Influenza (Flu) is an acute respiratory infection caused by the influenza virus, characterized by high transmissibility, infecting millions of people worldwide each year. This disease differs from the common cold, with sudden onset, pronounced systemic symptoms, and severe cases potentially leading to complications or even life-threatening conditions. According to the World Health Organization, the annual death toll from influenza-related diseases can reach between 300,000 to 500,000 globally, highlighting its public health significance.
The influenza virus is mainly categorized into three types: A, B, and C. Among these, type A viruses frequently cause pandemics due to their rapid genetic mutations. The disease primarily spreads through respiratory droplets; viral particles released when an infected person coughs or sneezes can remain airborne, and those who inhale them may become infected. Additionally, touching surfaces contaminated with the virus and then touching the mouth or nose can also lead to transmission.
Influenza exhibits clear seasonal characteristics, with outbreaks occurring predominantly in winter in temperate regions, while tropical areas may experience sporadic cases year-round. Modern medicine has developed various antiviral medications and vaccines, but the rapid mutation of the virus continues to challenge public health systems. Understanding the causes, transmission routes, and preventive measures of influenza is crucial for reducing infection risks and severe illness rates.
The pathogen of influenza is the influenza virus, which is mainly divided into three types: A, B, and C. Type A viruses are prone to antigenic drift due to genetic reassortment of surface antigens HA and NA, leading to the emergence of new subtypes. This characteristic results in a lack of widespread immunity in the population, making it a major pathogen for pandemics. Type B viruses typically cause localized outbreaks, while type C viruses tend to have milder symptoms.
Risk factors include age: individuals over 65 years old have a 5-10 times higher risk of developing pneumonia after infection due to declining immune function. Patients with underlying conditions such as heart disease, diabetes, or immunodeficiency have more than three times the likelihood of severe illness compared to the general population. Pregnant women experience changes in their respiratory and immune systems, which may lead to preterm labor or eclampsia after infection. Additionally, healthcare workers are at a 20-30% higher risk of infection due to frequent contact with patients.
Environmental factors also play a crucial role: crowded activities in enclosed spaces (such as transportation and large gatherings) increase the probability of transmission. Cold and dry environments favor virus survival, and inadequate indoor ventilation during winter further promotes spread. Recent studies have shown that malnutrition or chronic stress can reduce the body's interferon response capability, increasing infection risk by 20-30%.
Typical influenza symptoms usually have a sudden onset and include a high fever above 38.3°C (children may reach up to 40°C), severe headache, muscle aches, and extreme fatigue. These symptoms can rapidly worsen within hours, contrasting sharply with the gradual onset of the common cold. Coughing is typically dry at first, with little phlegm, but may progress to a productive cough after a few days.
Atypical symptoms are more common in specific groups: infants may only exhibit refusal to eat or unusual drowsiness; elderly individuals may present with confusion as the initial symptom; immunocompromised patients may show atypical fever patterns. Some cases may present gastrointestinal symptoms such as diarrhea or nausea, with this gastrointestinal type of influenza occurring in up to 15-20% of children.
Severe complications can manifest as difficulty breathing, chest tightness, and persistent nausea accompanied by vomiting, which may indicate bacterial pneumonia or acute respiratory distress syndrome. Children who develop blue or purple skin or have a respiratory rate exceeding 40 breaths per minute require immediate medical attention. Adults who experience a drop in blood pressure accompanied by cold sweats may have progressed to sepsis.
Clinical diagnosis primarily relies on medical history collection, where physicians will inquire in detail about the suddenness of onset, contact history, and vaccination records. Rapid antigen tests can provide results within 15 minutes, but sensitivity is about 50-70%, often resulting in false negatives. Molecular biology methods such as RT-PCR can detect viral RNA with an accuracy exceeding 95%, but results take 24-48 hours to report.
During laboratory diagnosis, collecting nasopharyngeal secretions is standard procedure, requiring sufficient depth to ensure specimen quality. Antibody tests can be used for epidemiological studies, but their diagnostic value for individual patients is limited. Recently developed bedside rapid test kits can simultaneously detect type A/B viruses and respiratory syncytial virus, aiding in distinguishing different pathogens.
Severe patients require chest X-rays to rule out pneumonia, and blood tests may show normal or decreased white blood cell counts, with elevated C-reactive protein indicating possible bacterial infection. In resource-limited areas, physicians often make preliminary assessments based on the clinical symptom triangle (acute fever + muscle aches + respiratory symptoms), with an accuracy rate of about 70-80%.
Supportive care is the foundation of treatment, including antipyretics (such as acetaminophen) to control fever and electrolyte replenishment to prevent dehydration. Non-steroidal anti-inflammatory drugs can be used for muscle aches, but gastrointestinal side effects should be noted. Patients with severe dehydration may require intravenous fluid administration, with hospitalization rates around 5-10%.
Antiviral medications such as Oseltamivir must be administered within 48 hours of onset to be effective, potentially shortening the duration of illness by 1-2 days and reducing the risk of complications. Zanamivir is administered via inhalation and is suitable for patients unable to take oral medications. Immunoglobulin preparations have preventive value for high-risk groups, but allergic reactions should be monitored.
Treatment for complications must be tailored to specific conditions: bacterial pneumonia requires antibiotics, and patients with respiratory failure may need high-flow oxygen therapy or ventilator support. Supportive care includes adequate rest, maintaining indoor humidity, and using humidifiers to alleviate respiratory discomfort. Traditional Chinese medicine adjunct treatments, such as sweating therapy, should be used cautiously, as excessive use of sweating medications in febrile patients can lead to fluid loss.
Vaccination is the primary preventive strategy, with annually updated vaccines containing the HA antigens circulating that year. Immunity develops approximately two weeks post-vaccination, providing protection of about 40-60%, but significantly reducing the risk of severe illness. Recommended vaccination targets include all individuals over 6 months, especially pregnant women, chronic disease patients, and healthcare workers.
Non-pharmaceutical interventions include frequent hand washing and wearing masks. Proper hand washing requires scrubbing with soap for 20 seconds, and alcohol-based hand sanitizers with a concentration of over 60% can serve as alternatives. Droplet isolation measures in public places, such as cough etiquette (covering the mouth and nose with the elbow), can reduce transmission rates by 30-50%. Contact isolation measures after exposure to patients include private rooms and personal protective equipment.
In terms of pharmacological prevention, high-risk groups who have been in contact with patients can use Oseltamivir for chemoprophylaxis, which should be started within 48 hours of exposure and continued for 7-10 days. A collective immunity strategy requires over 70% vaccination coverage in the population to establish an immune barrier to block outbreaks. New mRNA influenza vaccines are under development, expected to enhance antigen breadth.
Immediate medical attention is required when the following warning symptoms appear: fever lasting more than 3 days without signs of subsiding, dehydration signs (such as decreased urine output, dry mouth) persisting despite intravenous fluid administration. A respiratory rate exceeding normal values by 20% (adults >24 breaths/min, children >30 breaths/min) and oxygen saturation below 95% necessitate urgent evaluation. Chest pain accompanied by worsened breathing, confusion, or seizures are also indications for emergency care.
Special groups should have a lower threshold for seeking care: infants under 6 months showing any flu symptoms should seek medical attention, as this age group cannot be vaccinated. Patients with chronic heart and lung diseases should consider it an emergency if symptoms worsen, such as increased angina frequency or decreased oxygen saturation. Immunocompromised patients should seek early medical attention even for mild symptoms, as the risk of complications is 4-6 times higher than that of the general population.
If medication treatment is ineffective, a follow-up visit is necessary, for example, if fever persists despite antipyretics, or if symptoms improve and then worsen again. Children exhibiting prodromal symptoms of Reye's syndrome (vomiting and lethargy following fever) must be taken to the hospital immediately. Elderly individuals experiencing acute cognitive dysfunction or unsteady gait should be evaluated to rule out complications such as encephalitis or severe dehydration.
Influenza typically presents with a sudden high fever (above 39°C), widespread body aches, and extreme fatigue, with symptoms worsening more rapidly than those of a common cold. If shortness of breath, chest pain, or confusion occurs, immediate medical attention is necessary, as this may indicate severe complications such as pneumonia or encephalitis.
If I get the flu after vaccination, does that mean the vaccine is ineffective?The protective efficacy of the influenza vaccine is about 40-60%, depending on the degree of viral strain variation. Even if infected, vaccination can still reduce the risk of severe illness and hospitalization, and it is recommended to get vaccinated annually to maintain immunity.
What foods should be avoided during a fever to accelerate recovery?It is advisable to reduce the intake of greasy, high-sugar, and processed foods, as these may exacerbate inflammatory responses in the body. It is recommended to consume more vitamin C (such as oranges and red peppers), quality proteins (like chicken breast and tofu), and mild porridge to replenish fluids and nutrition.
When can I resume vigorous exercise after recovering from influenza?After symptoms subside, it is advisable to rest for at least 3-7 days to avoid overloading the heart and lungs. Exercising too soon may trigger complications such as myocarditis; it is recommended to consult a physician before resuming exercise and gradually increase intensity based on physical condition.
How can I reduce the risk of infection after contact with a flu patient?Consult a physician within 48 hours of exposure to see if antiviral medications (such as Tamiflu) should be used, and enhance hand hygiene and environmental disinfection. If symptoms appear, wearing a mask and avoiding public places is essential to interrupt the transmission chain.
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