Influenza is an acute respiratory infectious disease caused by the influenza virus, characterized by high infectivity and seasonal outbreaks worldwide. The disease primarily spreads through droplets, with common symptoms including fever, muscle aches, and fatigue. Severe cases may lead to complications such as pneumonia or cardiac issues, posing significant threats to high-risk groups. According to the World Health Organization, approximately 3 to 5 million people worldwide are infected with influenza each year, with severe cases reaching 3 to 5 million.
The influenza virus is classified into types A, B, and C. Type A viruses are prone to antigenic drift due to genetic characteristics, necessitating annual updates of the vaccine. The disease is most active during winter to early spring, with crowded places such as schools and offices becoming hotspots for transmission. The incubation period after infection is usually 1 to 4 days, with contagiousness lasting 3 to 7 days, facilitating rapid spread within families and communities.
The primary source of infection is patients in the acute phase. The virus spreads directly through droplets from coughs or sneezes, and contact with contaminated surfaces followed by touching the mouth or nose can also cause infection. The antigenic variations of surface proteins HA and NA in Type A influenza viruses prevent the development of lasting immunity, leading to recurrent outbreaks. High-risk groups include individuals over 65 years old, pregnant women, patients with cardiovascular or respiratory diseases, and immunocompromised individuals. These groups have a 3 to 5 times higher risk of developing severe illness after infection.
During replication within host cells, the virus induces cytokine storms, resulting in fever and systemic malaise. Environmental factors such as low temperature and dry climate may increase viral survivability, and indoor airflow circulation from air conditioning can facilitate droplet transmission. Recent studies indicate that obese individuals, due to metabolic abnormalities and chronic inflammation, have a 20-30% increased risk of severe illness after influenza infection.
Typical symptoms usually appear suddenly, including a rapid rise in body temperature above 38.3°C, muscle aches, and severe headache. Some patients may exhibit symptoms similar to the common cold, such as sore throat and dry cough, but the high fever and systemic discomfort are distinguishing features of influenza. In children, symptoms may include diarrhea or abdominal pain, while elderly individuals may only show lethargy or decreased appetite.
Clinical diagnosis mainly relies on symptom assessment and epidemiological history, such as contact history and outbreak clusters. Rapid antigen tests can confirm the virus within 15 minutes but have a sensitivity of about 50-70%. Laboratory diagnosis often uses RT-PCR technology to accurately identify virus subtypes and resistance genes, which typically takes 24-48 hours.
Doctors evaluate using the "Influenza Rapid Diagnostic Criteria." If symptoms include fever accompanied by cough or sore throat during the influenza season, a clinical diagnosis can be made. Severe cases require chest X-rays and erythrocyte sedimentation rate tests to assess for pneumonia or sepsis complications.
The main treatment currently involves neuraminidase inhibitors (such as oseltamivir), which should be used within 48 hours of symptom onset to significantly shorten the disease course. Supportive therapies include antipyretics and hydration; severe dehydration may require intravenous fluids. Hospitalization is usually reserved for respiratory failure or organ failure, possibly requiring ventilator support or extracorporeal membrane oxygenation (ECMO).
Antiviral drugs should be chosen based on circulating virus types; for example, strains resistant to oseltamivir may require zanamivir. Patients with pneumonia should undergo bacterial cultures to determine if antibiotics are necessary, but unnecessary antibiotic use should be avoided to prevent resistance.
Vaccination is the primary preventive measure. The annually updated vaccine covers major circulating strains such as H1N1 and H3N2. After vaccination, protection begins approximately two weeks later and can last 6 to 8 months. Hand hygiene with alcohol-based hand sanitizers or proper handwashing can reduce infection risk by 30-50%. High-risk groups should avoid crowded places during flu season and wear surgical masks.
If high fever exceeds 39°C and persists for more than 3 days, or if there are symptoms such as difficulty breathing or chest pain, immediate medical attention is necessary. Patients with chronic diseases whose symptoms worsen within 48 hours—such as uncontrolled blood sugar in diabetics or swelling in cardiac patients—should seek professional evaluation promptly. Infants with rapid breathing (over 40 breaths per minute) or inability to feed should be considered emergency cases.
Special situations include:
Even with mild symptoms, individuals who have had contact with confirmed cases and belong to high-risk groups should seek medical attention within 24 hours of symptom onset to maximize treatment efficacy.
It takes about two weeks after vaccination for sufficient antibodies to develop in the body. It is recommended to vaccinate 1 to 2 months before the start of the flu season. Since viral strains may vary each year, the World Health Organization updates vaccine components based on circulating trends. Therefore, annual vaccination is advised to maintain protection.
Why do influenza symptoms sometimes suddenly worsen? How can I tell if I need to see a doctor immediately?Influenza can lead to complications such as pneumonia or encephalitis, causing rapid deterioration of symptoms. If high fever persists for over three days, or if symptoms include difficulty breathing, confusion, chest pain, or bloody sputum, immediate medical attention is required. These symptoms may indicate the virus has invaded the lungs or other organs, necessitating early antiviral treatment or hospitalization.
When is the correct time to take oseltamivir (Tamiflu)? Is self-medication risky?Oseltamivir should be taken within 48 hours of fever onset or symptom appearance to effectively inhibit viral replication and shorten the illness duration. Self-medicating without medical guidance may result in missing the optimal treatment window or using the drug in patients with contraindications such as renal impairment, which could cause side effects or resistance issues.
Is complete bed rest necessary during influenza? Does moderate activity help recovery?During fever, it is advisable to reduce physical exertion, but light activities such as short walks can promote circulation and prevent muscle atrophy or thrombosis from prolonged bed rest. The key is to avoid strenuous exercise, adjust activity levels according to physical capacity, and ensure adequate hydration and nutrition.
How can I reduce the risk of infection after contact with an influenza patient? What are the isolation measures?Within 48 hours of contact, consult a doctor about prophylactic antiviral medication. Also, reinforce hand hygiene and avoid sharing utensils. If infected, wear a mask, cover mouth and nose when coughing, and disinfect frequently touched surfaces with bleach. Isolation should continue until fever subsides for at least 24 hours.
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