Influenza symptoms explained as US braces for ‘catastrophic’ K variant

These are the symptoms of influenza to watch for as the US braces for a new flu strain that has sparked a global surge in cases.

If there's one thing you can count on this time of year, it's people getting ill. And it appears flu season has started early in some countries, with Canada, Australia, the UK, and Japan among those reporting rising cases.

The influx is driven by a strain called subclade 'K' of H3N2, a variant of influenza A, CNN reports. Now, respiratory illness is increasing across the US following holiday gatherings, and Christmas is just around the corner.

A UK A&E consultant told The Independent that the flu is spreading so rapidly in hospitals that it is 'by far the worst winter that we have had in my time as a consultant', adding: "Without a shadow of a doubt, in the last three weeks, it has gone from a bad winter to this is beyond catastrophic."

And things aren't looking better in the US either.

Influenza season is on the rise around the world (Halfpoint Images/Getty Images)

At least 14 US regions report moderate to high flu activity, particularly in the Northeast, and flu cases in New York began rising two weeks earlier than usual, with flu hospitalizations having doubled each week for two weeks, according to Dr James McDonald, commissioner of the New York State Department of Health.

A map from the Center for Disease Control and Prevention (CDC) also showed which states had been hardest hit, with data indicating an 8.1 per cent rise in cases.

What are the symptoms of influenza?

Influenza is a viral infection of the throat, nose, and lungs that can spread rapidly. The key difference between the flu and a cold is that symptoms typically appear within two or three days of exposure to the virus.

In contrast, colds typically develop more gradually, and people will feel much worse with the flu than with a cold.

Mayo Clinic has flagged eight main symptoms to be aware of. These include:

• Sore throat
• Runny or stuffy nose
• Fever
• Cough
• Headache
• Muscle aches
• Feeling very tired
• Sweating and chills

Most people can manage symptoms at home with rest, fluid and painkillers. But if you're vulnerable, it's important to seek help right away to prevent complications.

The flu can worsen pre-existing health conditions, like asthma (Handsome Bob/Getty Images)

What complications can influenza cause?

Those with health conditions such as asthma, heart disease, diabetes or a weakened immune system are considered vulnerable. So too are people over the age of 65, children and pregnant women.

More serious complications of influenza can include lung infections such as pneumonia, airway inflammation such as bronchitis, and sepsis, a life-threatening reaction to infection.

Other potential complications can include toxic shock syndrome, acute respiratory distress syndrome, and rhabdomyolysis, or muscle damage.

It can also worsen pre-existing chronic conditions, such as asthma and kidney problems.

Influenza puts pressure on the respiratory system (Pocketlight/Getty Images)

When should you see a doctor for influenza?

Mayo Clinic also warns of several emergency symptoms of the flu that require urgent medical attention.

In adults, these might present as:

• Trouble breathing or shortness of breath
• Chest pain or pressure
• Ongoing dizziness
• Hard to wake up or confusion
• Dehydration
• Seizures
• Worsening of existing medical conditions
• Severe weakness or muscle pain

Children might see the same symptoms, as well as:

• Fast breathing or ribs that pull in with each breath
• Gray or blue lips or nail beds
• No tears when crying and a dry mouth, along with not needing to urinate
• Symptoms, such as fever or cough, that get better but then come back or get worse

If you have any concerns, it is advised to seek medical help immediately.