Causes and Risk Factors of Cold and Flu

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While many people confuse colds and the flu or use the terms interchangeably, they’re actually caused by different viruses. Colds are caused by a variety of viruses, whereas flu is specifically caused by the influenza virus.

Common Causes

Both colds and the flu are caused by viruses that spread from person to person through respiratory droplets (for example, through coughing or sneezing) but different viruses are responsible for the two conditions. Influenza virus causes the flu, while a number of viruses can cause the common cold.

Causes of the Common Cold

Many viruses can prompt cold symptoms—like runny nose, headache, and cough—but rhinoviruses are the most common.

Other viruses that cause colds include:

Causes of Flu

There are four different types of flu viruses, and not all of them cause disease in humans. The four primary types of flu are: 

  • Influenza A: Influenza A viruses cause the bulk of flu cases each flu season, and the severity of the season often depends on which A strain is circulating. The two A strains currently affecting people are influenza A(H3N2) and influenza A(H1N1)
  • Influenza B: These viruses can also contribute to outbreaks during the flu season though often to a lesser extent than A strains. Infections by influenza B viruses tend to be less severe than A strains, but they can still be dangerous, especially for young children. The subtypes of influenza B circulating among humans come from just two lineages: B/Yamagata and B/Victoria.
  • Influenza C: Influenza C can affect humans but is generally mild and uncommon.
  • Influenza D: This strain is believed to affect only animals, primarily cattle. 

Flu viruses change frequently, making it difficult for the body to learn how to fight them effectively. Flu vaccines are updated every year to include the A and B strains most likely to cause epidemics that flu season.

Risk Factors

Certain things can increase your chances of getting colds or the flu, including environmental factors that make it easier for the viruses to spread and medical conditions that affect the body’s ability to protect itself.

Environmental Risk Factors

Both cold and flu viruses are spread through things like cough, sneezing, or wiping your nose and touching objects or other people. As a result, certain situations or environments can make it easier for viruses to spread from person to person. These include:

  • Crowded spaces: When a person infected with flu coughs or sneezes, the flu virus can travel up to 6 feet away. Frequenting places where a lot of people come in close contact with one another—such as train stations, schools, or nursing facilities—increases your chances of coming in contact with cold or flu viruses, especially during the wintertime.
  • Shared surfaces: Cold and flu viruses can live on surfaces for hours, making shared objects like doorknobs and handrails prime real estate for viruses looking to find their next host.
  • Sanitary conditions: When you’re infected with cold or flu viruses and wipe or blow your nose, the viruses get onto your hand or tissue and, from there, can transfer to other people or objects. Spending a lot of time in places where you can’t wash your hands or where surfaces aren’t frequently disinfected can increase your chances of becoming infected yourself.

Health Risk Factors

Not everyone exposed to cold or flu viruses will get sick. Sometimes the body is able to fight off an infection early to prevent any symptoms from appearing.

Some people are more likely to get seriously sick with the flu (or other respiratory illnesses) because of their age, medical history or vaccination status. 

  • Age: Young children and older adults are more susceptible to getting sick with colds and flu and are particularly vulnerable to experiencing serious complications.
  • Medical history: Some medical conditions can make it harder for your body to fight off diseases or be exacerbated by colds and the flu. Pregnant women and those with asthma, heart disease, diabetes, HIV infection, cancer, or certain neurologic conditions are more likely than others to get severely sick with diseases like the flu.
  • Vaccination status: No vaccine exists to prevent colds, but there is one for the flu. Forgoing the annual flu vaccine (recommended for everyone over 6 months old) can increase your risk of getting seriously sick with the flu. In fact, roughly 80% of kids who died from the flu in recent years had not been vaccinated, and research shows getting vaccinated can cut a healthy child’s risk of dying from flu by nearly two-thirds.

Cold and the flu might share a lot of symptoms, but they are caused by different germs. Understanding the different viruses and how they can be prevented could help you protect yourself from getting sick, as well as help you develop an effective treatment plan with your doctor if you do become infected.

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