A new CDC analysis concludes that “the number of children hospitalized for hepatitis of unknown cause *has not increased* compared to before the COVID-19 pandemic.” (Emphasis in the original.)
Great–but this study is full of important limitations. The real takeaway here is “We couldn’t find any difference, but that could have been because of data limitations.”
What you need to know: this study isn’t the conclusion, it’s just a chapter in an ongoing story.
A new CDC analysis compared the number of acute hepatitis cases among children in recent months (during a widely reported public health advisory) to the same calendar months in years before the pandemic. The researchers also looked at the rates of liver transplant and adenovirus types 40/41. They found NO increases in acute hepatitis (liver failure) of unknown cause, liver transplant, or adenovirus types 40/41. However, before we run away with any conclusions about the hepatitis outbreak, we need to take a closer look at the limitations of this study.
1️⃣ Hepatitis of unknown cause is not “reportable” in the United States. That means that when someone gets acute liver failure, the case does not have to be reported to the CDC for tracking purposes. In other words, we don’t really know the baseline levels of this problem in kids. Similarly, we do not routinely test for adenovirus, so we have no idea what the “normal” incidence of adenovirus types 40/41 might be.
2️⃣ Person-to-person infectious diseases of many types were less common during the pandemic. We’ve seen several typical kid viruses that have been playing “catch-up” as our social interactions have normalized. For example, we had a very unusual summer outbreak of RSV in 2021, and this year many parents can attest that colds seem more common than ever. We wrote a post about this not long ago.
It’s possible that some or all of the recent hepatitis cases do have an infectious disease as their cause, and that disease is playing catch-up like many others.
3️⃣ Acute hepatitis in children is very rare–both now and in previous years. Therefore, a change of just 1 or 2 cases could be important, but also hard to measure. The results here could easily be due to problems with the data (see limitation #1), or just chance. The study authors say that “small changes in incidence might be difficult to detect and interpret.”
4️⃣ Finally, this analysis was at the national level. Cases of acute hepatitis during the recent public health advisory were observed in geographic clusters. They were not distributed all around the United States. Clustering like this *does* suggest some local cause, such as an infectious disease outbreak or a toxic exposure. A national-level analysis doesn’t seem super useful for the purposes of ruling out infectious causes.
That said, this study is still helpful in its own ways. Though it doesn’t rule *out* infectious causes, it does help establish how common acute hepatitis is in kids, which helps us benchmark what might be unusual. It also really highlights the need for great surveillance data! The more we know, the better off we are in terms of public health.