In August of 2020, I wrote about a CDC warning involving the potential for a spike in cases of a rare polio-like illness called acute flaccid myelitis (AFM), which has been linked to infection with enterovirus D68 (EV-D68). The enterovirus genus that EV-D68 calls home, in addition to extremely common non-polio enteroviruses like the rhinoviruses and coxsackieviruses, also contains the polioviruses and echoviruses. The 12 enterovirus species, and their over 200 known serotypes, are to blame for a wide spectrum of disease including the common cold, hand, foot, and mouth disease, pneumonia, hepatitis, gastroenteritis, pericarditis, aseptic meningitis, AFM, and classic polio. This genus of viruses, particularly the rhinoviruses (common cold), causes more human infections than any other.
The timing of the late Summer 2020 warning, and a CDC Health Alert Network advisory issued last week, isn’t a coincidence. AFM related to EV-D68, which can cause mild to severe weakness and even permanent paralysis in young children, first emerged in 2012 and, as I explained in my earlier post, has demonstrated a fairly reproducible pattern:
Cases of AFM continued to be reported after 2012, and a pattern of late summer and early fall predominance was established. A Colorado outbreak in 2014 led to the development of a national surveillance program run by the CDC and significant spikes were again seen in 2016 and 2018. The numbers have remained relatively low, but there has been a consistent increase in yearly totals with each biennial bump. There were 120, 153, and 236 proven cases in 2014, 2016, and 2018 respectively, with many more suspected but unproven cases. In the intervening years, case totals have dropped dramatically, with each having less than 50 proven cases.
In 2020, however, the pattern broke down. During that season, there were only 33 confirmed cases of AFM. The CDC was right to issue the warning, but there was already good reason to expect a low number of cases, as I explained back then:
It is possible, perhaps even likely, that we will see many fewer cases than expected if continued social distancing and the use of masks reduce the risk of spreading EV-D68.
If you guessed it had something to do with the pandemic, you were right. That respiratory virus season, at least in the amazing world of pediatric medicine, will go down as one of the most unusual that I have ever experienced. During a typical Fall and Winter, offices, urgent care facilities, emergency departments, and inpatient pediatric units are full of children with viral respiratory infections, particularly kids under the age of 2 years.
The most common culprit is usually respiratory syncitial virus (RSV, which is not mistaken for COVID-19), though there are many other viral pathogens known to cause respiratory illnesses in children. RSV alone is to blame for more than 2 million yearly outpatient visits and anywhere from 60,000 to 100,000 hospitalizations in children under the age of 5 years in the United States. And each year RSV kills a few hundred children, with premature infants and children with chronic lung or heart disease being at the highest risk of severe disease.
Non-RSV respiratory infections aren’t exactly uncommon, however. Viruses like human metapneumovirus, influenza, and parainfluenza virus types 1, 2, and 3 each put roughly 20,000 infants and toddlers in the hospital every year in the United States. Even the rhinoviruses, which are mostly associated with mild upper respiratory symptoms like a stuffy nose, can cause disease severe enough to require an admission. By the end of a three-year pediatric residency, pediatricians may have already diagnosed a thousand children with viral respiratory infections and managed more than a hundred in an inpatient setting, particularly those infected with RSV.
Though there has always been some fluctuation in how bad a particular RSV season is, as well as variation from region to region, they have always been consistently busy. Nobody has ever seen anything like what we saw in late 2020 and early 2021. At my hospital we had almost no RSV admissions and for good measure we had almost no influenza admissions. We had almost no admissions for any classic and typically common pediatric infections of any kind at all for that matter.
What was I doing in 2020? Along with many pediatric residents and hospitalists in cities hit hard by COVID-19, I could often be found helping our adult medicine colleagues, who were overwhelmed at times, by managing some younger adult inpatients with relatively mild COVID-19 infections or conditions not completely unfamiliar to a pediatrician. I truly hope to never be put in that position again.
So with so few children getting viral infections in general, thanks to the measures in place to reduce the risk of COVID-19 specifically, there were few opportunities for EV-D68 to cause AFM. And though there were some significant spikes in RSV in 2021, particularly in the South, and in the Summer oddly enough, it was another unusually mild season. During the Fall and Winter of 2021-2022, there were only 28 confirmed cases of AFM, which was consistent with typical odd numbered years since 2012.
There have only been 13 cases confirmed so far in 2022, but it’s early. And there is very good reason to expect that we will see a spike in cases this Fall that put us back on historical track, if you can call a period of only 10 years historical. The reason, essentially, is that the respiratory virus season of 2022-2023 is already hitting us hard as more and more people have returned to pre-pandemic behavior. In just the past two weeks, we have already admitted more children with viral respiratory infections than in 2020, and we will easily eclipse 2021 soon at this pace. And we are not an outlier.
Unsurprisingly, cases of EV-D68 are being reported from surveillance centers across the country per the CDC alert:
Healthcare providers and hospitals in several regions of the United States notified the Centers for Disease Control and Prevention (CDC) during August 2022 about increases in pediatric hospitalizations in patients with severe respiratory illness who also tested positive for rhinovirus (RV) and/or enterovirus (EV)…Upon further typing, some specimens have been positive for enterovirus D68 (EV-D68).
Though less than a hundred cases of EV-D68 were reported to the CDC as of August 4th, that is more than the last three years combined and is almost certainly an undercount. There are only seven regional centers that make up the surveillance network but there are reports of significant spikes in pediatric respiratory infections across the country, so it is reasonable to assume that some of these have been caused by EV-D68. We will have a much better idea how bad this AFM season is going to get by the end of September, as it takes 1-4 weeks for weakness/paralysis to develop after the initial infection.
Stay tuned. In the meantime, I’ll just point out that the same methods helpful in reducing the risk of infection with SARS-CoV-2 apply to the enterovirus genus as well as RSV and all the other potential causes of viral respiratory disease. That means good hand hygiene at all times, and masks and social distancing when prudent and possible are key to protecting children. There is no vaccine, unfortunately.