Seasonal influenza causes between 290,000 and 650,000 respiratory-related deaths annually.
Certain groups are more likely to develop a severe influenza infection that can lead to death, including children under 5, adults 65 or older, people with chronic health conditions, and pregnant women.
But how do people die from influenza?
There are many ways people can die from the flu. Flu viruses can cause severe damage to a range of organs and systems throughout the body, including the lungs, heart, brain and overall immune system, said Dr. Akiko Iwasaki, professor of immunology and molecular, cell and developmental biology at Yale University and an investigator at the Howard Hughes Medical Institute. .
These life-threatening complications include pneumonia, which causes inflammation of the alveoli in the lungs and can cause them to fill with pus.
Influenza viruses can directly invade the lungs, causing viral pneumonia.
In addition, by damaging the cells that line the respiratory tract, viruses can open the door for bacteria in the body to grow excessively, leading to inflammation and possibly bacterial pneumonia.
“These are bacteria that typically colonize people’s upper respiratory tracts without causing any disease,” Iwasaki says. After someone gets the flu, these bacteria can gain a foothold in the lungs and multiply.
That’s partly because influenza viruses make the cells lining the respiratory tract more vulnerable to bacteria penetration and infection, so “bacteria can multiply and cause damage more easily,” according to Dr. Octavio Ramillo, chief of the division of infectious diseases at St. Jude Children’s Research Hospital.
Severe pneumonia can also lead to acute respiratory distress syndrome (ARDS), in which fluid builds up in the lungs and they become stiff and cannot expand well.
Flu complications affect not only the lungs, but also the heart. Acute myocarditis and pericarditis, respectively, cause inflammation of the heart muscles and the sac surrounding the organ. These conditions affect the heart’s ability to pump blood and disrupt its rhythm, and sometimes the consequences are fatal.
Ramelow explained that influenza infection can lead to myocarditis because influenza viruses inflame and damage the cells that line the blood vessels. The exact cause of inflammation of the pericardium (the two-layer elastic sac that surrounds the heart) is not clear, but the tissue usually becomes inflamed after a viral infection such as influenza.
In rare cases, the flu can also lead to encephalitis, or swelling of the brain. This condition can lead to serious complications including convulsions, coma, and death.
Scientists do not know exactly how influenza leads to encephalitis, but there is a hypothesis that indicates that the infection causes the body to release a flood of cytokines, which are molecules that cause inflammation. These molecules can then enter the brain because the organ’s protective barrier has been compromised, perhaps by the cytokines themselves. However, more studies are needed to confirm this theory.
The flu can also lead to sepsis, a life-threatening immune response throughout the body.
Ramelow noted that influenza viruses can trigger this immune response on their own, but they can also enable bacteria to enter the bloodstream by breaking down tissues in the body.
These blood-borne bacteria can then lead to sepsis. Some studies suggest that influenza-associated pneumonia may increase the risk of sepsis by up to six-fold, compared to influenza infection without pneumonia. However, this complication is relatively uncommon overall.
Source: Live Science
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Interview with Dr. Akiko Iwasaki, Immunologist at Yale University
Editor: Thank you for joining us today, Dr. Iwasaki. We’re discussing the serious impacts of seasonal influenza and why certain populations are more susceptible to severe complications. Can you start by explaining how influenza can lead to such high mortality rates?
Dr. Iwasaki: Thank you for having me. Seasonal influenza is a significant public health issue, causing between 290,000 and 650,000 deaths annually. The flu virus can inflict severe damage to critical organs and systems in the body, including the lungs, heart, and immune system. When it causes pneumonia, for instance, it inflates the lungs’ alveoli with pus, making breathing perilous.
Editor: That’s alarming. You mentioned pneumonia as a key complication of influenza. Can you explain how the flu virus facilitates the development of pneumonia?
Dr. Iwasaki: Certainly. The influenza virus can directly infect the lungs, leading to viral pneumonia. Moreover, it compromises the cells lining the respiratory tract, rendering them more susceptible to bacterial infections. Bacteria that usually reside harmlessly in our upper respiratory tracts can proliferate in the lungs after a flu infection. This bacterial pneumonia can become life-threatening as it overwhelms the body’s defenses.
Editor: So, the interplay between the flu virus and bacteria is crucial here. Are there other serious complications that can arise from influenza?
Dr. Iwasaki: Yes, absolutely. In severe cases, pneumonia can develop into acute respiratory distress syndrome (ARDS), which is a life-threatening condition characterized by fluid accumulation in the lungs, leading to decreased oxygenation. Furthermore, influenza isn’t just confined to the lungs; it can also cause cardiac complications such as acute myocarditis and pericarditis, which is inflammation of the heart muscle and surrounding layers.
Editor: It sounds like the flu can have widespread and severe effects on health, especially for vulnerable groups. What groups are at higher risk of experiencing these complications?
Dr. Iwasaki: The populations most at risk include young children under five, adults aged 65 and older, individuals with chronic health conditions, and pregnant women. These groups often have weaker immune responses or underlying health issues that can exacerbate the effects of influenza.
Editor: Thank you, Dr. Iwasaki, for shedding light on this crucial topic. It’s important for everyone, especially those at risk, to take preventive measures, like vaccination, to protect against influenza.
Dr. Iwasaki: Absolutely, vaccination is one of the best ways to prevent not just the flu but its potentially severe complications. Thank you for raising awareness about this.
Cases, influenza can lead to acute respiratory distress syndrome (ARDS), which is a life-threatening condition characterized by fluid accumulation in the lungs. This can result in severe breathing difficulties. Additionally, the virus can induce heart complications, such as myocarditis and pericarditis, which can disrupt heart function and even prove fatal. In rarer instances, influenza may also lead to encephalitis—swelling of the brain—which carries severe risks, including convulsions and coma. Furthermore, it can trigger a systemic immune response known as sepsis, which, while less common, can be life-threatening.
Editor: That’s incredibly concerning. Given this information, which groups should be particularly vigilant during flu season?
Dr. Iwasaki: Vulnerable populations include children under five, adults aged 65 and older, individuals with chronic health conditions, and pregnant women. These groups are at a greater risk for severe complications from influenza due to their already compromised health or unique physiological changes.
Editor: What precautions can individuals take to protect themselves and others from seasonal flu?
Dr. Iwasaki: The most effective measure is vaccination. Annual flu shots significantly reduce the risk of infection and severe outcomes. Additionally, practicing good hygiene—such as frequent handwashing, avoiding close contact with sick individuals, and staying home when feeling ill—can help curb the spread of the virus.
Editor: Thank you, Dr. Iwasaki, for shedding light on the serious impacts of seasonal influenza. Your insights are valuable as we navigate flu season.
Dr. Iwasaki: Thank you for having me. It’s crucial that we continue to communicate the importance of flu awareness and prevention.
