Overview of Influenza
Influenza is an acute respiratory infectious disease caused by influenza viruses mainly manifested as high fever, headache, fatigue and generalized muscle aches and pains, etc. Sore throat, runny nose and other respiratory symptoms are less severe due to the body infected with influenza viruses, which can be treated with general treatment, symptomatic treatment, etiologic treatment and traditional Chinese medicine treatment.
Definition
Influenza (influenza for short) is an acute respiratory infection caused by influenza virus.
It is highly contagious and spreads quickly.
Influenza viruses mutate easily and it is difficult to obtain lasting immunity.
Typing
Types according to symptoms
Simple Influenza: The most common type of influenza, which can be cured on its own and usually takes 1 to 2 weeks.
Pneumonic influenza: This is a combination of influenza viral pneumonia with severe coughing, sputum, shortness of breath and other symptoms, which can be life-threatening.
Gastrointestinal influenza: symptoms include fever, vomiting, abdominal pain, diarrhea, etc. It is relatively rare, mostly occurs in children, and can be recovered in 2 to 3 days.
Toxic influenza: very rare, with high fever, shock, respiratory failure, neurological damage, diffuse intravascular coagulation, etc., with a high mortality rate.
According to the virus type subtypes
Influenza A
Influenza A is caused by influenza A virus infection.
Often causes pandemics and severe illness.
It is very susceptible to mutation, which occurs mainly in the hemagglutinin (H) and neuraminidase (N) on the surface of the virus. Influenza A viruses can be categorized into different subtypes based on the mutation of these two elements.
The most common subtypes include H5N1 (preferred by elderly patients), H1N1 (preferred by children), and H7N9 (preferred by the elderly, especially those with diabetes and chronic obstructive pulmonary disease).
Influenza B
Caused by influenza B virus infection.
The main host is human.
Mutation is slow and often leads to localized outbreaks, not pandemics.
Influenza C
Caused by influenza C virus.
Natural hosts include humans and pigs.
Generally does not mutate and can cause disseminated epidemics, more common in children.
Incidence
Source of infection
Primarily patients with influenza, followed by those with latent infection.
Influenza viruses can be transmitted from 2 days before the onset of symptoms to about 1 week after the onset of symptoms, up to 10 days or more in children, with the most contagious being the first 2 to 3 days of illness.
Route of transmission
It is mainly spread by droplets in the air.
It can also be spread through person-to-person contact or contact with contaminated objects (such as tableware, towels, tea sets, etc.).
Susceptible people
The population is generally susceptible.
Antibodies appear 1 week after infection or vaccination, peak in 2 to 3 weeks, begin to decline after 1 to 2 months, and drop to a lower level in about 1 year.
The following groups are more likely to develop severe disease.
Children younger than 5 years of age.
Elderly people older than 65 years of age.
Pregnant women.
People with chronic diseases such as diabetes, tuberculosis and anemia.
Obese people [Body Mass Index greater than 30, BMI = weight (kg)/height (m) squared].
People who use immunosuppressive drugs (e.g. glucocorticoids) for a long time.
People with immunodeficiency diseases (e.g. acquired immunodeficiency syndrome).
Epidemic characteristics
Influenza is highly prevalent, with many outbreaks occurring worldwide, and annual incidence rates of about 5% in adults and 20% in children.
Worldwide, there are up to 3-5 million cases of severe illness and 250,000-500,000 deaths per year, and the number of deaths may be higher if new virus subtypes emerge.
The onset of influenza is seasonal, often occurring in winter and spring in northern China and throughout the year in southern China.
The mortality rate of seasonal influenza is usually less than 0.1%, which is related to whether or not the patient receives treatment and the level of medical care.
Causes
Causes
Influenza is caused by infection with influenza virus.
Pathogenesis
Influenza viruses invade the cells of the respiratory tract and replicate, then are released from the cells to infect more cells and repeat the process.
It can cause cell degeneration, necrosis and shedding, and if it invades the lungs, it can also cause lung congestion and edema.
Symptoms
Influenza has an incubation period of one to three days, with a minimum of a few hours and a maximum of four days.
Symptoms of influenza are usually more severe than those of the common cold.
Simple Influenza
The onset of illness is rapid.
The main manifestation is high fever and chills, and the body temperature can reach 39～40℃, which peaks 1～2 days after the onset of the disease, and gradually decreases after 3～4 days. Headache, fatigue, loss of appetite and generalized muscle pain can also be seen.
Accompanying symptoms: often accompanied by cough, nasal congestion, runny nose, dry and sore throat, hoarseness and so on. Among them, runny nose and dry and sore throat are often mild or insignificant.
If there is no complication, the fever can subside 3 to 4 days after the onset of the disease, and other symptoms mostly improve with it, but coughing and recovery of physical strength often take 1 to 2 weeks; those with mild cases can recover in 2 to 3 days.
Gastrointestinal influenza
Fever.
Nausea, vomiting.
Abdominal pain, diarrhea.
Loss of appetite.
Recovery in 2 to 3 days.
Pneumonia type influenza
Initially similar to simple influenza.
The condition worsens after 1～2 days and may have the following manifestations.
High fever that does not go away.
Violent cough with bloody or purulent sputum.
Shortness of breath, cyanosis.
Extreme fatigue, etc.
Toxic influenza
High fever that does not go away.
Decrease in blood pressure.
Delirium.
Convulsions.
Shortness of breath with pallor, cyanosis and irritability.
Complications
Secondary bacterial pneumonia
The incidence is 5% to 15%. The disease further worsens 2 to 4 days after the onset of influenza, or instead worsens after the recovery period of influenza, with high fever, severe cough, purulent sputum, and dyspnea.
Rachel’s syndrome
Occasionally seen in children under 14 years old, especially those who use salicylic acid antipyretic and analgesic drugs such as aspirin.
The main manifestations are nausea and vomiting after fever reduction, followed by neurological symptoms such as drowsiness, coma and convulsions.
Heart damage
Uncommon, mainly myocarditis, pericarditis.
Involving the myocardium, there may be discomfort in the precordial area, palpitation, shortness of breath, and in severe cases, arrhythmia and heart failure may occur.
Involvement of the pericardium, may appear behind the sternum knife cutting pain, as well as dyspnea, pallor and so on.
Myositis and rhabdomyolysis
Rare in influenza, the main symptoms include muscle pain, swelling, pressure, weakness, etc.
Neurological damage
A variety of neurologic injuries can complicate encephalomyelitis, transverse myelitis, viral meningitis, focal neurologic dysfunction, acute infectious demyelinating polyneuropathy, and other neurologic injuries.
Consultation
Department of Medicine
Respiratory Medicine
When high fever, chills, muscle aches, fatigue, headache, accompanied by sore throat, cough, runny nose, etc. occur, it is recommended to consult a doctor promptly.
Emergency Department
When there is high fever that does not go away, severe cough, shortness of breath, or even convulsions, agitation, cyanosis, etc., it is recommended to go to the Emergency Department immediately.
Preparation for medical treatment
Preparation for medical consultation: registration, preparation of information, common problems
Tips for seeking medical treatment
Chest X-ray or chest CT is often needed, so avoid wearing clothes made of metal, and those who are pregnant or planning to be pregnant should inform the doctor in time.
Avoid taking fever-reducing medicines or antibiotics by yourself before going to the doctor, so as not to influence the doctor’s judgment of the condition. For patients with fever, physical cooling, such as applying cold compresses to the forehead and wiping the hands, feet and armpits with warm water, is preferred.
Preparation Checklist for Doctor’s Visit
Symptom Checklist
Particular attention should be paid to the time of onset of symptoms, special manifestations, etc.
Is there fever? What is the highest degree?
Is there a cough? How long has the cough lasted?
Is there any sputum? What kind of phlegm?
Is there nasal congestion or runny nose?
How long have the symptoms been present?
Medical History Checklist
Has there been any contact with a person with the flu?
Checklist
Test results for the last 6 months to bring to the doctor’s office
Laboratory tests: routine blood test, C-reactive protein, blood biochemistry, influenza virus nucleic acid test
Imaging tests: Chest X-ray, Chest CT scan
List of medications
Medication used in the last 3 months, bring the box or package if available
Antiviral drugs: oseltamivir, acyclovir, ganciclovir
Antipyretics: ibuprofen, acetaminophen
Nasal decongestants: pseudoephedrine drops
Others: Ambroxol, dextromethorphan
Diagnosis
Diagnosis is based on
Medical history
Possible exposure to a person with influenza.
Clinical manifestations
Symptoms
Presence of more typical symptoms such as high fever, chills, muscle aches, malaise, and headache with sore throat, cough, and runny nose.
Physical signs
Acute appearance with flushed cheeks and visible pharyngeal congestion.
Respiratory sounds are coarsened or rales are present, and pleural friction sounds are occasionally heard.
Laboratory tests
Blood test, C-reactive protein measurement
Blood counts can help to determine the status of infection, including whether there is a bacterial infection; C-reactive protein can help to determine whether there is a bacterial infection and its severity.
The total number of white blood cells is usually low or decreased, and lymphocytes are elevated, or can be elevated in severe cases. In severe cases, lymphocytes may also be elevated. In cases of bacterial infection, the total number of white blood cells and neutrophils will be elevated, and C-reactive protein will be elevated.
Fasting is not required before the test.
Blood biochemistry
It can be performed to understand the condition of liver, heart and other important organs, and is suitable for people with more serious conditions.
Hypokalemia may be present in some cases, and creatine kinase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, creatinine, etc. may be elevated in a few cases.
Fasting is required before the test.
Arterial blood gas analysis
In severe cases, hypoxemia and respiratory failure may occur, and the severity can be determined by arterial blood gas analysis.
There may be a decrease in partial pressure of oxygen, oxygen saturation, oxygenation index, and acid-base imbalance.
Serologic examination
The main purpose is to determine the antibodies in the serum during the acute and recovery periods.
Commonly used methods include hemagglutination inhibition test and complement binding test.
Antibody titers with more than 4-fold elevation or single test antibody titers > 1:80 are diagnostic.
The diagnosis is confirmed when the level of influenza virus-specific IgG antibody in both acute and recovery sera is 4-fold or more elevated.
Pathogenetic examination
It mainly includes virus isolation and culture, viral antigen and nucleic acid test, viral antigen and nucleic acid test can be used for early diagnosis.
The diagnosis can be confirmed if any one of the influenza virus nucleic acid test, antigen test or isolation culture is positive.
The main method of viral nucleic acid testing is the polymerase chain reaction, which has the best specificity and sensitivity, and can quickly differentiate between viral types and subtypes, and results are usually obtained within 4 to 6 hours.
Specimens are nasopharyngeal or tracheal secretions, sputum, etc.
Imaging
Chest X-ray, CT
The presence and severity of lung inflammation and specific lesions can be recognized.
It may show signs of bronchial infection with increased bronchial texture, and in severe cases, there may be infiltrative lesions in the lungs or pleural effusion, or even fusion into patches.
The examination is radiologic and requires breathing in conjunction with the physician’s instructions during the examination.
Differential Diagnosis
Common cold
Similarities: Both may present with fever, malaise, loss of appetite, runny nose, cough and sore throat.
Differences: The common cold is mainly characterized by nasal congestion, runny nose, sneezing, etc. Systemic symptoms (fever, muscle aches, etc.) are milder than those of influenza; pathogenetic tests can help to differentiate.
Other upper respiratory tract infections
Similarities: Sore throat, cough, fever and other symptoms.
Differences: other upper respiratory tract infections, such as acute pharyngitis, tonsillitis, rhinitis, sinusitis, etc., the symptoms are mainly confined to the infected area, which can be manifested as hoarseness, itchy throat, etc., and the symptoms of fever are relatively milder; etiologic tests can help identify them.
Other lower respiratory tract infections
Similarities: Fever, cough, sputum, malaise and other symptoms may occur.
Differences: Other lower respiratory tract infections include acute tracheobronchitis and mycoplasma pneumonia. They can be differentiated by pathogenetic tests. Mycoplasma pneumonia agglutination test and MG streptococcus agglutination test can be positive.
Treatment
General treatment
Isolation
Influenza is highly contagious and anyone suspected or diagnosed should be actively isolated.
The room should be ventilated and maintained at a suitable temperature and humidity.
Respiratory support
It is used for those who have symptoms such as dyspnea, or whose examination reveals severe or critical illness such as hypoxemia.
Depending on the severity of hypoxia, conventional oxygen therapy, nasal cannula high-flow oxygen therapy, non-invasive ventilation or invasive mechanical ventilation can be chosen, and extracorporeal membrane oxygenation can be used if necessary.
Others
Pay attention to rest, especially in the acute stage, when symptoms such as fever and malaise are more serious.
Drink plenty of water, increase nutrition, choose calorie-rich and easily digestible food.
Symptomatic treatment
Antipyretics, such as acetaminophen, may be used for fever. Avoid salicylic acid drugs such as aspirin in children to avoid triggering Reye’s syndrome.
People with nasal congestion can use drugs to reduce nasal mucosal congestion and antihistamines, such as pseudoephedrine hydrochloride, chlorpheniramine maleate.
For coughing and phlegm, cough suppressants and expectorants such as dextromethorphan, compound licorice, guaifenesin, etc. may be used.
If it may be combined with bacterial or fungal infections, antibiotics or antifungal drugs, such as cephalosporins, should be used in accordance with medical advice.
All medications should be used in accordance with the doctor’s instructions, and should not be adjusted or discontinued on their own.
Etiologic treatment
Antiviral treatment.
Timing of treatment
Drugs are effective when administered within 48 hours of the onset of illness, as they can relieve symptoms, shorten the duration of illness, reduce complications such as pneumonia, and lower hospitalization and mortality rates.
Antiviral drugs are not mandatory, and the risks and benefits should be fully evaluated, and careful consideration should be given to whether to give antiviral treatment.
Antiviral drugs against influenza
Three types of drugs are currently on the market: neuraminidase inhibitors (e.g., oseltamivir, zanamivir, paramivir), hemagglutinin inhibitors (e.g., abidol), and M2 ion channel blockers (e.g., amantadine, amantadine).
Neuraminidase inhibitors
Indicated for influenza A and B.
Oseltamivir: Also used for influenza A and B prophylaxis, but does not prevent complications. Administered orally. Appropriate dose reductions are needed for severe renal insufficiency.
Zanamivir: Not for use in children under 7 years of age. Inhalation is required. Persons with chronic respiratory disease are at higher risk of bronchospasm and should use with caution.
Paramivir: Intravenous infusion only. Verapamil may be administered intravenously in critically ill patients and in those who cannot take the drug orally.
Hemagglutinin inhibitors
Such as Abidol, can be used for the treatment of influenza A and B in adults. However, the clinical application in China is less.
M2 ion channel blockers
Such as amantadine, amantadine, only against influenza A virus.
They are resistant to most strains of influenza virus and are no longer recommended by the Centers for Disease Control and Prevention (CDC).
All medications should be used in accordance with your doctor’s instructions and should not be adjusted or discontinued on your own.
Traditional Chinese Medicine (TCM)
Proprietary Chinese medicines
Chinese patent medicines are used to relieve wind, clear away heat and detoxify the toxin.
Commonly used are Jinhua Qingfen Granules, Lianhua Qingdian Capsules (granules), Qingkailing Granules (capsules, soft capsules, tablets, oral solution, etc.), Shufeng Xiexue Capsules, Yinqiao Xiexue Tablets (granules, combinations, etc.), Sangju Cold and Flu Pills (tablets, granules, etc.), and so on.
Traditional Chinese Medicine (TCM)
The treatment needs to be recognized by a professional physician.
Formulas that may be used include Yin Qiao San combined with Sang Ju Drink plus and minus, Ma Xing Shi Gan Tang plus and minus, Xuan Bai Cheng Qi Tang plus and minus, Ginseng and Forsythia Tang plus and minus, Sha Shen and Maimendong Tang plus and minus, and so on.
Prognosis
Cure
The disease is self-limiting, and if there are no complications, it can be self-cured after 3 to 14 days.
A small number of cases may develop into serious illnesses, and in severe cases, the condition may be life-threatening due to respiratory failure.
Hazards
Influenza can present with symptoms such as high fever and malaise, which can interfere with normal life.
Influenza is contagious and can spread to others.
Special populations such as the elderly, infants and young children, pregnant women, and immunocompromised people are prone to develop serious illnesses, which can be life-threatening if not treated in time.
Daily
Daily Management
Daily management
Influenza is highly contagious. Avoid close contact with others, especially children, the elderly, pregnant women and immunocompromised people.
Wear a mask and cover your nose and mouth when sneezing to prevent spreading.
Stay at home and rest in bed during the fever period to reduce physical exertion. After the fever subsides, activities can be resumed gradually.
Quit smoking and avoid passive smoking to prevent aggravating lung damage.
Ensure sufficient sleep time and avoid exertion and late nights.
Ventilate the room and keep the temperature and humidity at a suitable level to minimize cold air and other stimuli and prevent cold.
Dietary management
During the fever period, it is advisable to choose calorie-rich, light and easy-to-digest food and drink more water.
Mainly consume high-quality protein foods (150-200 grams per day), such as lean meat, fish, shrimp, eggs, soybeans, etc., and try to ensure one egg per day and 300 grams of milk and milk products.
Increase the intake of essential fatty acids through a variety of cooking vegetable oils.
Eat more fresh vegetables and fruits. More than 500 grams of vegetables per day, 200 to 350 grams of fruit per day, and choose more dark-colored fruits and vegetables.
Prevention
Vaccination
Influenza vaccination is effective in preventing infection with the appropriate subtype of influenza virus and reducing the risk of serious complications.
There are two types of influenza vaccines: trivalent and quadrivalent.
The trivalent vaccine component contains a lineage of subtype A H3N2, subtype A H1N1, and B strains.
The tetravalent vaccine component contains two lineages of subtype A H3N2, subtype A H1N1 and type B strains.
Trivalent inactivated influenza vaccine and quadrivalent inactivated influenza vaccine have been approved for marketing in China, and are available for people 6 months of age and older if there are no contraindications. No inactivated influenza vaccine has been approved for use in infants under 6 months of age.
Contraindications to vaccination
Hypersensitivity to ovalbumin or any vaccine.
Persons with moderate to severe acute fever.
Individuals who have had Guillain-Barré syndrome.
Anyone who, in the opinion of the physician, is otherwise unable to receive influenza vaccine.
Recommended Priority Groups for Vaccination
Medical personnel, including clinical treatment personnel, public health personnel, health quarantine personnel, etc.
Vulnerable people and employees of nursing homes, long-term care facilities, welfare homes and other places where people gather.
People in key places, such as teachers and students in childcare institutions, primary and secondary schools, and detainees and staff in institutions.
Other high risk groups for influenza, including homebound elderly aged 60 and above, children aged 6 months to 5 years, people with chronic diseases, family members and caregivers of infants under 6 months of age, and pregnant women or women planning to become pregnant during the influenza season, etc.
Medication prevention
Medication prevention is not a substitute for vaccination.
Pharmacologic prophylaxis can be administered if the following conditions are met.
Elderly people, pediatricians, pregnant women, people with chronic underlying diseases and immunocompromised people who are prone to develop severe illness.
Those who have not been vaccinated or have not acquired immunity after vaccination.
Drug prophylaxis is available for those who have already been in close contact with someone with influenza.
Pharmacologic prophylaxis is given within 48 hours of exposure and can include oseltamivir and zanamivir.
Behavioral prevention
Do not come into close contact with a person who is infected with the influenza virus, and wear a mask when in contact.
Items used by people with influenza need to be sterilized. Influenza virus is not heat-resistant and can be inactivated by 100℃ for 1 minute or 56℃ for 30 minutes; it is sensitive to commonly used disinfectants (1% formaldehyde, peracetic acid, chlorine disinfectant, etc.) and ultraviolet light, and can be disinfected by ultraviolet light for 30-60 minutes daily.
Pay attention to hand hygiene, wash hands before meals and after going to the toilet, do not use hands to touch the eyes, mouth, nose and other parts of the body, and wash hands thoroughly after contacting objects with unknown hygiene conditions.
Keep indoor air circulating and maintain indoor relative humidity at 30%～80% to help reduce airborne virus suspension and inhalation.
Avoid prolonged stay in crowded places such as shopping malls and hospitals during the peak of the epidemic.
Strengthen outdoor physical exercise to improve the body’s ability to resist disease.
Pay attention to adding or subtracting clothes during fall and winter when the climate is changing.