How long are you contagious with flu? The answer might be longer than you think

With flu cases surging in Illinois as a new and mutated variant rapidly spreads, mitigating spread of those who contract the virus is increasingly important. But how long are you actually contagious with flu?

The answer could be longer than you think.

According to Dr. Mark Loafman, the chair of Family and Community Medicine at Cook County Health, those with flu should ideally stay home for up to 10 days.

“It’s about five to seven days from the symptom onset before you stop really shedding high levels of the virus. So 10 days is perfect, but it really doesn’t need to be that long,” Loafman said. “Again, we recommend wearing a mask around anybody who’s vulnerable or if you’re in a crowded place for that first seven days. And, you know, absolutely great hand washing hygiene so you’re not spreading the virus around. And if you can stay in, stay home.”

Those with flu are most contagious around three days into their infection, according to the Centers for Disease Control and Prevention, but some people, like young children and those with weakened immune systems, may be contagious for longer, however.

Flu can be detected in infected persons at least one day before symptoms begin, and up to seven days after. Loafman suggests using an at-home test if you suspect you might have flu so you can know how contagious you might be.

Flu levels in Illinois

Already at the start of January, cases in Illinois are at “very high” levels as a mutated and highly contagious variant known as “subclade K” takes hold.

The Illinois Department of Public Health and numerous health departments across Chicago-area counties have issued warnings as hospital admissions and positive tests for influenza soar in the state.

The bulk of hospital admissions and ER visits associated with respiratory illnesses were made because of flu symptoms, according to officials.

And experts warn “we haven’t peaked yet.”

“The question is, where will it peak?” Loafman said, adding that the current levels are “not unexpectedly high, but again, it could spread.”

“These are contagious viruses and people are indoors and we’ve had a lot of holiday travel and people together. So we would expect this spike would continue over the next few weeks,” he said.

Dr. Santina Wheat, a family physician with Northwestern Medicine, shared similar thoughts in an interview with NBC Chicago, explaining an uptick in cases might occur within the next week as children head back to school.

Illinois also on Monday reported its first influenza death in a child this season.

Symptoms changing with new variant

“Subclade K” has brought a change in telltale signs of the virus, experts said.

Among the most prominent is the level of fevers being reported, particularly in children.

“More fever with the flu this year than people are accustomed to. And the fever can last up to seven days, so five to seven days. And that’s worrisome,” Dr. Mark Loafman, the chair of Family and Community Medicine at Cook County Health, told NBC Chicago. “You feel ill, you feel sick, and you worry that you’re not getting better.”

What’s more, Dr. Juanita Mora, the national spokesperson for the American Lung Association, said in some cases, fevers aren’t responding to typical treatments like Tylenol or Motrin.

“This new strain has symptoms of really high fevers. It has a really bad cough that won’t go away, very phlegmy, and also vomiting and diarrhea and lots of joint aches as well as muscle aches,” Mora said.

While vomiting isn’t the most common of symptoms associated with flu, it can be seen more often in pediatric cases. But with the new variant, doctors have reported more instances of adults experiencing GI issues.

“Children with flu do often have GI symptoms – nausea, vomiting – adults less often, but we are seeing anecdotally more signs of some GI illness for the adults who have the subclade K strain of flu,” Loafman said, adding that he “wouldn’t exclude flu if you have GI symptoms and have the other symptoms like body aches, fever, upper respiratory symptoms.”

Rose O’Keeffe, a Chicago resident who recently recovered from the flu, said she experienced a fever every single day, a rollercoaster of body aches and congestion.

Flu symptoms typically begin within one to four days of exposure, according to the Cleveland Clinic.

The CDC reports the following symptoms for those with flu:

• fever* or feeling feverish/chills
• cough
• sore throat
• runny or stuffy nose
• muscle or body aches
• headaches
• fatigue (tiredness)
• some people may have vomiting and diarrhea, though this is more common in children than adults

*It’s important to note that not everyone with flu will have a fever

Again, health officials warn that GI symptoms are increasing, particularly in adults, with the new strain, however

Warning signs to watch for

Because the new strain is bringing higher and longer lasting fevers, Mora said it’s important to know the warning signs to seek medical attention.

“One is those high fevers that won’t break,” she said. “Two, the other thing, is any signs of shortness of breath. So when kids or adults are having trouble breathing, they start using their chest muscles, they start wheezing audibly, they start having a cough that won’t go away. That’s a sign to go to the ER. And the third sign I always teach patients: dehydration. So when a kid is hit very hard with the flu or an adult, especially older adults, they don’t want to eat or drink so they’re just laying in bed but that can be very dangerous.”

According to the CDC, the warning signs are different in children and adults.

They include:

In children

• Fast breathing or trouble breathing
• Bluish lips or face
• Ribs pulling in with each breath
• Chest pain
• Severe muscle pain (child refuses to walk)
• Dehydration (no urine for 8 hours, dry mouth, no tears when crying)
• Not alert or interacting when awake
• Seizures
• Fever above 104 degrees Fahrenheit that is not controlled by fever-reducing medicine
• In children younger than 12 weeks, any fever
• Fever or cough that improve but then return or worsen
• Worsening of chronic medical conditions

In adults

• Difficulty breathing or shortness of breath
• Persistent pain or pressure in the chest or abdomen
• Persistent dizziness, confusion, inability to arouse
• Seizures
• Not urinating
• Severe muscle pain
• Severe weakness or unsteadiness
• Fever or cough that improve but then return or worsen
• Worsening of chronic medical conditions

Vaccines

“Illinois is facing a significant winter surge in seasonal respiratory illnesses with flu activity at very high levels,” Dr. Sameer Vohra, IDPH director, said in a statement. “Vaccinations remain the most effective tool to prevent severe illness from flu, COVID-19 and RSV.”

Loafman and Mora agreed, saying while this season’s flu vaccine was not formulated specifically for the new variant, it will still help prevent against more severe illness.

And it’s not too late, they said.

“There has been a lot of talk about the fact that the new variant is not well-covered by it. … That is true, but you still get protection. And so what we typically see, the folks that are sick, hospitalized, are those who were not vaccinated. … The vaccine isn’t perfect. It doesn’t protect all aspects of this from folks. It doesn’t keep you necessarily from getting the flu as often as we would like, but it certainly mitigates the severity of illness,” Loafman said. “So people with [the] flu shot tend to do better. Their symptoms are less likely to get worse. They’re more likely to bounce back and recover and stay well and far less likely to be hospitalized or, God forbid, to die from the flu if you’ve had the vaccine. And it’s never too late to get it until the flu season’s over – so late March, April, sometime like that.”

Loafman said even those who have already had the flu should consider getting the vaccine if they haven’t already as the risk for reinfection also exists.

“There are three strains going around and probably a few more. So you can still be protected from the future,” he said.

In Chicago, residents can get a flu shot by visiting any one of the city’s immunization clinics. A full list can be found here.

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