Problem: Enteroviruses are common human viruses associated with various clinical syndromes, from minor febrile illness to severe, potentially fatal conditions (e.g., aseptic meningitis, paralysis, myocarditis, and neonatal enteroviral sepsis). Multiple enterovirus serotypes exist. Individual serotypes have different temporal patterns of circulation and often are associated with different clinical manifestations. Changes in circulating serotypes might be accompanied by large-scale outbreaks.

Reporting Period Covered: 1970--2005.

Description of Surveillance System: The National Enterovirus Surveillance System (NESS) is a voluntary, passive surveillance system that has monitored trends in circulating enteroviruses since 1961. Enterovirus detections by serotype with specimen type, collection date, and demographic information are reported monthly by participating laboratories to CDC, which summarizes the data and disseminates the results. For this analysis, the available data set for 1970--1982 included only information on serotype and state for each report; complete records were available for 1983--2005.

Results: During 1970--2005, a total of 52,812 enterovirus detections were reported to NESS (29,772 of them during 1983--2005). Laboratory participation and the numbers of reports declined throughout the 1990s, but they increased again after 2000. The 15 most commonly reported enteroviruses accounted for 83.5% of reports with known serotype, and the five most commonly reported serotypes (echoviruses [E] 9, 11, 30, and 6, and coxsackievirus B5) accounted for 48.1%. Predominant serotypes and ranking of individual enteroviruses changed over time. Long-term circulation patterns for individual serotypes varied but were consistent with epidemic (e.g., E9, E13, E30, and coxsackievirus B5) or endemic patterns (e.g., coxsackieviruses A9, B2, B4, and enterovirus 71). Children aged <1 year accounted for 44.2% of reports with known age. Male predominance was present among patients aged 20 years (male/female ratio: 1.4 and 0.9, respectively). Enterovirus detections had prominent summer-fall seasonality, with June--October accounting for 77.9% of reports with known month of specimen collection. Cerebrospinal fluid was the most common specimen type, followed by respiratory and fecal specimens (49.8%, 26.9%, and 13.6%, respectively). Death was reported for 3.3% of detections with known outcome. Infections with coxsackievirus B4 (odds ratio [OR] = 3.3; 95% confidence interval [CI] = 1.7--6.0), and human parechovirus 1 (formerly E22) (OR = 3.7; CI = 1.7--7.6) were associated with higher risk for death, and infections with E9 were associated with lower risk for death (OR = 0.1; CI = 0--0.4) than infections with other enteroviruses.

Interpretation: NESS data allowed identification and description of a core group of consistently circulating enteroviruses that probably determine the disease burden associated with enterovirus infections. These data also are helpful in guiding outbreak investigations and identifying targets for development of diagnostic assays and antivirals. Efforts to update the reporting system initiated in the early 2000s (i.e., simplification of reporting forms and transition to electronic reporting) resulted in a substantial increase in reporting compared with the late 1990s.

Public Health Action: Efforts to increase laboratory participation in NESS should continue to allow for more complete and accurate surveillance for enteroviruses. Further improvement in the timeliness of feedback through the development of a NESS website to allow access to historic data and to the information on circulating serotypes can provide additional incentives to public health laboratories to participate in NESS.