Data Snapshot: US Covid-19 wastewater levels today versus 1 year ago.

Things are much better than they were, but the new Omicron XBB subvariant could change that.

Weekly coronavirus levels detected in wastewater. These levels are averages and therefore the addition of new detection sites over time adds accuracy, but not magnitude. Therefore, it’s reasonable to compare these numbers over time. Source: Biobot. Image: Benjy Renton for Inside Medicine.

Official Covid-19 case counts can be unreliable these days. Some places test more than others. Also, at-home test results don’t get reported to public health officials much of the time. That’s why tracking the amount of SARS-CoV-2 virus in wastewater is so powerful. Increasingly, public health officials and epidemiologists look to wastewater, not official case counts, to get a sense of where things stand on the Covid-19 front.

So where are we now and how does that compare to a year ago?

One year ago, the Omicron variant of SARS-CoV-2 was tearing its way across the United States, leading to an overwhelmed healthcare system. Today, with new Omicron subvariants and the winter holidays upon us, a somewhat predictable increase in Covid-19 has occurred in the last few weeks.

In particular, the XBB Omicron subvariant now comprises a majority of new cases in various parts of the Northeast, coinciding with an overall rise in Covid-19 there. The Northeast is the only region of the country whose current Covid-19 wastewater levels are higher than they were this spring and summer. If this new subvariant spreads elsewhere, it would not be surprising if similarly fast increases in the disease followed suit.

Nevertheless, it’s worth noting that compared to a year ago, SARS-CoV-2 wastewater levels—an excellent proxy for Covid-19 case counts—are markedly lower now. For the nation as a whole, levels are around 1/3 of what they were last year at this time. Of course, we don’t know how things will change coming out of the holidays, especially as people are less likely to take precautions (like masking and testing) that decrease the spread of the virus than they were in the last two winters of the pandemic.

Coronavirus wastewater levels in the week leading up to Christmas 2021 versus 2022. Source: Biobot. Image: Benjy Renton for Inside Medicine.

Hospitals are also now facing an unfamiliar situation: Covid, influenza, RSV, and the usual mix of patients who are sick for other reasons. Add an exhausted (and likely smaller) healthcare workforce, and the next couple of months could be challenging times for hospitals and patients.

We’ll keep tabs on these numbers. If things skyrocket, we’ll update this post.

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Special thanks for Benjy Renton for curating Data Snapshot.