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Home News CDC West Nile Virus Update — September 2012

CDC West Nile Virus Update — September 2012

Public Health

As of September 4, 2012, a total of 1,993 cases of West Nile virus disease in people, including 87 deaths, have been reported to CDC.

| September 7, 2012

Editor’s note: The Centers for Disease Control and Prevention provided the following West Nile virus update on Sept. 4th

As of September 4, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes.  The only states not reporting West Nile activity are Alaska and Hawaii.  Forty-four states have reported at least one human case.  A total of 1,993 cases of West Nile virus disease in people, including 87 deaths, have been reported to CDC.  Of these, 1,069 (54 percent) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 924 (46 percent) were classified as non-neuroinvasive disease.  For comparison, the numbers reported last week were 1,590 total cases, 889 neuroinvasive disease cases, and 66 deaths. So, this week numbers represent about a 25 percent increase over last week. The 1,993 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the first week in September since West Nile virus was first detected in the United States in 1999.  As was true last week, over 70 percent of the cases have been reported from the following six states: Texas, South Dakota, Mississippi, Oklahoma, Michigan, and Louisiana.  And nearly 45 percent of all cases have been reported from Texas.

Based on past epidemics of West Nile disease, we expect the numbers will eventually show that this year’s epidemic peaked in mid- to late-August.  Although we may be past the historical peak, we expect that a great many cases of West Nile virus disease have not yet been reported, largely because of the lag between when a person gets sick and when the illness is reported.  Even if West Nile virus transmission were to stop today, we would continue to see reports of cases for several weeks.  

With regard to Hurricane Isaac, we have been consulting with officials in Louisiana, Mississippi, and other states since the storm made landfall.  Both our CDC program and the public health departments of southern and eastern coastal states have considerable experience in assessing the public health impact of hurricanes and floods. In general, experiences shown that such disasters do not increase the transmission of West Nile virus and other arboviruses.  However, small increases in the numbers of West Nile virus cases can occur, as was reported in several areas of Louisiana after Hurricane Katrina in 2005.  These cases were thought to be due to the unavoidable increased outdoor exposure people experienced when their houses were damaged and during recovery efforts.  Rain and flooding events can produce conditions that lead to explosive increases in mosquito populations, which in turn can pose a terrible nuisance to residents and those helping with recovery.  Aerial spraying of insecticide is sometimes used after hurricanes to control nuisance mosquitos.  CDC will continue to offer technical assistance to Louisiana, Mississippi, and other states affected by Hurricane Isaac. 

In Texas, we are working with public health officials to contain the outbreak in various communities, including Dallas County.  One way that we’ve done this is through CDC’s “Epi-aid” process.  Here’s how it works.  CDC’s Epi-aid teams, which include investigators from our Epidemic Intelligence Service, are deployed at the request of states to help tackle urgent public health problems.  CDC does this in collaboration with state and local health departments – so it’s not a matter of CDC coming in and taking over the response.  This interaction among federal, state, and local authorities has been crucial to the rapid response in Texas.

Two CDC Epi-aid teams have recently returned from deployments to Texas.  One team, which was based in Austin from August 20 to 31, helped review and describe West Nile cases in Texas, evaluated electronic laboratory reports to estimate the numbers and trends in human cases, and assessed differences in West Nile virus seasons during the past decade.  The second team, which was based in Arlington from August 20 to September 4, worked closely with Texas officials to collect data for human and mosquito surveillance, and for evaluating the impact of insecticide spraying.  In just a moment, Dr. Lakey will share some of the preliminary results from the Arlington team’s work. 

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