Influenza is an acute respiratory infectious disease caused by the influenza virus, characterized by high contagion and seasonal outbreaks worldwide. The disease is primarily transmitted through respiratory droplets, with common symptoms after infection including fever, muscle aches, and fatigue. In severe cases, it may lead to pneumonia or heart problems, posing a significant threat to specific high-risk groups. According to the World Health Organization, approximately 3 to 5 million people are infected with influenza globally each year, with severe cases reaching 300,000 to 500,000.
The influenza virus is classified into three types: A, B, and C. Type A viruses are prone to antigenic drift due to genetic characteristics, necessitating annual updates to vaccines. The disease is most active during the winter to early spring, with crowded places such as schools and offices becoming hotspots for transmission. The incubation period after infection is typically 1 to 4 days, and the infectious period can last from 3 to 7 days, allowing influenza to spread rapidly within families and communities.
The main source of influenza transmission is patients in the acute phase, with the virus spreading directly through droplets from coughing or sneezing. Touching contaminated surfaces and then touching the mouth or nose can also lead to infection. The antigenic changes in surface proteins HA and NA of type A influenza viruses result in a lack of lasting immunity in the population, making repeated outbreaks a key factor. High-risk groups include individuals aged 65 and older, pregnant women, patients with cardiopulmonary diseases, and those with immune system deficiencies, who are 3 to 5 times more likely to develop severe illness after infection compared to the general population.
When the virus replicates within host cells, it can induce a cytokine storm, leading to fever and general malaise. Environmental factors such as low temperatures and dry climates may increase the virus's survival time, while air circulation in air-conditioned rooms also facilitates droplet transmission. Recent studies indicate that obese individuals have a 20-30% increased risk of severe illness after influenza infection due to metabolic abnormalities and chronic inflammatory states.
Typical symptoms usually appear suddenly, including a sharp rise in body temperature above 38.3°C, widespread muscle aches, and severe headaches. Some patients may exhibit symptoms similar to the common cold, such as sore throat and dry cough, but the characteristic high fever and systemic discomfort of influenza can help differentiate the two. In children, infection may present as diarrhea or abdominal pain, while older adults may only show signs of lethargy or decreased appetite.
Clinical diagnosis primarily relies on symptom assessment and epidemiological history, such as exposure history and outbreak situations. Rapid antigen tests can confirm viral antigens within 15 minutes, but sensitivity is around 50-70%. Laboratory diagnosis often employs RT-PCR technology to accurately identify viral subtypes and resistance genes, which typically takes 24-48 hours.
Physicians will evaluate based on the "Influenza Rapid Diagnostic Criteria"; if symptoms align with fever accompanied by cough or sore throat, and it is during the influenza season, a clinical diagnosis can be made. Severe patients require chest X-rays and erythrocyte sedimentation rate tests to assess complications such as pneumonia or sepsis.
Currently, neuraminidase inhibitors (such as Oseltamivir) are primarily used for treatment and should be administered within 48 hours of symptom onset to significantly shorten the duration of the illness. Supportive therapy includes antipyretics and fluid replacement, with severe dehydration patients possibly requiring intravenous fluids. Hospital treatment is usually aimed at patients with respiratory failure or organ failure, who may need mechanical ventilation or extracorporeal membrane oxygenation (ECMO).
Antiviral medications should be chosen based on the circulating virus type; for example, strains resistant to Oseltamivir may require Zanamivir instead. Patients with pneumonia complications should undergo bacterial cultures to determine the need for antibiotic treatment, while being cautious to avoid unnecessary antibiotic use that could lead to resistance issues.
Vaccination is the primary preventive measure, with annually updated vaccines covering major circulating strains such as H1N1 and H3N2. The vaccine takes effect approximately 2 weeks after administration and provides protection for 6 to 8 months. In terms of hand hygiene, using alcohol-based hand sanitizers or proper handwashing can reduce infection risk by 30-50%. High-risk groups should avoid crowded places during the outbreak season and wear surgical masks.
If high fever exceeds 39°C and persists for more than 3 days, or if there are warning symptoms such as difficulty breathing or chest pain, immediate medical attention should be sought. Chronic disease patients whose symptoms worsen within 48 hours, such as diabetic patients with uncontrolled blood sugar or heart disease patients experiencing edema, require prompt professional evaluation. Infants showing rapid breathing (over 40 breaths per minute) or inability to eat should be treated as emergencies.
Special circumstances include:
Even if symptoms are mild, individuals who have been in contact with confirmed cases and belong to high-risk groups should seek medical attention within 24 hours of symptom onset to maximize treatment opportunities.
It takes about 2 weeks after receiving the influenza vaccine for the body to produce sufficient antibodies, so it is recommended to get vaccinated 1 to 2 months before the start of the influenza season. Because the virus strains may mutate each year, the World Health Organization updates the vaccine components based on epidemic trends, so it is advised to get vaccinated annually to maintain immunity.
Why do influenza symptoms suddenly worsen? How can one determine if immediate medical attention is needed?Influenza can lead to complications such as pneumonia or encephalitis, causing symptoms to deteriorate rapidly. If high fever persists for more than 3 days, or if there are symptoms such as difficulty breathing, confusion, chest pain, or blood-tinged sputum, immediate medical attention should be sought. Such symptoms may indicate that the virus has invaded the lungs or other organs, necessitating early use of antiviral medications or hospitalization.
What is the correct timing for taking Oseltamivir? Are there risks associated with self-medication?Oseltamivir should be taken within 48 hours of fever or symptom onset to effectively inhibit viral replication and shorten the duration of the illness. Self-medication may pose risks due to missed timing for optimal treatment or lack of medical evaluation for contraindications such as renal function abnormalities, which could lead to side effects or resistance issues.
Is complete bed rest necessary during influenza? Does moderate activity help recovery?During fever, it is advised to reduce physical exertion, but light activities such as short walks can help promote circulation and prevent muscle atrophy or thrombotic risks from prolonged bed rest. The key is to avoid vigorous exercise and adjust activity intensity based on physical condition, while also ensuring adequate hydration and nutrition.
How can one reduce the risk of infection after contact with an influenza patient? What isolation measures are recommended?Within 48 hours after contact, one can consult a physician about taking prophylactic antiviral medications, while also enhancing hand hygiene and avoiding sharing utensils. If already infected, patients should wear masks, cover their mouth and nose when coughing, and use bleach to clean frequently touched surfaces, isolating themselves for at least 24 hours after fever resolution.
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