Outbreak Outlook - National - March 1
Flu plateau, RSV hospitalizations rise, Covid low
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Influenza-like illness
New month, same flu. Despite some slight decreases, we are still stuck on a plateau stretching back to mid-January. Outpatient visits are holding steady at 4.4%, and about half of the states continue to report high or very high activity. It’s not uncommon for the season to run this long, but it does feel unfortunate given how high this season’s January peak was.
There were slight decreases in outpatient ILI for each age group. (Looking hard for a silver lining here.) The youngest kids continue to head to the doctor the most often for flu-like illness: 11.7% of those aged 0-4. For those 5-24, outpatient visits for fever and cough or sore throat were at 8.4%, and were <4% for all other groups.
Emergency department (ED) visits decreased slightly to 3.2% nationally from 3.5% the week prior. ED visits are about the same in the Midwest, West, and South at a little over 3%. The Northeast is doing a bit better, and ED visits there have declined to around 2%. Hospitalizations are still elevated at 3.0 hospitalizations per 100,000, but are slowly declining.
Flu B continues to account for a greater proportion of cases, and now accounts for a majority (55.1%) of clinical lab samples, and nearly a third (28.9%) of public health lab samples. Flu B often ramps up in the springtime, after flu A has faded.
Regional editions are wrapping up for the season soon (more info on that to come). Paid subscribers will continue receiving the summer report, which contains updates on Covid-19, norovirus, food recalls, and more throughout the off-season. Free subscribers get occasional posts, with the free national edition returning next October when flu season resumes.
COVID-19
Covid-19 activity remains fairly low nationally. ED visits held stable at 0.6% this past week. Wastewater activity has been moderate for the past couple months nationally.
The Midwest continues to see higher activity than anywhere else, but even there activity is declining. ED visits have declined to a little under 1% for the region. Both the Northeast and South have ED visits ~0.7%. The West is doing particularly well, with ED visits down to ~0.4%. More severe illness, i.e., hospitalizations, are also holding steady at a fairly low 1.4 hospitalizations per 100,000. All told, activity is fine but not fantastic.
RSV & Other Bugs
RSV: Activity continues to be fairly high and rising. ED visits for RSV held steady at 0.6%. RSV test positivity is still going up, now at 8.6%. This is higher than it has been all season, but still a bit below last year’s peak. Hospitalizations continue to rise, reaching 3.2 hospitalizations per 100,000 this past week.
Activity is slightly higher in the West and Midwest, where ED visits are around 0.7%. Hospitalizations, however, are highest in the Northeast, at about 3.4. Things are improving a bit in the South, which has the lowest ED visit rate and hospitalizations decreased this past week to under 2.0 hospitalizations per 100,000 people.
Other bugs:
These are less-common causes of cold- and flu- symptoms. Surveillance for these pathogens is not very comprehensive, so we have only broad trends to analyze.
If you have a cold right now, you may very well have a human coronavirus to blame. Activity is very high and peaking.
Human metapneumovirus is also spiking.
Adenovirus has dropped to moderate levels
Parainfluenza and rhinoviruses/enteroviruses are very low right now.
Norovirus
Norovirus activity is very high. This is about the time of year when I expect rates to slowly start declining, and we did see a slight dip this past week in test positivity, to 14% nationally.
Hang in there!
Food recalls
The following foods are being recalled because they are contaminated. Please check your cupboards and throw out any of these items:
New:
Great Value (sold at Walmart) Cottage Cheese (more info)
Elite Treats Chicken Chips (for dogs). These may be contaminated with salmonella, which poses a health risk not only for dogs, but also for humans who handle the product or contaminated surfaces (more info).
Bremer Family Size Italian Meatballs (frozen, ready-to-eat) (more info)
Previously Reported:
Multiple flavors of cream cheese under the Made Fresh Salads, Inc. label (more info)
Frozen chicken fried rice products, sold under Trader Joe’s and Ajinomoto labels due to possible glass shards (more info)
Gerber Arrowroot biscuits (more info)
Organic chia seeds sold by Navitas Organics (more info)
In other news
ByHeart Infant formula botulism outbreak declared over. The CDC has closed the investigation into the ByHeart infant formula, which resulted in 48 confirmed and probable cases across 17 states, all 48 of which involved hospitalizations. Fortunately, no deaths were reported in this outbreak. Infants were sickened between December 2023 and November 2025. I find it troubling that the outbreak went on for so long, unrecognized. The FDA’s investigation into what caused the outbreak is ongoing.
Measles outbreak grows. In just eight weeks, the country has already recorded nearly half as many cases as all of last year, according to CDC data (1,136 so far this year compared to 2,281 in 2025). Cases have been reported in 28 states so far this year, and 90% of these are outbreak-associated (that is, the vast majority of cases are acquired via domestic, community spread). The most affected states so far this year are South Carolina (653), Florida (107), and Utah (149).
Reportable disease reports. If you are curious about FOI Clinical, a deep dive on seasonal vaccine effectiveness for the 2025-2026 season is now free to read. FOI Clinical is an outbreak report for clinicians (though all are welcome), with a focus on reportable diseases. Recent coverage has included measles, mumps, chicken pox, tularemia, mpox, and more. Subscribers also get real-time health alerts, recently on extensively drug resistant salmonella and flu B; 96% of readers have found the content helpful.
Thanks for the data. Much appreciated.
Wondering if the increased percent of RSV visits has to do with a slight dip in protection from the monoclonal antibodies that were administered early in the season? Or is it just that other illnesses have decreased relative to rsv?