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While final numbers won’t be available until the spring, 2012 looks like it will go down as one of the most active West Nile Fever seasons since the virus arrived in North America in 1999.
The CDC’s DVBID has released their final tally of cases for 2012 on their West Nile Update Page. They summarize the season thusly:
2012 West Nile virus update: December 11
This will be the last update for 2012 until final data are available in the spring of 2013.
As of December 11, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 5,387 cases of West Nile virus disease in people, including 243 deaths, have been reported to CDC. Of these, 2,734 (51%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 2,653 (49%) were classified as non-neuroinvasive disease.
The 5,387 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the second week in December since 2003. Eighty percent of the cases have been reported from 13 states (Texas, California, Louisiana, Illinois, Mississippi, South Dakota, Michigan, Oklahoma, Nebraska, Colorado, Arizona, Ohio, and New York) and a third of all cases have been reported from Texas.
Neuroinvasive cases (which present with meningitis, encephalitis, or flaccid Paralysis) are severe enough that they result in hospitalization and diagnosis, and so they are considered the best indicator of the scope of each year’s epidemic.
Mild cases – called West Nile Fever – often go undiagnosed, with probably only 2%-3% being identified.
Meaning that with more than 2,600 mild cases reported, the true incidence was probably in excess of 100,000 infections.
Hardest hit this year was Texas, with more than 1,700 cases and 76 deaths. Far behind, but in second place, was California with 461 cases and 16 deaths.
Nevertheless, the highest incidence of neuroinvasive disease occurred along the Gulf Coast and into the upper Mid West.
Earlier this year the CDC indicated they would be taking a look at this year’s WNV season to see if any changes have occurred in the virus to account for this sudden spike in activity.
While West Nile season has passed for most of the country, there are still a few areas where mosquitoes are still active. So, if you live in, or are visiting one of these areas, the advice by many health departments to follow the `5 D’s’ remains intact.
