since 2004, the disease must be reported to cdc (passive surveillance, arbonet). jcv has been mostly reported in adults rather than in children (median age 48 years versus 8 years), and is more likely to cause meningitis than encephalitis compared to illness caused by la crosse virus. it also occurs throughout the summer (may until september), or even throughout the year rather than mostly in august, which may be due to the diversity of mosquitoes it can infect.