Influenza (Flu) is an acute respiratory infectious disease caused by the influenza virus, characterized by high infectivity, leading to millions of infections worldwide each year. This disease differs from the common cold, with features such as sudden onset, prominent systemic symptoms, and potential complications that can be life-threatening in severe cases. According to the World Health Organization, the annual global death toll from influenza-related illnesses can reach 300,000 to 500,000, highlighting its public health significance.
The influenza virus is mainly classified into types A, B, and C. Type A viruses frequently undergo genetic mutations, often causing pandemics. The disease is primarily transmitted through droplets; viral particles released during coughing or sneezing can remain in the air, and inhalation by others can lead to infection. Additionally, contact with contaminated surfaces followed by touching the mouth or nose can also cause transmission.
Influenza exhibits clear seasonal patterns, with outbreaks mainly occurring in winter in temperate regions, while in tropical areas, it may circulate year-round. Modern medicine has developed various antiviral drugs 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 cases.
The pathogen responsible for influenza is the influenza virus, mainly classified into types A, B, and C. Type A viruses frequently undergo antigenic drift due to gene reassortment of surface antigens HA and NA, leading to new subtypes. This characteristic results in a lack of widespread immunity in the population, making it the primary cause of pandemics. Type B viruses cause localized outbreaks, while type C generally causes milder symptoms.
Risk factors include age: individuals over 65 have a 5-10 times higher risk of pneumonia and complications after infection due to immune decline. Patients with underlying conditions such as heart disease, diabetes, or immunodeficiency are over three times more likely to develop severe illness. Pregnant women experience physiological changes in respiratory and immune systems, increasing risks of preterm birth or eclampsia. Healthcare workers are also at higher risk, with a 20-30% increased chance of infection due to frequent contact with patients.
Environmental factors also play a key role: crowded activities in enclosed spaces (such as transportation and large gatherings) increase transmission risk. Cold and dry environments favor virus survival, and poor indoor ventilation during winter further facilitates spread. Recent studies show that malnutrition or chronic stress can impair interferon responses, increasing infection risk by 20-30%.
Typical influenza symptoms usually appear suddenly, including a high fever above 38.3°C (sometimes up to 40°C in children), severe headache, muscle aches, and profound fatigue. These symptoms can worsen rapidly within hours, distinguishing it from the gradual onset of the common cold. Cough is usually dry initially, with minimal sputum, but may become productive after several days.
Atypical symptoms are more common in specific groups: infants may only show refusal to eat or abnormal drowsiness; elderly patients may present with altered mental status as the first symptom; immunocompromised individuals may have atypical fever curves. Some cases may exhibit gastrointestinal symptoms such as diarrhea or nausea, with a gastrointestinal flu incidence of up to 15-20% in children.
Severe complications include difficulty breathing, chest tightness, persistent nausea with vomiting, which may be signs of bacterial pneumonia or acute respiratory distress syndrome. Children with infection showing bluish skin or a respiratory rate over 40 breaths per minute require immediate medical attention. Adults with hypotension and cold sweat may have progressed to sepsis.
Clinical diagnosis primarily relies on medical history, with detailed inquiry about rapid onset, contact history, and vaccination records. Rapid antigen tests can provide results within 15 minutes but have a sensitivity of about 50-70%, often yielding false negatives. Molecular methods like RT-PCR detect viral RNA with over 95% accuracy but require 24-48 hours for results.
Laboratory diagnosis involves collecting nasopharyngeal secretions, with deep collection into the nasopharynx to ensure sample quality. Antibody tests are useful for epidemiological surveys but have limited diagnostic value for individual patients. Recent bedside rapid test kits can simultaneously detect influenza A/B and respiratory syncytial virus, aiding in differentiating pathogens.
Severe cases require chest X-ray to exclude pneumonia; blood tests may show normal or decreased white blood cell counts, with elevated C-reactive protein indicating possible bacterial coinfection. In resource-limited settings, clinicians often rely on the clinical triad (acute fever + muscle aches + respiratory symptoms) for initial assessment, with an accuracy of about 70-80%.
Supportive care forms the foundation of treatment, including antipyretics (such as acetaminophen) to control fever, and electrolyte supplementation to prevent dehydration. Muscle aches can be alleviated with non-steroidal anti-inflammatory drugs, but gastrointestinal side effects should be monitored. Severe dehydration may require intravenous fluids, with hospitalization rates around 5-10%.
Antiviral drugs like oseltamivir (Tamiflu) are most effective when administered within 48 hours of symptom onset, potentially shortening illness duration by 1-2 days and reducing complications. Zanamivir is administered via inhalation and is suitable for patients unable to take oral medication. Immunoglobulin preparations may be used prophylactically in high-risk groups, with caution for allergic reactions.
Management of complications depends on specific conditions: bacterial pneumonia requires antibiotics; respiratory failure may necessitate high-flow oxygen therapy or ventilatory support. Supportive care includes adequate rest, maintaining indoor humidity, and using humidifiers to ease respiratory discomfort. Traditional Chinese medicine adjuncts like sweating therapies should be used cautiously; excessive sweating medications are not recommended during high fever to avoid fluid loss.
Vaccination is the primary preventive strategy, with annual updates to include circulating HA antigens. Immunity develops approximately two weeks after vaccination, with an efficacy of about 40-60%, significantly reducing severe illness. It is recommended for all individuals over 6 months old, especially pregnant women, those with chronic diseases, and healthcare workers.
Non-pharmacological measures include frequent handwashing and mask-wearing. Proper handwashing involves scrubbing with soap for 20 seconds; alcohol-based disinfectants with over 60% alcohol can be used as alternatives. Droplet precautions in public places, such as coughing etiquette (covering mouth and nose with the elbow), can reduce transmission by 30-50%. Post-exposure precautions include isolating in a separate room and using personal protective equipment.
For high-risk contacts, chemoprophylaxis with oseltamivir can be considered within 48 hours of exposure, continued for 7-10 days. Achieving a vaccination coverage rate of over 70% in the population is necessary to establish herd immunity and prevent outbreaks. New mRNA influenza vaccines are under development and are expected to enhance broad-spectrum antigen coverage.
Seek immediate medical attention if you experience the following warning signs: fever lasting more than 3 days without improvement, signs of dehydration despite intravenous fluids (such as decreased urine output, dry mouth), respiratory rate exceeding normal (adults >24 breaths/min, children >30 breaths/min), or oxygen saturation below 95%. Symptoms such as chest pain with worsening breathing, altered consciousness, or seizures are also urgent.
Special populations should have a lower threshold for seeking care: infants under 6 months with any flu symptoms require medical attention, as they cannot be vaccinated. Patients with worsening chronic heart or lung diseases, such as increased angina frequency or decreased oxygen levels, should be considered urgent cases. Immunocompromised individuals should seek early medical care even with mild symptoms due to higher risk of complications, 4-6 times greater than the general population.
If medication responses are poor, such as persistent high fever despite antipyretics or worsening symptoms after initial improvement, re-evaluate with a healthcare provider. Children showing signs of Reye's syndrome (unexplained vomiting and altered mental status after fever) require immediate hospital care. Elderly patients with acute cognitive changes or gait disturbances should be evaluated for encephalitis or severe dehydration.
Influenza usually presents with sudden high fever (above 39°C), body aches, and extreme fatigue, with rapid symptom progression compared to the gradual onset of a cold. If symptoms include shortness of breath, chest pain, or altered mental status, immediate medical attention is necessary, as these may indicate complications such as pneumonia or encephalitis.
Does getting vaccinated against influenza mean I cannot get infected?The protective efficacy of the flu vaccine is about 40-60%, depending on how well the circulating strains match the vaccine. Even if infected, vaccinated individuals are less likely to develop severe illness or hospitalization. Annual vaccination is recommended to maintain immunity.
What foods should be avoided during a fever to aid recovery?Reduce intake of greasy, high-sugar, and processed foods, which can exacerbate inflammation. It is advisable to consume foods rich in vitamin C (such as oranges and red peppers), high-quality proteins (chicken breast, tofu), and mild porridge, along with adequate hydration and nutrition.
When can I resume intense exercise after recovering from influenza?Rest for at least 3-7 days after symptoms resolve, avoiding excessive cardiovascular strain. Early exercise may trigger myocarditis or other complications. Consult a healthcare provider before gradually increasing activity levels, based on physical capacity.
How can I reduce the risk of infection after contact with an influenza patient?Within 48 hours of exposure, consult a healthcare provider about the use of antiviral medications (such as oseltamivir), and reinforce hand hygiene and environmental disinfection. If symptoms develop, wear a mask and avoid public places to prevent further transmission.
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