### Date : 2024-06-22 12:22 ### Topic : Influenza #medicine #internalmedicine #infectology ---- ### Influenza Overview **Influenza**, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and, at times, can lead to hospitalization and death. The best way to prevent the flu is by getting vaccinated each year. ### Pathophysiology Influenza viruses are classified into three main types: A, B, and C. Types A and B are responsible for the seasonal flu epidemics each year. Influenza type A viruses are further divided into subtypes based on two proteins on the virus surface: **hemagglutinin(H) and neuraminidase(N)**. - **Transmission:** The flu virus spreads mainly by droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes. ### Clinical Features **Symptoms:** - **Fever or feeling feverish/chills** - **Cough** - **Sore throat** - **Runny or stuffy nose** - **Muscle or body aches** - **Headaches** - **Fatigue (tiredness)** - **Vomiting and diarrhea:** More common in children than adults. **Complications:** - **Pneumonia** - **Bronchitis** - **Sinus and ear infections** - **Exacerbation of chronic medical conditions, like asthma, heart disease, and diabetes** ### Diagnosis Diagnosis of influenza is primarily clinical, but laboratory tests can confirm the infection: 1. **Clinical Evaluation:** - Based on symptoms, especially during the flu season. 2. **Laboratory Tests:** - **Rapid Influenza Diagnostic Tests (RIDTs):** Detect viral antigens in respiratory specimens. - **Rapid Molecular Assays:** Detect viral genetic material (more accurate than RIDTs). - **RT-PCR (Reverse Transcription-Polymerase Chain Reaction):** The most sensitive and specific test for detecting influenza virus infection. - **Viral Culture:** Not commonly used for routine diagnosis but can provide detailed information about the influenza virus. ### Example Case Study **Patient Profile:** - **Name:** Jee Hoon Ju - **Age:** 35 - **Occupation:** Office Worker **Medical History:** - **Symptoms:** High fever (39°C), sore throat, body aches, headache, fatigue, and a dry cough for the past three days. **Clinical Evaluation:** - **Physical Examination:** Patient appears flushed and uncomfortable. Throat is red without exudate. Lungs are clear on auscultation, but the patient has a persistent dry cough. **Laboratory Tests:** - **RIDT:** Positive for influenza A. **Diagnosis:** Based on the clinical presentation and positive RIDT, Jee Hoon Ju is diagnosed with influenza A. ### Management 1. **Antiviral Medications:** - **Oseltamivir (Tamiflu):** Commonly prescribed, effective if started within 48 hours of symptom onset. - **Zanamivir (Relenza):** An inhaled medication, also effective within the same time frame. - **Peramivir (Rapivab):** An intravenous option for those who cannot take oral or inhaled medications. - **Baloxavir marboxil (Xofluza):** A newer antiviral, effective as a single-dose treatment. 2. **Symptomatic Treatment:** - **Rest:** To help the body fight the infection. - **Hydration:** Drink plenty of fluids to stay hydrated. - **Pain Relievers/Antipyretics:** Acetaminophen or ibuprofen to reduce fever and relieve aches. - **Cough Suppressants:** To manage persistent coughs. 3. **Preventive Measures:** - **Annual Vaccination:** The best prevention method against the flu. - **Hygiene Practices:** Frequent hand washing, using hand sanitizers, and covering mouth and nose when coughing or sneezing. - **Avoid Close Contact:** With people who are sick and staying home when you are sick to prevent spreading the flu. ### Prognosis - **Uncomplicated Influenza:** Most people recover within a week or two without requiring medical treatment. - **Complicated Influenza:** High-risk groups, such as young children, elderly individuals, pregnant women, and people with chronic health conditions, may develop complications and require medical intervention. - **Mortality:** Most deaths occur in those with underlying health conditions or the elderly. ### Conclusion Influenza is a common respiratory infection with potentially serious complications, especially in high-risk populations. Annual vaccination, good hygiene practices, and prompt antiviral treatment are crucial in managing and preventing the spread of influenza. Early diagnosis and supportive care can significantly improve outcomes and reduce the burden of the disease. --- ### Highly Infective Season for Influenza **Seasonality:** - Influenza typically follows a seasonal pattern, with peak activity occurring during the colder months. This pattern varies by geographical region: - **Northern Hemisphere:** Influenza season usually occurs from late fall to early spring, peaking between December and February. - **Southern Hemisphere:** Influenza season typically runs from May to September, peaking in June and July. - **Tropical Regions:** Influenza can occur year-round, with some countries experiencing two peaks, one during the rainy season and another during the cooler months. ### Appropriate Vaccination Period **Timing for Vaccination:** - The optimal time for influenza vaccination is before the start of the flu season, allowing the body enough time to develop immunity. - **Northern Hemisphere:** - Vaccination is generally recommended to begin in early fall, ideally by the end of October. - Vaccinations can continue to be given as long as flu viruses are circulating and unexpired vaccine is available. - **Southern Hemisphere:** - Vaccination campaigns often start in late March or early April, ahead of the peak flu season. - **Tropical Regions:** - Vaccination timing can vary, and local health authorities may provide specific recommendations based on regional influenza activity patterns. **Effectiveness:** - It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. - Annual vaccination is necessary because flu viruses evolve rapidly, and vaccine formulations are updated each year to match the most current circulating strains. ### Example Case Study: Vaccination Timing in the Northern Hemisphere **Patient Profile:** - **Name:** Jee Hoon Ju - **Age:** 45 - **Occupation:** Office Worker - **Location:** Seoul, South Korea (Northern Hemisphere) **Vaccination Period:** - **Ideal Timing:** Jee Hoon Ju should aim to get vaccinated in early October to ensure protection before the flu season peaks. - **Continued Availability:** If he misses the early October window, he can still receive the flu vaccine later in the fall or winter, as long as the flu viruses are circulating and vaccines are available. ### Special Considerations **High-Risk Groups:** - The following groups are at higher risk of developing complications from influenza and should be prioritized for vaccination: - **Children aged 6 months to 5 years** - **Pregnant women** - **Elderly individuals (65 years and older)** - **People with chronic medical conditions (e.g., asthma, diabetes, heart disease)** - **Healthcare workers and caregivers** **Types of Vaccines:** - **Inactivated Influenza Vaccine (IIV):** Given as an injection, suitable for most people. - **Live Attenuated Influenza Vaccine (LAIV):** Given as a nasal spray, recommended for healthy individuals aged 2-49 years, except for pregnant women and those with certain medical conditions. - **Recombinant Influenza Vaccine (RIV):** An option for those with egg allergies, as it is not produced using eggs. **Vaccine Strain Selection:** - Each year, the World Health Organization (WHO) and national health authorities recommend the specific strains to be included in the flu vaccine based on surveillance data and predictions about which strains will circulate in the upcoming season. ### Conclusion Influenza vaccination is crucial for preventing the spread of the virus and protecting individuals, especially those at high risk of complications. The timing of vaccination is essential to ensure optimal protection before the flu season peaks. In the Northern Hemisphere, vaccination is ideally done by the end of October, while in the Southern Hemisphere, it is recommended before the start of the flu season in April. Annual vaccination is necessary due to the evolving nature of the influenza virus.