According to the information currently available, influenza A (H1N1) is an acute respiratory infection caused by the mutated new influenza A (H1N1) virus. Through droplets, aerosols, direct contact or indirect contact transmission, the main clinical manifestations of flu-like symptoms, a few cases of heavy disease, rapid progress, can appear viral pneumonia, combined with respiratory failure, multiple organ function damage, serious cases can lead to death. As this influenza A (H1N1) is a new disease, its characteristics remain to be further observed summary.
A. Pathogenesis
Influenza A (H1N1) virus belongs to the orthomyxoviridae (0rthomyxoviridae), influenza A virus genus (Influenza virus A). Typical virus particles are spherical, 80nm-120nm in diameter, with a capsule membrane. The vesicle membrane has many radially arranged protruding glycoproteins, namely erythrocyte hemagglutinin (HA), neuraminidase (NA) and matrix protein M2.
The virus is a single-stranded negative-stranded RNA virus with a genome of about 13.6 kb, consisting of 8 independent fragments of different sizes. The virus is sensitive to ethanol, iodine volt and tincture of iodine; it is heat sensitive and can be inactivated at 56℃ for 30 minutes.
II. Epidemiology
By 8:00 a.m. Beijing time on May 8, 2009, a total of 24 countries and regions in the world appear to have confirmed cases of influenza A (H1N1) 2371 cases, distributed in the Americas, Europe, Oceania and Asia. Among them, Mexico confirmed 1112 cases, 42 deaths; the United States confirmed 896 cases, 2 deaths; China’s Hong Kong Special Administrative Region confirmed 1 case. Except for Mexico and the United States, no fatal cases were reported in other countries and regions.
(A) the source of infection.
Influenza A (H1N1) patients as the main source of infection. Although pigs have been found in the body of influenza A (H1N1) virus, but there is no evidence that animals as the source of infection.
(B) the transmission route.
Mainly through droplets or aerosol transmission through the respiratory tract, but also through the oral cavity, nasal cavity, eyes and other places where the mucous membrane directly or indirectly contact transmission. Contact with the patient’s respiratory secretions, body fluids and objects contaminated with the virus may also cause transmission.
(iii) Susceptible people.
The population is generally susceptible.
Clinical manifestations and auxiliary examinations
The incubation period is usually 1-7 days, mostly 1-4 days.
(A) Clinical manifestations.
1, manifested as flu-like symptoms, including fever (axillary temperature ≥ 37.5 ℃), runny nose, nasal congestion, sore throat, cough, headache, myalgia, fatigue, vomiting and/or diarrhea.
2. Complications such as pneumonia may occur. In a few cases, the disease progresses rapidly and respiratory failure, multi-organ insufficiency or failure occurs.
3, the patient’s original underlying disease can also be aggravated.
(B) Laboratory tests.
1. Peripheral blood picture: total white blood cell count is usually not high or reduced.
2.Pathogenetic examination
(1) viral nucleic acid detection: RT-PCR (preferably using real-time RT-PCR) method to detect respiratory specimens (pharyngeal swabs, oral rinses, nasopharyngeal or tracheal extracts, sputum) in the influenza A (H1N1) virus nucleic acid, the results can be positive.
(2) virus isolation: respiratory specimens can be isolated from the influenza A H1N1 virus. Combined with viral pneumonia when the lung tissue can also be isolated from the virus.
3, serological examination: dynamic detection of serum influenza A (H1N1) virus-specific neutralizing antibody level is 4 times or more than 4 times elevated.
(C) other ancillary tests.
Chest imaging and other examinations can be performed according to the condition. When combined with pneumonia, patchy inflammatory infiltrative shadow is seen in the lungs.
Diagnosis
The diagnosis of this disease is mainly combined with epidemiological history, clinical manifestations and pathogenic examination, early detection and early diagnosis is the key to prevention, control and treatment.
(A) Suspected cases.
A suspected case can be diagnosed if one of the following conditions is met.
1, within 7 days before the onset of influenza A (H1N1) suspected or confirmed cases of close contact (in the absence of effective protection conditions to take care of patients, and patients living together, exposed to the same environment, or direct contact with the patient’s airway secretions or body fluids), the emergence of influenza-like clinical manifestations.
2, within 7 days before the onset of influenza A (H1N1) epidemic (the emergence of sustained human transmission of the virus and community-based levels of epidemics and outbreaks) of the country or region, the emergence of influenza-like clinical manifestations.
3, the emergence of influenza-like clinical manifestations, positive test for influenza A virus, but further testing to exclude the pre-existing subtypes.
(ii) Confirmed cases.
The presence of influenza-like clinical manifestations, along with one or more of the following laboratory test results.
1, positive nucleic acid detection of influenza A (H1N1) virus (real-time RT-PCR and RT-PCR can be used).
2, isolated to the influenza A (H1N1) virus.
3, serum influenza A (H1N1) virus-specific neutralizing antibody level is 4-fold or more elevated.