in combination with epidemiological history and etiology.
