Tracking Enteroviruses and Parechoviruses in the U.S., 2014–2016

Enteroviruses (EV) and parechoviruses (PeV), members of the picornavirus family, cause a wide range of illnesses — hand, foot and mouth disease, respiratory illness, myocarditis, meningitis and sepsis — and can kill. Four enterovirus species (A–D) and one parechovirus species (A) infect people, and each is divided into types, some tied to particular illnesses. Because the dominant types shift from year to year, tracking them depends on steady reports from labs that can type the viruses. Glen R. Abedi and colleagues at CDC summarized U.S. data for 2014–2016.

Two surveillance systems

What NESS recorded

• 2,967 cases in 2014–2016, 2,051 of them in 2014.
• The type was known for 2,758 (93.0%). Among patients with typed reports, one type was found in 99.7% and two in 0.3%.
• 60.0% of patients with known sex were male; the median age was 4 years.
• Patients came from all 50 states and D.C., most often California (15.1%) and New York (13.4%).

The EV-D68 outbreak

Enterovirus D68 (EV-D68) was the most reported type, 1,542 reports (55.9%), dominated by a large nationwide outbreak of respiratory illness in 2014, when it made up 68.0% of typed reports. In 2015 it almost vanished — 9 reports (2.4%) — then returned in 2016 at 40.9% of typed reports, though with 138 reports, fewer than a tenth of 2014's. Most EV-D68 detections came from respiratory samples.

The 2014 outbreak spurred a surge in testing: typed reports that year were about three times the 594 of 2012, the busiest year of 2009–2013. A CDC-developed rapid PCR test for EV-D68 was widely adopted by public health labs that year.

Other common types

For types other than EV-D68, samples came most often from cerebrospinal fluid (38.0%) and throat or nose swabs (37.5%).

Reported enterovirus and parechovirus types, 2014–2016. Credit: CDC, MMWR.

A summer virus

NREVSS data showed enterovirus positivity peaking every summer or early fall. Of 62,210 samples tested by virus culture in 47 labs, 0.6% were positive; of 70,915 tested by PCR in 72 labs, 7.8% were.

Why type-based surveillance matters

Typing helps public health workers learn each type's long-term patterns, link illness trends to circulating types, spot outbreaks, guide new tests and treatments, and watch for poliovirus, which is nationally notifiable. Recent outbreaks — EV-D68 respiratory illness, severe hand, foot and mouth disease from coxsackievirus A6, and a cluster of severe parechovirus A3 infections in infants — show why.

But fewer labs type these viruses now. Fast molecular "pan-enterovirus" tests have largely replaced cell culture in clinics, and they don't identify the type. Parechovirus testing is less common still, and typing is mostly left to reference labs.

Limitations: NESS is voluntary and, apart from polio, these infections aren't nationally notifiable; it collects no clinical details, so types can't be linked to illness severity; typing happens mostly in summer; and reports often arrive late. Better surveillance would need more labs with modern typing capacity reporting on time.

Sources

Based on Abedi GR, Watson JT, Nix WA, Oberste MS, Gerber SI, "Enterovirus and Parechovirus Surveillance — United States, 2014–2016," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.