A fast-spreading new flu variant driving a sharp rise in infections across the state is bringing with it symptoms that differ from what many people usually associate with influenza.With flu activity now classified as “very high” in Illinois, health experts say a mutated and highly contagious strain known as subclade K is changing how the illness shows up, particularly when it comes to fever patterns. One of the biggest differences doctors are seeing is how intense and long-lasting fevers have become, especially among children.“There’s more fever with the flu this year than people are used to,” said Dr. Mark Loafman, chair of Family and Community Medicine at Cook County Health, speaking to NBC Chicago. “The fever can last five to seven days, and that’s concerning. You feel sick, you don’t feel like you’re improving, and that can be worrying.”Adding to the concern, Dr. Juanita Mora, national spokesperson for the American Lung Association, as per NBC News, said some patients are finding that common fever-reducing medicines such as Tylenol or Motrin are not working as effectively. “This strain is causing very high fevers,” Mora said. “There’s also a severe cough that just doesn’t go away, a lot of phlegm, vomiting, diarrhoea, and significant joint and muscle pain.”Influenza Flu Symptoms To Watch ForVomiting has never been among the most typical flu symptoms, though it does occur more often in children. What doctors are now noticing with this strain is an increase in gastrointestinal symptoms among adults as well.“Kids with the flu often experience nausea or vomiting,” Loafman explained. “Adults usually don’t as much, but we are hearing more reports of GI symptoms in adults who have this subclade K strain.” Because of this, he said flu should not be ruled out just because stomach symptoms are present.“If you have GI issues along with body aches, fever, and respiratory symptoms, flu is still very much a possibility,” he said, adding that at-home flu tests can be useful if someone suspects they are infected.Warnings have already been issued by the Illinois Department of Public Health and several county health departments as flu-related hospital admissions and positive test results continue to climb.According to the latest state update released Monday, flu activity has reached “very high” levels, the most severe category used by the CDC to track respiratory illness trends.Health officials say most emergency room visits and hospital admissions related to respiratory illness are currently being driven by flu cases.Common Flu Symptoms To KnowFlu symptoms typically appear one to four days after exposure, according to the Cleveland Clinic.The CDC lists the following common symptoms:Fever or feeling feverish, along with chillsCoughSore throatRunny or blocked noseMuscle or body achesHeadachesFatigueVomiting and diarrhoea, which are more common in children than adultsNot everyone with the flu will develop a fever. However, health officials note that gastrointestinal symptoms are being reported more often in adults with the new strain.Influenza Flu Warning Signs To Watch ForBecause this variant is linked to higher and longer-lasting fevers, Mora said it is crucial to recognise when medical care is needed.“High fevers that don’t come down are one warning sign,” she said. “Another is trouble breathing, including wheezing, chest muscle use, or a cough that won’t stop. And dehydration is a major concern, especially if someone is barely eating or drinking.”The CDC outlines different warning signs for children and adults.In children:Rapid or laboured breathingBluish lips or faceRibs pulling in with each breathChest painSevere muscle pain or refusal to walkSigns of dehydration such as no urine for eight hours, dry mouth, or no tears when cryingLack of alertness or interactionSeizuresFever above 104°F that does not respond to medicationAny fever in infants under 12 weeksSymptoms that improve and then worsenWorsening of existing medical conditionsIn adults:Difficulty breathing or shortness of breathOngoing chest or abdominal painDizziness, confusion, or difficulty wakingSeizuresLittle or no urinationSevere muscle painExtreme weakness or unsteadinessSymptoms that return or worsen after improvingWorsening of chronic illnessesHow Long Is Flu Contagious?According to the CDC, people can spread the flu starting about one day before symptoms appear and up to seven days afterward. Most people are most contagious around three days into the illness. Young children and those with weakened immune systems may remain contagious longer.“It’s usually about five to seven days from when symptoms start before people stop shedding high levels of the virus,” Loafman said. “Ten days is very cautious, but not always necessary.”He advised masking around vulnerable people during the first week, practicing good hand hygiene, and staying home whenever possible. “If you can stay in, stay home,” he said, as per NBC News.