【Health Science】Why is influenza so deadly?

Influenza (flu) is an acute respiratory infectious disease caused by influenza virus. It usually causes many people to be infected in a certain season or time period, and has obvious seasonality. According to the World Health Organization, seasonal epidemics of influenza virus can cause an average of about 3 million to 5 million severe cases and 290,000 to 650,000 deaths related to respiratory diseases each year worldwide .

At present, we are still in the peak period of influenza, and it coincides with the return of the Spring Festival travel rush. Billions of people are moving across regions by various means of transportation, providing convenient conditions for the spread of influenza viruses.

Recently, our hospital's respiratory department admitted a middle-aged female patient with viral pneumonia. Ms. Wang (pseudonym), 45 years old, had a high fever, with the highest temperature reaching 39.0℃, accompanied by intermittent cough, severe cough accompanied by chest pain and headache , no obvious chest tightness and shortness of breath. She had been transferred to other hospitals for infusion treatment. Although her body temperature returned to normal, her cough symptoms were more severe than before .

When Ms. Wang came to our hospital for treatment, her respiratory rate was rapid . Examination revealed that her peripheral blood oxygen saturation was significantly lower than normal (about 93%). After inquiring about her medical history, the doctor learned that Ms. Wang developed cough, high fever and other discomforts after contact with a family member who had a "cold". She also had many underlying diseases , including a history of hypertension, diabetes, and coronary heart disease. She was overweight and had a history of smoking .

Considering Ms. Wang's symptoms and signs and the fact that she is currently in the peak season of influenza, the respiratory physician promptly completed respiratory virus and chest CT examinations to alert her to the possibility of viral pneumonia. The examination results showed that multiple patchy exudates were visible on chest CT, and the oxygenation was low. At the same time, the patient was at high risk of developing severe illness , and was promptly admitted to the hospital for further systematic diagnosis and treatment. Currently, Ms. Wang's oxygenation status is tending to normal.

In fact, such examples happen around us every day, and everyone begins to feel anxious and confused: "Isn't influenza just a cold?" "Why can influenza be fatal?"... Today we will learn about this "deadly influenza" together.

【 Things to know about influenza! 】

0 1What is the difference between influenza and the common cold?

Although both influenza and the common cold are respiratory illnesses, they are completely different.

The following table lists the differences between influenza and the common cold:

0 2Who are the high-risk groups for severe/critical illness?

The following groups of people are more likely to develop severe/critical cases after being infected with the influenza virus. They should be given high attention, undergo influenza virus nucleic acid testing and other necessary examinations in a timely manner, and be given antiviral drug treatment as soon as possible.

1. Children under 5 years old (children under 2 years old are more likely to develop serious complications);

2. Elderly people aged ≥ 65 years;

3. Those with the following diseases or conditions: chronic respiratory diseases, cardiovascular diseases (except hypertension), kidney diseases, liver diseases, blood system diseases, nervous system and neuromuscular diseases, metabolic and endocrine system diseases, malignant tumors, immune suppression, etc.;

4. Obese people;

5. Pregnant and perinatal women.

[Beware of influenza complications! 】

Influenza is very harmful and can easily cause serious complications, and is particularly deadly to high-risk groups.

0 1 Pneumonia

Pneumonia is the most common complication of influenza, with typical symptoms of cough with dyspnea, rapid breathing (>24 times/minute), hypoxia and fever (>3 days). Types of pneumonia include:

• Primary influenza virus pneumonia: high fever persists 3 to 5 days after the onset of influenza, as well as the above pneumonia symptoms. It is usually very serious and may progress quickly. Without active intervention, it may be life-threatening, especially for people with lung or cardiovascular diseases.

• Secondary bacterial pneumonia: After the flu symptoms have improved (including fever subsides), fever and coughing up purulent sputum reappear. Usually occurs a few days after the flu (7-14 days), the most common, accounting for about 1/3 of severe flu, and secondary Staphylococcus aureus pneumonia is often critical.

• Mixed bacterial and viral pneumonia: Referring to the above two, it can manifest as gradually worsening symptoms, or it can manifest as a brief improvement followed by worsening.

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0 2 Heart complications

Myocardial ischemia, myocardial infarction, and heart failure account for about 12% of influenza in adults, but influenza myocarditis and pericarditis are rare.

0 3 Central nervous system complications

Seizures are more common in children and patients with epilepsy, influenza-associated encephalopathy is more common in children , and influenza-induced encephalitis, cerebrovascular accidents, acute disseminated encephalomyelitis, and Guillain-Barré syndrome in adults are generally uncommon.

0 4Musculoskeletal complications

Severe myositis and rhabdomyolysis (extreme myalgia, weakness, dark urine) are more common in children. Although myalgia is a prominent feature of influenza, true myositis is uncommon.

0 5Toxic shock

During recent influenza A and B outbreaks, toxic shock-like syndromes have occurred in previously healthy children and adults, often associated with secondary toxigenic staphylococcal infections.

0 6 Co-infection

These include pneumonia (other viruses, bacteria, fungi), bacteremia, meningitis, and aspergillosis.

Influenza patients need to be vigilant if they have a fever for more than 3 to 5 days, if they have a fever again after the fever subsides, or if their symptoms continue to worsen after 3 to 5 days of illness .

【To prevent influenza, remember these! 】

0 1Vaccination

Influenza vaccination is the most effective way to prevent influenza, and can reduce the risk of influenza and serious complications. It is recommended that all people aged ≥ 6 months who have no contraindications should receive influenza vaccination.

0 2Drug prevention

Drug prevention cannot replace vaccination. It is recommended that close contacts with high-risk factors for severe/critical influenza (who have not been vaccinated or have not yet acquired immunity after vaccination) receive post-exposure drug prevention no later than 48 hours after exposure .

0 3 General Precautions

Maintaining good personal hygiene habits is an important means of preventing respiratory infectious diseases such as influenza. The main measures include:

• Wash hands frequently, keep the environment clean and ventilated, minimize activities in crowded places during the influenza season, and avoid contact with patients with respiratory infections;
• Maintain good respiratory hygiene habits. When coughing or sneezing, cover your mouth and nose with your upper arm or a tissue or towel. Wash your hands after coughing or sneezing, and try to avoid touching your eyes, nose or mouth.
• If you have flu-like symptoms, you should rest and self-isolate, and wear a mask when going to public places or seeking medical treatment.

Pay attention to your health, care for your life, and be your own first responsible person!

Information source | Department of Respiratory Medicine, Beichen Hospital, Phoenix.com, Xinhua News Agency, China Center for Disease Control and Prevention, etc.