Respiratory Diseases

Influenza-like illness

Flu season is officially here. 3.2% of outpatient visits were for influenza-like illness, above the baseline for the start of flu season. Test positivity has increased to 8.1%, up from 2.9% one month ago. Wastewater activity is low but increasing.

While most states continue to have minimal or low activity, there are now 9 states where activity is moderate or higher. Hotspots are New York, New Jersey, Colorado, and Louisiana.

Outpatient ILI increased slightly for the youngest age group (0 to 4 years of age) to 9.5%. It held steady for those 5-24, at 5.3%, and for those 65 and older at 1.3%. It also increased for those aged 25-49 (to 2.7%) and 50-64 (to 1.9%).

Since activity in kids hardly grew at all, does that mean flu season is slowing down? No, I don’t think so. Most growth is driven by infections in children, who get sick more often because of mixing in schools and childcare. This week, pediatric flu growth dropped off, pulling down the overall numbers.

My hypothesis is that because kids were out of school during the week of Thanksgiving, they were less exposed than usual. Given the incubation period, we’d expect this reduction to appear in the data during this reporting week (which covers the week ending December 6), which is exactly what happened. I checked the data from 2023 and 2024 and the same dip occurred at this time both years. Activity rebounds in the following weeks, so I expect the same pattern now.

A large majority (86% of samples tested) are H3N2. The European CDC reports that H3N2 has been linked to an early flu season (we haven’t seen that in the U.S.) and may cause peak activity to be on the high side. However, there is currently no evidence that H3N2 causes more severe disease. The report I reviewed from WHO says similar.

COVID-19

Covid-19 remains low, but I think we’ve passed the lowest point and are beginning a new ascent. While not welcome, that’s typical for wintertime, and we have enjoyed an unusual period of quiet these last months.

Wastewater activity increased from very low to low levels nationally. Activity is highest in the Northeast, where activity has increased sharply to moderate levels. Activity low and increasing in the Midwest, and very low and increasing in the South. It remains low and stable in the West.

Severe illness remains very low. ED visits increased slightly to 0.4% nationally. Hospitalizations also increased slightly, to 1.2 hospitalizations per 100,000 people.

RSV & Other Bugs

RSV: RSV is still pretty low, but it is growing in most states in the country.

• Wastewater activity is very low or low in most states. However, rates are moderate in Washington, DC and Florida, high in Kentucky, and very high in Colorado and Louisiana.

• ED visits are at 0.3%, which is about half of where they were this time last year. Even for the youngest children — who tend to be most impacted by RSV — ED visits are very low compared to last year (2.8% vs 6.5%). Similarly, test positivity is at 2.9%, compared to 8.4% this time last year.

• Hospitalizations have increased slightly to 0.8 hospitalizations per 100,000 people.

Other bugs:

• Adenovirus and parainfluenza appear to have passed their peaks, but are both still very active.
• Rhinoviruses/enteroviruses continue to fall down, after peaking in September, but remain at fairly moderate levels.
• Human coronaviruses and human metapneumovirus are low, but rising.

Norovirus

Norovirus is moderate, decreasing a bit this past week nationally to 9.4% test positivity. While I appreciate the drop, I would not take this as a sign that the worst of the season has passed (except maybe in the South). This is because norovirus test positivity tends to be quite jagged (moving up and down from week-to-week), and because it tends to be very active in late winter.

Activity has fallen sharply in the South over the past few weeks, down to 10.7% from 18.9% in mid-November.

In the Midwest, test positivity dipped slightly to 9.9%, and in the West, test positivity has decreased to 8.9%. In the Northeast, test positivity decreased to 4.9%

Food recalls

The following foods are being recalled because they are contaminated. Please check your cupboards and throw out any of these items:

New:

• Town Food Service Equipment Co. Aluminum Saucepans, due to potential lead contamination (more info)
• Lucky Foods cinnamon powder, due to potential lead contamination (more info)

Previously Reported:

• Wegmans Deluxe Mixed Nuts Unsalted (more info)
• Grated Pecorino Romano cheese, sold under various labels, including Boar’s Head, Locatelli, Member’s Mark, Ambriola, and Pinna at major retailers, including Wegman’s (more info)
• Prairie Farms Gallon Fat Free Milk (more info)
• ByHeart Infant Formula due to potential botulism contamination (more info)

In other news

• Last-minute holiday gifts.

  • Hardcover copies of Crisis Averted are still selling for less than $10 on Amazon. If you want a preview before deciding, check out this excerpt I adapted for the New York Times (gift link).

  • You can also gift this newsletter to others!

• The infant botulism outbreak linked to ByHeart formula continues to grow. There have been 12 new cases and hospitalizations reported, bringing the total to 51 cases and hospitalizations among infants. Fortunately, no deaths have been reported in this outbreak. Infants have been affected in 19 states. Most of these cases are not new-onset however. They occurred from December 2023 through July 2025 and are now being linked to this outbreak. It is very concerning that contaminated infant formula has been circulating for potentially years before being identified. All ByHeart products have been recalled, and caregivers are urged to stop using any and all products by the company.

• Measles cases are rising. According to the CDC, as of December 9, there were 1,912 confirmed measles cases in the US so far this year. The vast majority of these cases were from domestic spread in the United States (rather than cases in international travelers). More than 1 in 10 people infected have been hospitalized this year, with 21% of all children under the age of 5 who were infected needing to be hospitalized. The hotspots right now are in Utah-Arizona and in South Carolina. In South Carolina, 27 new cases were reported in the last week (114 in the state since the summer). There have been 26 new cases in the past three weeks in Utah (115 this year), and 17 new cases in the past week (175 this year) in Arizona.

• Origin of African swine fever outbreak in Spain under investigation. African swine fever was identified several weeks ago in wild boars in the Catalonia region of Spain. Swine fever (which does not affect humans) can cause significant losses for pork producers, and an outbreak among wild boards can spread to domestic pigs. Investigations into the outbreak are ongoing, and some early evidence has found that the strain of the virus spreading among the wild boar has similarities to a strain frequently used in research, and, at the same time, is not particularly similar to other strains spreading in Europe right now. This suggests that the outbreak may have originated from an accidental laboratory release, though additional research is needed before any conclusions can be drawn. The regional government has requested an audit of a research institute with facilities near the outbreak site that work with the virus.

• Multistate equine herpesvirus. There have been 60 equine herpesvirus cases confirmed across 8 states since the beginning of November. This is the first multistate outbreak of the disease in the US in over a decade. A special network to share information among owners and veterinarians, the Equine Disease Communication Center, has been credited with helping to rapidly share information about the outbreak and limit spread. Equine herpesvirus can cause severe illness in horses (the disease does not spread to humans). Numerous cases have been linked to a rodeo event in Waco, Texas from Nov 5-9; however, a few of the reported cases are not associated with the event.

• Highly pathogenic avian influenza is spreading across poultry farms. In the past month, more than 1 million birds have been affected, across 7 states: Indiana, North Dakota, South Dakota, Minnesota, Iowa, Michigan, and North Carolina. HPAI tends to increase over the fall and winter, as migrating birds transmit the virus to commercial flocks. HPAI spread among commercial flocks has economic consequences, and poses an ongoing risk of mutation and spillover to humans.

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