Summary: Week of 4/22/24

In great news, Biobot’s national wastewater network showed declining concentrations of SARS-CoV-2, influenza A & B, and RSV during week 16. Nationally, most major clinical metrics also declined for COVID-19 and influenza during week 15, while clinical metrics for RSV showed that the burden remains quite low. The percent of outpatient visits due to influenza-like illness (ILI) finally dropped below the national baseline of 2.9% in week 14 and has remained below the threshold in week 15, currently at 2.5%. With fluctuations in regional and national respiratory virus activity this season, wastewater data continues to prove to be useful for understanding near-real-time community health trends. Wastewater and clinical monitoring are finally showing that the end of this unusual respiratory season is coming very close to its end. 

The Bottom Line: While we are getting closer to the end of the respiratory season, we are not quite there yet. Continued wastewater monitoring is still important to keep us informed, especially when the transmission and circulation of viruses, particularly SARS-CoV-2 and influenza, are still active. If you’re feeling unwell, it’s important to minimize contact with others, consider wearing a mask in crowded spaces, and stay current with vaccinations and boosters. Taking these precautions can help keep you and your loved ones healthy.

National Outlook

RSV

National RSV wastewater concentrations continued to decrease in week 16 (through April 20th), and are currently the lowest levels we’ve observed since we began RSV testing in late October. National clinical RSV metrics continue to remain quite low during week 15.

Influenza

Influenza A and B concentrations continued to decline in week 16. Influenza A concentrations are now similar to levels we observed in late November, while influenza B concentrations are similar to those we observed in early December.  

Clinical data showed that the illness burden due to influenza continued to decline in week 15, with major metrics continuing to trend downward. The number of hospitalizations due to flu decreased, with a little over 3,800 hospitalizations occurring in week 15. Test positivity from clinical labs also continued to decrease, going from 7.7% to 5.9% currently. The percentage of outpatient visits for influenza-like illness (ILI) – typical in flu, RSV, and COVID-19 patients – continued to drop and remains below the national baseline of 2.9%, currently at 2.5%. 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 slightly declined during week 16, remaining at the lowest concentrations we’ve observed during this winter surge. As of week 16, the national SARS-CoV-2 wastewater concentration average is 255 copies/mL. 

Clinical metrics continued to show that the COVID-19 disease burden decreased nationally in week 15. COVID-19 hospitalizations dropped from around 7,300 in week 14 to around 6,400 in week 15. After many weeks of decrease, the national COVID-19 test positivity rate held steady in week 15 and is currently at 3.4%. Deaths due to COVID-19 declined in week 14 and currently represent 1% of all deaths in the US.

Regional

The South

RSV: In the South, RSV wastewater concentrations continued to decrease during week 16. Concentrations are currently the lowest values we’ve observed for the region since we began testing. 

Influenza: Influenza A and B concentrations decreased in the South during week 16, and values for both are some of the lowest we’ve observed for the region since we began testing in late October 2023. During week 15, only Oklahoma experienced an increase in outpatient visits due to ILI, with almost all other Southern states reporting decreases. In great news, all Southern states are now in the Minimal ILI activity level as of week 15. 

COVID-19: SARS-CoV-2 wastewater concentrations continued to decline in the South during week 16, currently at 167 copies/mL. The great news is that all states in the South experienced a decrease in hospitalizations due to COVID-19 in week 15. 

The Midwest

RSV: RSV wastewater concentrations decreased in the Midwest during week 16 and are currently the lowest values we’ve observed for the region since we began testing.  

Influenza: Wastewater concentrations for influenza A and B decreased in the Midwest during week 16. Concentrations for influenza A are some of the lowest we’ve observed in the region since we began testing, while influenza B concentrations remain elevated but are coming down. Most states in the Midwest experienced a decrease in outpatient visits due to IL in week 15, however, North Dakota, South Dakota, and Wiscosin experienced small increases. North Dakota is the only state in the Midwest that remains at the high ILI activity level, with all other states at the minimal or low levels. 

COVID-19: SARS-CoV-2 wastewater concentrations continued to decline in the Midwest during week 16, currently at 234 copies/mL. During week 15, most states in the Midwest experienced a decrease in COVID-19 hospitalizations, with only three (North Dakota, South Dakota, and Nebraska) experiencing increases.

The Northeast

RSV: In the Northeast, RSV wastewater concentrations continued to decline in week 16 and are currently the lowest values we observed for the region since we began testing.  

Influenza: Influenza A and B wastewater concentrations both continued to decrease in the Northeast during week 16. Concentrations for influenza A are similar to what they were in November, while concentrations for influenza B are still relatively elevated and similar to what they were in January. In good news, all states in the Northeast experienced a decrease or remained steady in the percentage of outpatient visits due to ILI in week 15. Massachusetts is the only state in the Northeast that remains at the Moderate ILI activity level, with all other states at the Minimal or Low levels. 

COVID-19: SARS-CoV-2 wastewater concentrations held steady in the Northeast during week 16, currently at 386 copies/mL. After several states in the Northeast experienced increased hospitalizations due to COVID-19 in week 14, we are relieved to report that most have reported decreases during week 15. Only Delaware and New Hampshire reported increases in hospitalizations during week 15, with all other states in the region reporting decreases.   

The West

RSV: RSV wastewater concentrations decreased in the West during week 16 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 16 and are at similar levels to those observed when we began testing in late October. Influenza B concentrations continued to decrease in week 16, and while they are still relatively elevated, they have come down to levels similar to what we observed in December. Clinical disease burden due to influenza appears to be fluctuating in the West, as more states experienced increases in outpatient visits due to ILI in week 15, including Oregon, Alaska, Hawaii, Arizona, and Wyoming. Most states in the West, however, still have relatively low influenza-like illness activity, as Wyoming is the only state in the West that remains in the High ILI activity level, while New Mexico and Alaska are the only two states in the region at the Minimal level; all other Western states fall into the Low or Minimal ILI levels. 

COVID-19: During week 16, SARS-CoV-2 wastewater concentrations slightly declined in the West, currently at 160 copies/mL. Clinical disease burden appears to fluctuate in the West as six states experienced increased hospitalizations due to COVID-19 in week 15. Western states with hospitalization increases include New Mexico, Wyoming, Montana, Arizona, Alaska, and Hawaii. 

Footnotes: 

Wastewater data from Biobot Analytics for RSV, influenza, and SARS-CoV-2 are through April 20, 2024 (MMWR week 16). 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 13, 2024 (MMWR week 15).