Severe acute respiratory syndrome

Introduction to severe acute respiratory syndrome Severe Acute Respiratory Syndromes, also known as SARS, is a new respiratory infection caused by SARS coronavirus infection. It is mainly transmitted by close-range air droplets, with fever, headache, muscle aches, fatigue, dry cough and less sputum as the main clinical manifestations. In severe cases, respiratory distress may occur. The disease is highly contagious and has significant aggregation in families and hospitals. basic knowledge The proportion of illness: 0.0002% Susceptible people: no special people Mode of infection: respiratory transmission Complications: pneumonia, pulmonary edema

Causes of severe acute respiratory syndrome

Coronavirus infection (50%):

On April 16, 2003, WHO announced the cause of Severe Acute Respiratory Syndrome (SARS) based on the results of a collaborative study conducted by 13 laboratories in 11 countries and regions including the Chinese mainland and Hong Kong, Canada, and the United States. Coronavirus, called SARS-associated coronavirus (SARS-CoV), coronavirus is a type of single-stranded positive-strand RNA virus. Under electron microscope, the envelope of the virus has a protuberance or crown shape. Therefore, it was named in 1968. In 1975, the International Virus Nomenclature Committee decided to establish coronaviridae, which is a Coronavirus. In 1993, according to the serological characteristics of the virus, replication and genomic homology, The genus Orbivirus is also listed as a coronavirus family. In addition, it has also been found that the artervirus originally belonging to the family of the togaviridae has a certain relationship with the coronavirus family. Coronaviruses include human coronavirus and pig infection. Gastroenteritis virus, porcine hemagglutinating encephalomyelitis virus, cat intestinal coronavirus, dog, cow, rabbit coronavirus and avian infectious bronchitis virus It causes respiratory and digestive tract and nervous system diseases in humans and animals. They only infect vertebrates. Human respiratory tract coronavirus (HCoV-0C43) and human intestinal coronavirus (HcoV-229E) are mainly caused by human upper respiratory tract. Infection and diarrhea, the new coronavirus discovered this time will add a new type to human coronavirus in taxonomy. Clinical specimens of patients with severe acute respiratory syndrome can be isolated from Vero E6 cells in vitro to isolate SARS coronavirus. Under the electron microscope, the virus particles are 80-140 nm in diameter, surrounded by drum-like coronal processes. The interval between the protrusions is wide, and the shape of the virus is coronal, showing the typical characteristics of coronavirus.

The SARS coronavirus is a single-stranded positive-strand RNA virus. From the complete genome sequencing of several strains that have been completed, the genome has a total length of 29206 to 29727 nucleotides, with little difference and higher amino acid homology. Chinese scholars have found that the S protein (spike protein) and M protein (membrane protein) of SARS virus have strong variability, and these two proteins help the virus enter human cells, which means that future vaccine research may Difficulties encountered, phylogenetic relationship phylogenetic tree analysis shows that SARS virus proteins are quite different from known human and animal coronaviruses and belong to a new class of coronaviruses. SARS virus can be cultured in Vero cells and monkey kidney cells. Cytopathic changes can occur in Vero cells for 5 days. In the rough endoplasmic reticulum and vesicles of the cells, viral particles are visible on the surface of the plasma membrane and outside the cells, and the SARS virus is inoculated into monkeys.

The same clinical manifestations and pathological changes may occur as humans. SARS coronavirus is more resistant and stable to other human coronaviruses. It can live for up to 4 days on dry plastic surfaces, at least 1 day in urine, and patients with diarrhea. At least 4 days in the feces, cultured at 4 ° C for 21 days, good storage stability at -80 ° C, but lost the infection when exposed to common disinfectants or fixatives, heated to 56 ° C every 15 min can kill The 10000U virus, SARS virus-specific IgM and IgG antibodies appear 10 to 14 days after onset, IgM antibodies reach a peak in the acute phase or early recovery, disappear after about 3 months, IgG antibodies can be in the third week of the disease The titer was high, and the high titer continued after 3 months. The experiment proved that the antibody may be a protective antibody and can neutralize the virus particles isolated in vitro.

Pathogenesis

At present, the pathogenesis of severe acute respiratory syndrome is still unclear, and viremia can occur in the early stage of onset. The pathogenicity of cells can be observed during the isolation of virus culture in vitro. It is speculated that SARS virus in humans may be involved in lung tissue cells. There is a direct damage effect, however, lymphocytes decrease during the onset of SARS patients, CD4 and CD8 T lymphocytes are significantly decreased, indicating that cellular immunity may be impaired, and clinical application of corticosteroids can improve lung inflammation and reduce clinical symptoms. Therefore, it is currently considered that the immune damage induced by SARS virus infection is the main cause of the disease. The pathological changes of the lungs are obvious, the lungs are obviously inflated, and the lesions are mainly diffuse alveolar lesions, with pulmonary edema and transparency. Membrane formation, 3 weeks after the disease, alveolar internalization and pulmonary interstitial fibrosis, resulting in alveolar fiber occlusion, microvascular thrombosis and pulmonary hemorrhage in small blood vessels, scattered lobular pneumonia, alveolar epithelial shedding, hyperplasia and other diseases, hilar Lymph nodes are more congested, bleeding and lymphoid tissue is reduced.

Severe acute respiratory syndrome prevention

The focus is on controlling the source of infection and cutting off the route of transmission.

1. Control the source of infection

(1) Epidemic situation report: China has included Severe Acute Respiratory Syndrome in the first of the Class B legal infectious diseases implemented by the Law of the People's Republic of China on the Prevention and Control of Infectious Diseases on December 1, 2004, and provides for reporting according to Class A infectious diseases. Isolation treatment and management, when discovering or suspecting the disease, report to the health and epidemic prevention agency as soon as possible to achieve early detection, early isolation and early treatment.

(2) Isolation and treatment of patients: clinically diagnosed cases and suspected diagnosed cases should be inspected and treated separately according to respiratory infectious diseases in designated hospitals, and can be considered for discharge if they meet the following requirements:

1 body temperature is normal for more than 7 days.

2 respiratory symptoms improved significantly.

The 3X chest radiograph showed significant absorption.

(3) Isolation and observation of close contacts: For medical observation cases and close contacts, if the conditions permit, they should be in isolation at the designated place for 14 days. When receiving isolation observation at home, pay attention to ventilation and avoid close contact with family members. Medical observation by the health and epidemic prevention department, daily measurement of body temperature, if found to meet the suspected or clinical diagnostic criteria, immediately transferred to a designated hospital by special means of transportation.

2. Cut off the route of transmission

(1) Comprehensive prevention of the community: carry out scientific popularization of the disease; reduce large-scale mass gatherings or activities, maintain ventilation and air circulation in public places; eliminate hidden dangers of sewage discharge system in residential buildings; The public places where you have stayed are fully disinfected.

(2) Maintain good personal hygiene habits, do not spit, avoid sneezing, coughing, cleaning the nose in front of people, and wash your hands afterwards; ensure ventilation in your home or activity place; wash your hands frequently; avoid going to crowded or relatively closed places If you have respiratory symptoms such as cough, sore throat, or when you need to go out to the hospital and other places, you should wear a mask; avoid close contact with people.

(3) The hospital should set up a fever clinic to establish a special channel for the disease. The ward where the severe acute respiratory syndrome is admitted should be provided with a clean area without cross-section, a semi-polluted area and a contaminated area; the ward, office, etc. should be well ventilated. Suspected patients and clinically diagnosed patients should be treated separately from the ward. Inpatients should wear masks and should not leave the ward freely. Patients should not be accompanied, and should not visit. The ward office and other building spaces in the ward, the surface of the ground and the surface of the object, used by the patient. Articles, medical supplies, and patients' excretions and secretions must be fully and effectively cleaned in strict accordance with the requirements. When medical personnel and other staff members enter the ward, they must do a good job of personal protection and wear 12 layers of cotton yarn. Masks or N95 masks, hats and eye shields, gloves, shoe covers, etc., wear isolation gowns, so that no body surface is exposed to the air, wash hands after touching patients or other contaminated items.

3. Protect the susceptible population to maintain an optimistic and stable attitude, balance the diet, drink more soup, keep warm, avoid fatigue, adequate sleep and exercise in the open space. These good habits can help improve the human body. The resistance of acute respiratory syndrome, there is no effective preventive drug to choose from, the passive prevention of the disease in patients with recovery has not been reported, China has developed horse anti-virus serum for SARS coronavirus and The preventive effect of inactivated vaccines that are inoculated nasally remains to be verified.

Severe acute respiratory syndrome complications Complications Pneumonia pulmonary edema

Concurrent with heart, liver and kidney damage, and also found secondary bacterial infection in the lungs.

Severe Acute Respiratory Syndrome Symptoms Common Symptoms Severe Acute Respiratory Syndrome Irregular Heat Relaxation Heat Nasal Fecal Hypoxemia Hypoxic Difficultness Breathing Shock

The incubation period is 1 to 16 days, usually 3 to 5 days. The onset is urgent, with fever as the first symptom, which may have chills, body temperature often exceeds 38 ° C, irregular heat or relaxation heat, heat retention, etc. For 1 to 2 weeks; accompanied by headache, muscle aches, general weakness and diarrhea, often no nasal congestion, runny nose and other symptoms of the upper respiratory tract, 3 to 7 days after onset of dry cough, less sputum, occasional bloodshot sputum, lung signs Not obvious, some patients can smell a little wet voice, the disease reaches a peak in 10 to 14 days, fever, fatigue and other symptoms of infection poisoning, and frequent cough, shortness of breath and difficulty breathing, a little activity, asthma, palpitations, being Forced to rest in bed, this period is prone to secondary infection of the respiratory tract, after the course of 2 to 3 weeks, the fever gradually subsides, other symptoms and signs are alleviated or even disappeared, the absorption and recovery of lung inflammation changes are slower, after the body temperature is normal It takes about 2 weeks to fully absorb and return to normal. Light-weight patients have mild clinical symptoms and short course of disease. Severe patients have serious illness and rapid progress, and are prone to respiratory distress syndrome. The condition of children is milder than that of adults. Not content with first symptom of fever, especially those with a history of recent surgery or patients with underlying diseases.

Severe acute respiratory syndrome test

1. Blood routine: The white blood cell count is usually normal or decreased in the early to middle stages of the disease, lymphocytes are usually reduced, platelets are also reduced in some cases, CD3, CD4 and CD8 T cells are significantly reduced in T cell subsets, and can return to normal in later stages of disease. .

2. Blood biochemical examination: Alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and its isoenzymes can be increased to varying degrees, and blood gas analysis can be found to reduce blood oxygen saturation.

3. Serological detection: Indirect fluorescent antibody method (IFA) and enzyme-linked immunosorbent assay (ELISA) have been established in China to detect SARS virus-specific antibodies in serum. The preliminary application results show that the two methods are sensitive to the detection of IgG-type antibodies. 91%, specificity is about 97%, IgG type antibody detection rate is low or not detected in the first week after onset, the detection rate is more than 80% at the second weekend, more than 95% at the third weekend, and the titer Continued to rise, still maintain a high titer in the third month after the disease.

4. Molecular biological detection: Reverse transcription polymerase chain reaction (RT-PCR) method is used to examine the RNA of SARS coronavirus in blood samples, respiratory secretions, stools and the like.

5. Cell culture to isolate virus: The patient specimen is inoculated into the cell for culture, and after the virus is isolated, the SARS virus should also be identified by RT-PCR.

Imaging examination: Most patients have chest X-ray abnormalities in the early stage of onset, mostly patchy or reticular changes, often appear as single lesions in the early stage of the disease, and the lesions increase rapidly in the short term, often involving the lungs or Single lung and multiple leaves, some patients progress rapidly, with large-scale shadows, and the surrounding areas of the lungs are more common, while pleural effusion, cavity formation and hilar lymph node enlargement are less common, and there is no lesion on the chest radiograph. Clinically suspected patients with this disease, chest X-ray examination should be reviewed within 1 to 2 days. Chest CT examination is most common with glass-like changes, lung shadow absorption is absorbed, and dissipation is slow; shadow changes and clinical symptoms and signs may sometimes be inconsistent.

Diagnosis and diagnosis of severe acute respiratory syndrome

diagnosis

Because the pathogen detection method and its diagnostic value are still in the development and verification stage, there is currently a relatively mature laboratory diagnosis method with specificity, sensitivity and early diagnosis. Severe acute respiratory syndrome must be in comprehensive epidemiology. Based on the history, clinical manifestations, preliminary laboratory tests and diagnostic treatments, the following clinical diagnosis is established. The following is the diagnostic criteria for severe acute respiratory syndrome issued by the Ministry of Health of China in May 2003.

1. Diagnosis basis

(1) Epidemiological data

1 Have a close contact with the affected person or one of the infected groups, or have evidence of a clear infection.

2 Within 2 weeks before the onset of illness, I have been to or live in an area where severe acute respiratory syndrome is reported and a secondary infection has occurred.

(2) Symptoms and signs: acute onset, fever as the first symptom, body temperature is generally higher than 38 ° C, occasionally chills; may be associated with headache, joint pain, muscle aches, fatigue, diarrhea; often no upper respiratory tract Symptoms; may have cough, mostly dry cough, less sputum, occasional blood sputum; may have chest tightness, severe breathing, shortness of breath, or obvious respiratory distress, lung signs are not obvious, some patients can smell a little wet Sound, or signs of lung consolidation, a small number of patients do not take fever as the first symptom.

(3) Laboratory examination: peripheral blood leukocyte counts generally do not increase or decrease; often the number of lymphocytes decreases.

(4) Chest X-ray examination: the lungs have different degrees of flaky, patchy infiltrating shadows or reticular changes, some patients progress rapidly, with large-scale shadows; often multi-leaf or bilateral changes, shadows Absorption and dissipation are slower; lung shadows and symptoms and signs may be inconsistent. If the test results are negative, it should be reviewed after 1 to 2 days.

(5) Antibacterial therapy has no obvious effect.

2. Diagnostic criteria

(1) Suspected diagnosis: Comply with the above diagnosis (1) (2) (3), or 2) (3) (4), or (2) (3) (4).

(2) Clinically diagnosed cases: in accordance with (1) (2) (4) and above, or 2) (2) (3) (4), or 2) (2) (4) (5).

(3) Medical observation cases meet the above 2) (2) (3).

(4) Severe severe acute respiratory syndrome: one of the following criteria can be diagnosed as severe Severe Acute Respiratory Syndrome: 1 dyspnea, respiratory rate > 30 beats / min; 2 hypoxemia, in oxygen 3 5L/min, arterial partial pressure of oxygen (Pa02) <70mmHg, or arterial oxygen saturation (Sp02) <93%; or can be diagnosed as acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) 3; multi-lobular lesions with lesions over 1/3 or X-ray films showing lesion progression >50% within 48 hours; 4 shock or multiple organ dysfunction syndrome (MODS); 5 with severe underlying disease, or with other infections Sexually transmitted diseases, or age >50 years old.

3. Diagnostic significance of laboratory-specific pathogen detection

(1) Separation of SARS virus from patient clinical specimens by cell culture method is reliable evidence of infection, combined with clinical manifestations, can make a diagnosis of illness or virus carrying, but the law cannot be used for rapid diagnosis; Under the virus, the opportunity to isolate the virus is not high, the negative result can not rule out the diagnosis of the disease; plus the technical conditions and equipment requirements are high, it is not suitable for clinical application.

(2) Detection of SARS virus nucleic acid by reverse transcription polymerase chain reaction (RT-PCR), the sensitivity of which needs to be improved; if improperly handled, it may cause nucleic acid contamination, causing false positives, when the patient repeats the same test If it is positive, or if the test is positive for different specimens, it can be clearly diagnosed as a disease or virus infection, and when the test result is negative, it cannot be used as a basis for eliminating suspected or clinically diagnosed cases.

(3) Detection of serum-specific antibodies in SARS patients by IFA and ELISA, negative in the acute phase and positive in the recovery period, or when the antibody titer in the recovery phase is 4 times or more higher than the acute phase, it can be used as a basis for determining the diagnosis. The results cannot be used as a basis for the diagnosis of this disease.

Differential diagnosis

Because of the lack of mature and reliable laboratory diagnostic methods, the diagnosis of Severe Acute Respiratory Syndrome must exclude other diseases that can explain the epidemiological history and clinical course of the patients. Clinically, it is necessary to exclude upper respiratory tract infections, influenza, bacterial or Fungal pneumonia, acquired immunodeficiency syndrome (AIDS) with pulmonary infection, legionellosis, tuberculosis, epidemic hemorrhagic fever, lung neoplasms, non-infectious interstitial lung disease, pulmonary edema, atelectasis, lung Embolism, pulmonary eosinophilic infiltration, pulmonary vasculitis and other clinical manifestations of similar respiratory diseases.

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