Abstract and Introduction
Infections caused by enteroviruses (EV) and parechoviruses (PeV), members of the Picornaviridae family, are associated with various clinical manifestations, including hand, foot, and mouth disease; respiratory illness; myocarditis; meningitis; and sepsis; and can result in death. The genus Enterovirus includes four species of enterovirus (A–D) known to infect humans, and the genus Parechovirus includes one species (A) that infects humans. These species are further divided into types, some of which are associated with specific clinical manifestations. During 2014–2016, a total of 2,967 U.S. cases of EV and PeV infections were reported to the National Enterovirus Surveillance System (NESS). The largest number of reports during that time (2,051) occurred in 2014, when a large nationwide outbreak of enterovirus D68 (EV-D68) occurred, accounting for 68% of cases reported to NESS that year. Reports to the National Respiratory and Enteric Virus Surveillance System (NREVSS) during 2014–2016 indicated that circulation of EV peaks annually in the summer and early fall. Because the predominant types of EV and PeV circulating from year to year tend to vary, tracking these trends requires consistent and complete reports from laboratories with the capacity to perform typing.
NESS is a passive, laboratory-based surveillance system that has been used to track EV and PeV reports since the 1960s and is the most comprehensive database of these reports in the United States. During 2014–2016, 11 laboratories reported to NESS, including nine state health departments, one municipal health department, and the CDC Polio and Picornavirus Laboratory Branch (PPLB). The largest contributor of reports to NESS was PPLB (1,553), which serves as a reference laboratory for jurisdictions with no or limited EV and PeV typing capacity. Testing data for untyped EV are also collected through NREVSS, a passive, laboratory-based surveillance system that collects aggregate reports of tests for EV and the percentage positive by week.
During 2014–2016, a total of 2,967 EV and PeV cases were reported to NESS, including 2,758 (93.0%) for which the type was known. Reports that included virus type represented 2,734 individual patients, among whom one virus type was identified from 2,726 (99.7%) and two types were identified from eight (0.3%). Among 2,370 (86.7%) patients with known sex, 1,422 (60.0%) were male, and among 1,351 (90.1%) for whom age was known, the median age was 4 years (interquartile range = 1–10 years). State of residence was known for 2,727 (99.7%) patients; among these, California was the most frequently reported state (413, 15.1%), followed by New York (366, 13.4%). Residents from all 50 states and the District of Columbia were represented (Figure 1). The largest number of reports to NESS that included EV and PeV type (2,051) occurred in 2014 (Box); these reports accounted for 74% of the 2,758 reports for all 3 years.
States from which enterovirus-positive or parechovirus-positive results were reported, by Surveillance system — United States, 2014–2016
Abbreviations: DC = District of Columbia; NESS = National Enterovirus Surveillance System; NREVSS = National Respiratory and Enteric Virus Surveillance System; PR = Puerto Rico.
EV-D68 was the most frequently reported type during 2014–2016, accounting for 1,542 (55.9%) reports for this period, including 1,395 (68.0%) in 2014, when a large nationwide outbreak of respiratory disease associated with EV-D68 occurred. In 2015, EV-D68 accounted for only nine (2.4%) reports that included virus type. EV-D68 again constituted a large percentage (40.9%) of reported types in 2016, but the 138 reports represented <10% of the EV-D68 reports in 2014. Overall, 1,351 (86.7%) EV-D68 detections were from respiratory specimens; 154 (9.9%) were from specimens whose source was unknown.
After EV-D68, the most frequently reported types during 2014–2016 were echovirus 30 (159; 13.1% of 1,216 reports of non–EV-D68 types), coxsackievirus (CV)-A6 (152; 12.5%), echovirus 18 (116; 9.5%), and CV-B3 (109; 9.0%). Among reports in which a type other than EV-D68 was detected (1,466), the most frequently reported specimen source was cerebrospinal fluid (493; 38.0% of 1,298 specimens with known source), followed by throat/nasopharyngeal swab (487; 37.5%).
Data reported to NREVSS were used to evaluate trends in the percentage of tests positive for EV over time. Among 62,210 specimens from which virus isolation was attempted in 47 laboratories, 0.6% (347) tested positive for untyped EV; among 70,915 specimens tested in 72 laboratories by reverse transcription–polymerase chain reaction, 5,555 (7.8%) tested positive. The percentage of specimens testing positive peaked in summer or early fall for all years (Figure 2). The decline in the percentage of positive results during July and August 2014 was associated with a substantial increase in the number of EV tests performed during the EV-D68 outbreak period.
Morbidity and Mortality Weekly Report. 2018;67(18):515-518. © 2018 Centers for Disease Control and Prevention (CDC)