West Nile encephalitis and West Nile meningitis are forms of severe disease that affect a person’s nervous system. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord.
Click here for further explanation of WN meningitis and/or encephalitis.
West
Nile fever refers to typically less severe cases
that show no evidence of neuroinvasion.
WN fever is considered a notifiable disease, however the number of cases reported
(as with all diseases) may be limited by whether persons affected seek care, whether
laboratory diagnosis is ordered and the extent to which cases are reported to health
authorities by the diagnosing physician.
Other
Clinical includes persons with clinical manifestations
other than WN fever, WN encephalitis or WN meningitis,
such as acute flaccid paralysis. Clinical/Unspecified cases
are those for which sufficient clinical information was
not provided.
Total
Human Cases Reported to CDC for 2003- These
numbers reflect both mild and severe human disease cases
occurring
between Jan.1 -Dec. 31, 2003 that have been reported
to ArboNET by state and local health departments. ArboNET
is the national, electronic surveillance system established
by CDC to assist states in tracking West Nile virus and
other mosquito-borne viruses. Information regarding 2004
virus/disease activity will be posted when such cases
are
reported to CDC.
Of 9862 cases,
6830 (69%) were reported as West Nile fever (milder
disease),
2866 (29%) were reported as West Nile meningitis or encephalitis
(neuroinvasive disease) and 166 (2%) were clinically
Clinical/Unspecified. Please
refer to state health department
web sites for further details regarding state case totals.
Note: The
high proportion of neuroinvasive disease cases among
reported cases of West Nile virus disease reflects
surveillance reporting bias. Serious cases are more
likely to be reported than mild cases. Also, the surveillance
system is not designed to detect asymptomatic infections. Data
from population-based surveys indicate that among all
people who become infected with West Nile virus (including
people with asymptomatic infections) less than 1% will
develop severe neuroinvasive disease. See: Mostashari
F, Bunning ML, Kitsutani PT, et al. Epidemic West Nile
Encephalitis, New York, 1999: Results of a household-based
seroepidemiological survey. Lancet 2001;358:261-264.
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