Outbreak Outlook - National - April 22
Plus the latest on H5N1
ILI
Seasonal: Influenza-like illness (ILI) is at 2.3%, well below the national baseline of 2.9% which marks the beginning and end of flu season. No jurisdictions are in the very high or high categories; only one (North Dakota) is moderate. All other states are low or minimal.
On H5N1: The same surveillance systems used to track “regular” flu are also used to monitor for the emergence of a possible pandemic influenza — like H5N1. So the continued decline in influenza-like illness, both in outpatient and emergency data streams, is useful reassurance that H5N1 is not circulating widely in humans.
Moreover, as part of our country’s influenza surveillance, a selection of influenza specimens are sent for additional testing to see what type of influenza it is (e.g., H1N1, H3N2). In the most recent week, for example, 63 specimens were typed. This is one of the ways that H5N1 would be detected.
The other, more likely way is if someone is ill and undergoes diagnostic testing. Most standard diagnostic tests in the hospital or clinic cannot directly confirm an H5 infection. However, they can determine that a person has an influenza A virus that is not type H1 or H3. This result should prompt a clinician to send the sample for further testing to pinpoint the specific type of influenza.
COVID-19
Covid-19 activity is low. The rate of new weekly hospitalizations is still declining, and wastewater concentration is low.
There are a few little hints that have me paying closer attention. First, the variant KP.2, jumped from an estimated 10% of 25% of variants circulating (these estimates are uncertain) in the U.S. Scientists have found that it likely has an advantage over the currently-dominant variants. And the United Kingdom is seeing a small increase in Covid-19 metrics like test positivity, particularly in the oldest age groups. At this point I’m not especially worried that this variant will give us an early summer wave, but I’m keeping an eye on the data just in case.
Stomach Bugs
This has been a loooong norovirus season, and test positivity is still high. I’m ready for it to end!
Food recalls
The following foods are being recalled because they are contaminated. Please check your cupboards and throw out any of these items:
New
None
Previously reported:
Fresh basil sold at Trader Joe’s (more info)
Helados Mexico mango bars (more info)
Trader Joe’s 50% Less Salt Roasted & Salted Whole Cashews (more info)
If you have food allergies, you may wish to review these FDA safety alerts and USDA alerts for foods with undeclared allergens.
In other news
Avian influenza A(H5N1) continues to draw my attention. The virus has now been reported in 34 herds of dairy cattle across 9 states. A federal order requiring testing of lactating cows being moved between states takes effect today, which I expect will increase the number of reported cases.
It was reported last week that viral RNA was found in some 20-40% of commercial milk samples sourced from multiple states. Tests confirmed that the virus had been inactivated by pasteurization, meaning it cannot cause infection. The finding suggests significant underascertainment (meaning there are more out there we haven’t found).
One of the themes of my career is that rapid, transparent data sharing is absolutely essential to effective outbreak response. We haven’t seen that, yet. CDC has been ramping up information sharing, but data coming out of USDA has been thin. Some genomic data was released recently, but it didn’t have metadata like where or when the samples were collected. No data about how many tests are being run has been shared, either. I would like to see more data sharing in the week ahead so the scientific community can make a better assessment of where things stand, to supplement the work being done in government.
Now, on to mpox. According to the Associated Press, “Republic of the Congo has declared an epidemic of mpox after 19 cases were confirmed across five departments, including the capital Brazzaville.” The first cases in the country were reported last month. Neighboring Democratic Republic of Congo has been grappling with the virus for some time now.
The current outbreak is presumed to be clade I, which is different from the clade IIb outbreak implicated in the 2022 epidemic.
Epidemiologists in the neighboring Democratic Republic of Congo have found evidence that the virus is spreading through heterosexual contact. There is also a large number of cases in children, which could suggest household transmission. Both of these characteristics are new compared to the 2022 event, and raise concerns about wider spread.
I would caution that to describe HPAI H5N1 as "pandemic influenza" is very inappropriate. You wrote:
"...The same surveillance systems used to track “regular” flu are also used to monitor
for the emergence of pandemic influenza — like H5N1. ..."
H5N1 is currently an avian influenza that has demonstrated enormous virulence as an epizootic (all avian species), and with a disturbingly high case fatality rate where it has infected roughly 860 humans (since 1997), but it has NOT yet evolved to be capable of sustained person-to-person spread in a quarter-century, largely because of the Sialic acid receptor incompatibility in the human upper respiratory epithelium.
Have you heard about IAV in bats? Just posted it today. Another potential spillover and quite interesting. I do think we are better prepared for H5N1 and its Reassortment.