Neuroinvasive disease cases, refers to severe cases of disease that affect a person’s nervous system. These include encephalitis which is an inflammation of the brain, meningitis which is an inflammation of the membrane around the brain and the spinal cord and acute flaccid paralysis which is an inflammation of the spinal cord that can cause a sudden onset of weakness in the limbs and/or breathing muscles.
Click here for further explanation of WN meningitis and/or encephalitis.
Click here for further explanation of acute flaccid paralysis

Nonneuroinvasive disease cases refers to typically less severe cases that show no evidence of neuroinvasion—primarily West Nile fever. 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.

See the case definition (2004) for Neuroinvasive and NonNeuroinvasive Domestic Arboviral Diseases.

Presumptive viremic donors (PVDs) are people who had no symptoms at the time of donating blood (people with symptoms are deferred from donating) through a blood collection agency, but whose blood tested positive in preliminary tests when screened for the presence of West Nile virus. Some PVDs do go on to develop symptoms after donation, at which point they would be included in the count of human disease cases by their state.

Total Human Cases Reported to CDC: These numbers reflect both mild and severe confirmed and probable human disease cases occurring between January 1, 2010 to December 31, 2010 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 2010 virus/disease activity is posted when such cases are reported to CDC.
Of the 1,021 WNV cases, 629 (62%) were reported as a neuroinvasive disease cases, and 392 (38%) as nonneuroinvasive disease cases. One hundred and forty four presumptive viremic donors have been reported at this time.
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 seroseroepidemiological survey. Lancet 2001;358:261-264.