Summary: Week of 5/6/24

We want to share the information that we have at the moment on the rapidly evolving H5N1 influenza virus situation. Biobot’s influenza A assay detects the H5N1 influenza subtype, which is an influenza A virus, but does not distinguish between the different subtypes of influenza A (e.g., H5N1 vs. H1N1). While we are not seeing a widespread increase across the country in influenza A virus in the recent week, we are seeing a slight uptick in influenza A concentrations in the Midwest. The uptick in the South during week 17, which we reported on last week, has thankfully gone back down. We want to highlight some important points about the role of Biobot’s wastewater data in understanding the current circulation/risk of H5N1 in the South and nationally: 

• At this point, we cannot determine if these upticks are due to seasonal influenza A virus or if H5N1 could be playing a role in the increase. 
• Biobot is currently testing for influenza A in 7 out of the 9 states with positive dairy herds (Texas, New Mexico, Kansas, Idaho, Ohio, North Carolina, and South Dakota), among several other states across the country. 
• Our current assays do not distinguish between infections in humans versus infected animals that are shedding into the wastewater system. 

This situation is rapidly evolving and our team will continue to closely monitor H5N1. We will provide any additional information as it becomes relevant or available via Twitter and here in the risk reports.

Biobot’s national wastewater network showed declining national concentrations of SARS-CoV-2 and influenza A & B during week 18, while RSV concentrations slightly increased, mostly driven by an uptick in the Midwest. Nationally, all major clinical metrics also declined or held steady for COVID-19 and influenza during week 17, and clinical metrics for RSV continue to show that illness burden is quite low. The percentage of outpatient visits due to influenza-like illness (ILI) continues to stay below the national baseline of 2.9%, currently at 2.2%. Overall, the illness burden due to respiratory viruses is currently low. 

We are continuing to pay close attention to the evolving H5N1 situation. While influenza A concentrations have gone back down in the South through week 18, which is welcome news, we have observed a slight increase in concentrations in the Midwest. It is imperative that we continue to pay close attention to any fluctuations in wastewater and clinical data and take note of any trend changes. Wastewater data will be particularly important to understanding community viral activity moving forward, as national requirements for reporting hospitalizations due to COVID-19 and influenza ended on May 1st, 2024. 

The Bottom Line: As we address the evolving H5N1 situation, leveraging every public health tool, including wastewater monitoring, is crucial for staying ahead of potential public health threats. It is important to understand that, currently, H5N1 does not pose a significant risk to human health. However, closely monitoring this situation is essential. Our recommendations to keep yourself and loved ones healthy remain the same: if you feel unwell, minimize contact with others, consider wearing a mask in crowded areas, and stay current with vaccinations and boosters. Taking these precautions can help keep you and your loved ones healthy.

National Outlook

RSV

Surprisingly, national RSV wastewater concentrations slightly increased in week 18 (through May 4th). It appears that most of this national increase is driven by an uptick in the Midwest. In good news, though, national clinical RSV metrics continued to decline in week 17 and remain low. While we’ll keep an eye on RSV, we think these small fluctuations will likely fizzle out.

Influenza

Nationally, influenza A & B concentrations decreased in week 18 and remain low. We continue to keep a close eye on influenza A concentrations as the highly pathogenic avian influenza virus (HPAI) H5N1 is an influenza A virus subtype that our assay picks up. Right now, we don’t see any national increases in influenza A, which is great news. 

Clinical data showed that the illness burden due to influenza continued to decline in week 17, with major metrics continuing to trend downward. The number of hospitalizations due to flu decreased, with a little over 2,300 hospitalizations occurring in week 17. Test positivity from clinical labs also decreased, going from 4.8% to 3.9%. The percentage of outpatient visits for influenza-like illness (ILI) – typical in flu, RSV, and COVID-19 patients – held steady in week 17 and remains below the national baseline of 2.9%, currently at 2.2%. The national baseline is determined by examining influenza-like illness outpatient visits during non-influenza weeks (roughly late spring to late summer when influenza transmission is very low) for the previous two years.

COVID-19

Wastewater data show that COVID-19 activity and community viral load held steady during week 18 and remain close to the lowest concentrations we’ve observed during this winter’s surge. As of week 18, the national SARS-CoV-2 wastewater concentration average is 210 copies/mL. 

Clinical metrics continued to show that COVID-19 disease burden decreased nationally in week 17. COVID-19 hospitalizations dropped from around 5,600 in week 16 to around 5,100 in week 17. Test positivity slightly held steady in week 17, currently at 3%. Deaths due to COVID-19 also held steady and currently represent 0.8% of all deaths in the US. 

Regional

The South

RSV: In the South, RSV wastewater concentrations remained very low during week 18. These concentrations indicate that RSV activity in the South is currently minimal.  

Influenza: Continuing recent trends, influenza B concentrations decreased in the South during week 18. After an uptick in influenza A concentrations in week 17, we are relieved that concentrations have come back down in week 18. We are paying close attention to what’s happening in the South right now in light of the evolving H5N1 avian influenza situation. Last week’s post mentioned that our influenza A assay detects H5N1. However, it does not provide the information needed to distinguish between influenza A subtypes, for example, H5N1 versus H1N1. In good news, clinical data continues to show good signs of low disease burden – most states in the South either held steady or experienced decreases in outpatient visits due to ILI during week 17. The exception was South Carolina, which experienced a small increase in ILI activity. All Southern states remain at the Minimal ILI activity level. We will keep a close eye on this evolving situation, continue working with local public health authorities across the country, and provide updates as we obtain more information. 

COVID-19: SARS-CoV-2 wastewater concentrations held steady in the South during week 18, currently at 124 copies/mL. Most states in the South experienced a decrease in hospitalizations due to COVID-19 in week 17, with the exceptions of Florida and Kentucky, which experienced small increases.

The Midwest

RSV: Somewhat unexpectedly, RSV wastewater concentrations increased in the Midwest during week 18. It also appears that test positivity began to slow down its decline in the Midwest recently but did decline in week 17. Concentrations and test positivity remain relatively low for the region, but we will keep an eye on both.   

Influenza: Influenza B wastewater concentrations held steady and remained low in the Midwest during week 18. Wastewater concentrations for influenza A, however, slightly increased in the Midwest. As stated before, we are paying close attention to influenza A metrics in light of the evolving H5N1 situation. Of note, Kansas, Michigan, Idaho, Ohio, and South Dakota are all Midwest states that have reported cattle herds positive for H5N1. Biobot currently samples and tests for influenza A in all of these states except Michigan. It is important to understand that while we are seeing a slight uptick, influenza A levels in the Midwest remain relatively low for the region, indicating that influenza A circulation is not widespread. Moreover, clinical data shows good signs of decreasing illness burden due to influenza. Most states in the Midwest experienced a decrease in outpatient visits due to IL in week 17, with exceptions including Minnesota and Wisconsin, which experienced small increases. Additionally, all states in the Midwest have Low or Minimal ILI activity levels.  

COVID-19: SARS-CoV-2 wastewater concentrations held steady in the Midwest during week 18, currently at 201 copies/mL. During week 17, most states in the Midwest experienced a decrease in COVID-19 hospitalizations or held steady, with only North Dakota experiencing an increase. 

The Northeast

RSV: In the Northeast, RSV wastewater concentrations continued to decline in week 18 and are currently the lowest values we observed for the region since we began testing.  

Influenza: Influenza A and B wastewater concentrations decreased in the Northeast during week 18. Concentrations for influenza A are similar to what they were in early November, and concentrations for influenza B are similar to those in early December. All states in the Northeast either held steady or experienced a decrease in the percentage of outpatient visits due to ILI in week 17. All Northeastern states remained in the Low or Minimal ILI activity levels. 

COVID-19: SARS-CoV-2 wastewater concentrations slightly increased in the Northeast during week 18, currently at 318 copies/mL. Almost all states in the Northeast experienced decreases in hospitalizations due to COVID-19 in week 17, with the exceptions of New Hampshire and New Jersey, which experienced slight increases.

The West

RSV: RSV wastewater concentrations remained low in the West during week 18 and are currently the lowest values we’ve observed for the region since we began testing.  

Influenza: Wastewater concentrations for influenza A remained stable and very low in the West during week 18 and are at similar levels to those observed when we began testing in late October. After a brief increase in week 17, influenza B concentrations began decreasing again in the West during week 18.  Clinical metrics continue to fluctuate in the region but remain low overall. During week 17, most states held steady or experienced decreased outpatient visits due to ILI, except Arizona, Nevada, Montana, and Alaska, which experienced increases. In good news, though, all Western states remain in the Low or Minimal ILI activity levels. 

COVID-19: During week 18, SARS-CoV-2 wastewater concentrations held steady in the West, currently at 154 copies/mL. Similar to influenza activity, the West continues to experience more fluctuations than other regions when it comes to clinical metrics. Most states reported decreases in hospitalizations due to COVID-19 in week 17, except New Mexico, Idaho, Nevada, Colorado, and Alaska. Despite these fluctuations, the clinical burden due to COVID-19 remains low in the West.

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Footnotes: 

Wastewater data from Biobot Analytics for RSV, influenza, and SARS-CoV-2 are through May 4, 2024 (MMWR week 18). Clinical data on testing, hospitalizations, and emergency department visits for RSV, influenza, and COVID-19 are from the Centers for Disease Control and Prevention. Updates to clinical data for RSV, influenza, and COVID-19 are through April 27, 2024 (MMWR week 17).