An outbreak of echovirus 33 in schools in China in 2013

Echovirus 33 (E33) has been infrequently detected and is less frequently associated with clinical diseases when compared with other types of enteroviruses (EVs) in China. An outbreak of E33 was identified in four schools in Hunan Province, China, in June 2013. For laboratory diagnosis, throat swabs and/or serum specimens were collected from 27 patients. E33 was isolated in cell culture and typed by molecular methods. Complete VP1 gene sequences were determined and analyzed. Specific E33 antibody was measured by virus neutralization testing. From June 3-20, 108 suspected cases were reported, and 19 were confirmed to be associated with E33 by laboratory testing, with seven virologically confirmed and 12 serologically confirmed cases. The suspected cases were in children aged 3-16 years (mean, 11 years), most of whom (94%, 102/108) were ≥6 years old. The majority of cases (98%, 106/108) presented as influenza-like illness (ILI), and two were clinically diagnosed as viral meningitis. Older children aged ≥12 years had a higher hospitalization rate (21%) than younger children (4%). A BLAST query of GenBank with the Hunan E33 strain VP1 gene sequence gave a close match to an E33 isolate from Pakistan, based on a partial VP1 gene sequence. Phylogenetic analyses of the complete E33 VP1 gene sequences from our study revealed an independent cluster with nucleotide sequences that diverge from E33 from other countries by >12%. Due to limited E33 VP1 gene sequence data in GenBank and passive EV surveillance in China and most other parts of the world (excepting hand, foot, and mouth disease surveillance in Asia), the approximate origin of Hunan E33 could not be determined.