Summary: Week of 1/29/24

Data from Biobot’s national wastewater network and clinical disease monitoring show that activity from SARS-CoV-2 and influenza continues to decline, while RSV activity increased slightly. The trajectory for all three major respiratory viruses is still downward, indicating that we have likely made it through the peak of the respiratory virus season in the US. Despite this great news, wastewater concentrations, test positivity, and hospitalizations remain elevated for all three major respiratory viruses. 

The Bottom Line: We are still in the midst of the respiratory virus season, and the risk of exposure to the three major respiratory viruses remains elevated. Proactively taking steps to minimize your exposure and bolster your immune system can help reduce your chance of becoming ill. It is still a good idea to consider staying home when you’re not feeling well, wearing a mask in crowded spaces, and getting vaccinated.

National Outlook

RSV

Nationally, RSV wastewater concentrations increased slightly during week 4, marking an 11.2% increase in concentration. This increase is not surprising as it is quite common for RSV activity to fluctuate slightly during periods of decline – during previous RSV seasons, we’ve observed increases in hospitalizations following periods of decline. This increase does, however, signal that RSV activity is still quite elevated

In better news, as of January 20th (week 3), the percentage of PCR tests that are positive (test positivity) for RSV continued to decrease, going down from 8.4% the previous week to 7.2% currently. Hospitalization rates also continue to decrease for all age groups. We will be watching to see if clinical metrics follow wastewater and show any upticks in the coming week, but fingers crossed that they continue declining. 

Influenza

This is the fourth consecutive week that influenza wastewater concentrations decreased since the beginning of the flu season, signaling that we are likely past the seasonal peak. As of January 27th (week 4), data show that wastewater concentrations for influenza A, which is driving most transmission in the US, have decreased by 14.4%, and influenza B concentrations remained consistent. 

Clinical influenza data continue to mirror wastewater trends and show encouraging signs of a slowdown in influenza activity. The number of hospitalizations due to influenza continued to decrease in week 3, going from around 15,000 hospitalizations in week 2 to 12,382 in week 3. The percentage of hospital visits for flu-like symptoms – typical in flu, RSV, and COVID-19 patients – also continues to decrease, going from 4.7% to 4.3% in week 3. During week 3, there was a slight increase in influenza test positivity, up from 13.7% in week 2 to 14.2% in week 3. However, it’s important to interpret this metric with caution as it is more influenced by human behavior and testing patterns. Hospitalization rates, on the other hand, provide a more reliable measure of understanding the true burden of disease. Most positive flu tests continue to be influenza A, which has consistently been reflected in wastewater data. 

The good news is that decreases in wastewater concentrations and hospitalizations indicate that we have likely made it through the worst of the season. The bad news is that all these metrics remain high, meaning there is still a lot of influenza circulating and that the season isn’t over yet. 

COVID-19

Wastewater data show that COVID-19 activity and community viral load have continued to decrease throughout the previous four weeks, a strong signal that this COVID-19 wave is subsiding. As of January 27th (week 4), the national SARS-CoV-2 wastewater concentration average is 821 copies/mL. The national average concentration is following the same pattern we observed last year, with declining concentrations in January. At this time last year, wastewater concentrations were 720 copies/mL. We hope that this downward trend continues. 

COVID-19 clinical metrics continue to decrease as of January 20th (week 3). The national COVID-19 test positivity rate slightly declined again during week 3, currently at 10.8%. As we anticipated, and in great news, both hospitalizations and deaths due to COVID-19 decreased during week 3. Hospitalizations declined 14%, totaling 26,607 admissions, and deaths declined by 7.5%, now making up 3.7% of all deaths in the US, down from 4.3% the previous week. These declines in clinical metrics, corroborated by declines in wastewater, signal that COVID-19 activity continues to decline. 

Regional

The South

RSV: RSV wastewater concentrations increased in the South during week 4, signaling that RSV activity is still quite elevated in the region. Clinical data show test positivity slightly declined during week 3, going from 5.4% to 5.0%. We hope that clinical activity continues to decline in the South, but we are keeping our eye out in response to increasing wastewater concentrations.  

Influenza: In welcome news, wastewater data through week 4 show that wastewater concentrations for influenza A have begun decreasing again in the South. It appears that clinical metrics for influenza were a mixed bag during week 3 in the South. One state (Tennessee) is still in the very high category, 10 states remain in the high influenza-like illness category, and two states are now in the low or moderate category. These clinical trends were actually mirrored in the wastewater signal from week 3, where wastewater concentrations briefly stopped declining. With decreases in wastewater concentrations in week 4, we anticipate that influenza-like illness will also decline in the South soon. 

COVID-19: Wastewater concentrations continued to decrease in the South through week 4, currently at 678 copies/mL. Most states in the South saw decreases in COVID-19 hospitalization rates; however, Texas and Arkansas saw slight increases. COVID-19 metrics are mostly trending in the right direction, but activity and disease burden still remain elevated in the South. 

The Midwest

RSV: RSV wastewater concentrations slightly increased in the Midwest during week 4, suggesting that activity is still ongoing and elevated. Test positivity in the Midwest during week 3 continued to decline, dropping from 11.7% to 10.3%. This is still a high value for test positivity, and we hope that this declining trend continues.

Influenza: The Midwest experienced a slight increase in influenza A wastewater concentrations during week 4 and a steady increase in influenza B concentrations. During week 3, most states in the Midwest experienced a decrease in influenza-like illness hospitalizations, with all, except for Ohio, now in the low or moderate categories. With increases in wastewater concentrations during week 4, we are keeping an eye out for increases in clinical metrics in the following weeks. 

COVID-19: SARS-CoV-2 wastewater concentrations continued to decline slightly in the Midwest during week 4, currently at 710 copies/mL. In great news, hospitalization rates for COVID-19 declined in all Midwestern states again during week 3 as well, mirroring declines in wastewater concentration. 

The Northeast

RSV: Data through week 4 show that RSV concentrations continue to decline in the Northeast. This declining trend continued with test positivity, which went down from 6.2% to 5.5% in week 3. These consecutive declines in wastewater concentrations and test positivity signal that the Northeast has made it past its RSV seasonal peak. 

Influenza: Data through week 4 show that influenza A wastewater concentrations have declined for four consecutive weeks in the Northeast, while influenza B concentrations increased slightly. The majority of states in the Northeast are now in the moderate or low categories, with three states remaining in the high category. These trends show that influenza activity is still relatively elevated in the Northeast. 

COVID-19: SARS-CoV-2 wastewater concentrations continued to decline in the Northeast during week 4, with current concentrations at 1,140 copies/mL. In great news, all Northeastern states experienced a decrease in hospitalization rates due to COVID-19. 

The West

RSV: RSV wastewater concentrations remained consistent in the West during week 3 but remained lower than in all other regions. In good news, the decreasing trend in test positivity we observed for the previous three weeks in the West has continued, with a reduction from 7.5% to 6.5% in week 4. 

Influenza: In the West, wastewater concentrations for influenza A and B increased slightly during week 4. Clinical data through week 3 show that some regions of the West have decreasing influenza activity while others experienced slight increases. For week 3, 6 states in the West are in the low and minimal ILI activity levels, two are in the moderate levels, and 5 are in the high or very high levels. We are keeping an eye on the West and hope that clinical metrics begin decreasing across the region soon. 

COVID-19: SARS-CoV-2 wastewater concentrations slightly increased during week 4, currently at 536 copies/mL. In good news, all Western states except for New Mexico experienced a decrease in COVID-19 hospitalization rates during week 3. We hope that despite these slight increases in wastewater concentrations, hospitalizations will continue to decline in the West.

Footnotes: 

Wastewater data from Biobot Analytics for RSV, influenza, and SARS-CoV-2 are through January 27, 2024 (MMWR week 4). 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 January 20, 2023 (MMWR week 3).