There isn’t one single new illness sweeping the country right now. What most people are catching falls into a few familiar categories: flu, COVID-19, RSV, and norovirus. RSV activity has lingered unusually late this year, with higher levels continuing into May in some regions. COVID-19 activity is low in most areas, and flu season is winding down. Here’s what’s actually circulating and how to tell which one you might have.
RSV Is Sticking Around Longer Than Usual
Respiratory syncytial virus, commonly called RSV, is the one catching people off guard this year. It typically peaks in winter and fades by spring, but the CDC has noted unusual timing this season, with elevated activity stretching into May in some parts of the country. RSV causes cold-like symptoms in most adults: congestion, cough, mild fever, and fatigue. In young children and adults over 65, it can progress to more serious lower respiratory infections like bronchitis or pneumonia.
If you’re 75 or older, the CDC recommends getting an RSV vaccine. Adults between 50 and 74 who have conditions that raise their risk of severe illness (chronic lung disease, heart disease, weakened immune systems) are also recommended to get vaccinated. It’s a single dose, not an annual shot, and it’s most effective when given in late summer or early fall before RSV season begins.
Flu Season Is Fading but Not Gone
Influenza activity has been declining nationally, with both influenza A and B trending downward. This past season saw two strains of influenza A circulating at nearly equal levels: H1N1 accounted for about 53% of subtyped cases and H3N2 made up the remaining 47%. Influenza B stayed low all season, with a small uptick later on.
The flu hits fast. You can go from feeling fine to feverish, achy, and exhausted within a day of infection. Symptoms typically appear one to four days after exposure, and you’re most contagious during the first three days of feeling sick. If you haven’t been vaccinated for this season, you’re still eligible, though the benefit decreases as the season winds down.
COVID-19 Is Circulating at Low Levels
COVID-19 activity is low across most of the country right now. The dominant variant is XFG.1.1, making up about 32% of cases, followed by a cluster of related XFG lineages. These are descendants of Omicron and, so far, don’t appear to cause a fundamentally different illness than previous variants.
COVID symptoms still overlap heavily with the flu: fever, cough, sore throat, body aches, fatigue. The distinguishing features are subtle. COVID tends to have a longer incubation period (two to five days, sometimes up to 14) compared to the flu’s one to four days. Loss of taste or smell still occurs more often with COVID than with other respiratory viruses, though it’s less common than it was with earlier variants. People with COVID are also contagious for longer, averaging about eight days after symptoms start, and they can spread the virus two to three days before they even feel sick.
Norovirus: The Stomach Bug
If your symptoms are vomiting, diarrhea, and stomach cramps rather than cough and congestion, norovirus is the likely culprit. This season’s outbreak numbers are within the normal historical range. About 1,092 outbreaks have been reported so far this seasonal year by participating states, compared to 2,430 during the same period last year. So while norovirus is circulating, it’s not at unusual levels.
Norovirus spreads incredibly easily through contaminated food, surfaces, and close contact with sick people. It comes on suddenly and is usually intense but short-lived, resolving within one to three days for most people. The biggest risk is dehydration, especially in young children and older adults.
How to Tell Which One You Have
The honest answer is that respiratory viruses are hard to tell apart by symptoms alone. Fever, cough, sore throat, fatigue, and body aches show up with flu, COVID, and RSV alike. A few patterns can help narrow it down:
- Sudden onset with severe body aches leans toward flu.
- Loss of taste or smell still points more toward COVID.
- Heavy congestion with a persistent cough and no high fever is more typical of RSV in adults.
- Vomiting and diarrhea without respiratory symptoms suggest norovirus.
Home test kits can help sort things out. Rapid antigen tests for COVID pick up almost 90% of cases when you have symptoms, though they catch only about half of asymptomatic infections. Combo tests that screen for both COVID and flu in a single swab are now available, with some detecting over 90% of cases for both viruses. Testing on the first day of symptoms may produce a false negative, so retesting 24 to 48 hours later improves accuracy.
No New Mystery Illness
Despite what social media buzz might suggest, there is no unidentified new pathogen circulating in the U.S. right now. The CDC’s current outbreak list includes ongoing monitoring of measles outbreaks (which started in early 2025), a salmonella outbreak linked to backyard poultry, and the long-running COVID-19 tracking. Internationally, health agencies are watching Marburg and Ebola outbreaks in Africa and dengue globally, but none of these are causing widespread illness in the U.S.
Bird flu (H5N1) continues to circulate in wild birds, poultry, and dairy cattle, with 71 human cases reported in the U.S. since February 2024. Nearly all of those cases occurred in dairy and poultry workers with direct animal exposure. There is no sustained human-to-human transmission of H5N1 at this time.
Signs That Need Medical Attention
Most respiratory and stomach viruses run their course at home with rest and fluids. But certain symptoms signal that your body is struggling in ways that warrant a trip to urgent care or the emergency room. An oxygen level below 95% (if you have a pulse oximeter at home) is one clear threshold. A fever reaching 104°F that doesn’t respond to fever-reducing medication is another.
For stomach illnesses, the red flags center on dehydration: being unable to keep down water or medications, producing little or no urine, vomiting for more than 48 hours without improvement, or noticing blood in your vomit. A resting heart rate significantly higher than your normal baseline, especially paired with dizziness or fainting, also warrants prompt evaluation.