A new variant of echovirus 4 associated with a large outbreak of aseptic meningitis

Background: A large outbreak of aseptic meningitis which began in April 199 7 involved hundreds of cases in all geographical regions of Israel and the Palestinian Authority, peaked between June and September, and lasted until December. Objectives: We have investigated the virus associated with the outbreak to determine its serotype and molecular type and to establish epidemiological links. Design: Virus strains isolated from 210 clinical samples were serotyped by neutralization using LBM and WHO antiserum pools and two echovirus 4 (EV4)- specific antisera, and by immunofluorescence using a monoclonal antibody. R NA was extracted and a 435 base long fragment derived from the 5'UTR of the genome was amplified by RT-PCR using common primers, and sequenced. Sequen ces were compared to echoviruses 4, 6 and 7 prototypes from ATCC,and to oth er echoviruses sequences from the EMBL/Genbank data base. Results: The outbreak isolates were identified by the EV4 type-specific ant isera and the monoclonal antibody but not with the WHO pools. Very few isol ates could be typed by the LBM pools. The EV4 isolates accounted for 68% of all enterovirus isolates in our laboratory in 1997. The age distribution o f the patients was: 0-11 month, 11.2%; 1-4 years, 16.1%; 5-9 years, 31.8%; 10-14 years, 9.9%; 15-20 years, 9.5%; 21-44 years, 21.5%; and >45 years, 0% . Males between I and 14 years of age were affected more frequently than fe males of the same age. The sequences of 25 of 28 EV4 isolates analyzed were closely related to each other (> 95% homology) and the remaining three iso lates had < 95% homology to the others and to each other. Interestingly, th e outbreak strains were less closely related to the EV4 prototype, than to several other echoviruses. Three closely related subgroups were identified which correlated with geographical distribution but the temporal distributi on did not reveal links leading to the source of the outbreak. Conclusion: The outbreak was caused by a variant of EV4 which apparently di d not circulate in the area before and thus was capable of causing a widesp read infection. (C) 1999 Elsevier Science B.V. All rights reserved.