This winter, the United States is grappling with what experts are calling a "quad-demic" — a rare and concerning surge of four viruses spreading at the same time.
Flu, COVID-19, respiratory syncytial virus (RSV) and norovirus are all circulating at high levels, creating a perfect storm for hospitals and public health.
The Centers for Disease Control and Prevention has reported that all four viruses are circulating at "high" or "very high" levels across the country.
Emergency room visits have surged in recent weeks, fueled by rising cases of influenza and RSV, according to the CDC. ER visits for COVID-19 have also increased since the fall. Unfortunately, there's no relief in sight, as the CDC warns that respiratory illness activity will remain high for several more weeks.
Influenza, COVID-19, and RSV share several common symptoms, including fever, cough, sore throat, fatigue and muscle aches. Other common symptoms include congestion, runny nose and headache. However, each virus has some distinct features: influenza often causes more intense muscle or body aches, COVID-19 can lead to a new loss of taste or smell and RSV may cause wheezing and difficulty breathing. These viruses can range from mild to severe, and their impact varies depending on the individual and their age group.
Meanwhile, norovirus is spreading at its highest levels since 2019, according to recent data. This highly contagious virus is causing widespread outbreaks with individuals experiencing intense stomach discomfort, nausea, vomiting, diarrhea and fever.
"This year, the number of reported norovirus outbreaks have exceeded the numbers that we've seen recently and in the years before the pandemic," a CDC spokesperson told ABC News.
With flu season in full swing, COVID cases climbing, RSV affecting both children and the elderly, and norovirus causing widespread stomach illness, it's clear that this winter is shaping up to be one of the most challenging in recent years.
The simultaneous spread of these viruses is adding to the challenges healthcare providers are already facing. The overlap of these illnesses, each with their own sets of symptoms and at-risk populations, means that healthcare workers are stretched thin and hospital beds are becoming harder to come by in some areas. The sheer number of people seeking care for various illnesses has raised concerns about how much more the healthcare system can withstand this winter.
"What we're seeing now is that the hospitals near 100% capacity almost all the time, and when you add an extra 100 patients with respiratory viral disease who otherwise would not be there if this wasn't respiratory viral season, you really tax the system," Dr. Scott Roberts, medical director of infection prevention at Yale New Haven Health, told ABC News. "We're seeing very full emergency rooms with waits to get into the hospital because of that."
People are being urged to take precautions, including getting vaccinated for flu and COVID-19, practicing good hygiene, and staying home when sick to help alleviate some of the burden.