West Nile Virus Incidence Rate and Case Numbers as of December 2012

CDC continues to report cases of West Nile Virus, even this late in the season.  Forty-eight states have reported infection in birds, people and/or mosquitoes.  As of December 11, 2012, a  total of 5,387 cases of West Nile virus disease in people, including 243 deaths, have been reported to CDC.  About half the cases were classified as neuroinvasive disease (such as meningitis or encephalitis) and half 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.

In addition to case numbers it is also important to look at Incidence Rate or cases per 100,000 people.  Note a number of the states listed above which contributed to 80% of the cases had a low incidence rate such as New York and Ohio and other states such as South and North Dakota, Texas, Louisiana, Arizona, and Illinois have high case numbers and high incidence rates.

WNV Neuroinvasive Disease as of 11 Dec 2012
2012 Population NID cases Incidence (cases per 100,000 population)
South Dakota 824,082 62 7.5
North Dakota 683,932 39 5.7
Mississippi 2,978,512 103 3.5
Louisiana 4,574,836 155 3.4
Texas 25,674,681 785 3.1
Oklahoma 3,791,508 101 2.7
Nebraska 1,842,641 40 2.2
Arkansas 2,937,979 44 1.5
Illinois 12,869,257 184 1.4
Michigan 9,876,187 138 1.4
Arizona 6,482,505 82 1.3
Colorado 5,116,796 62 1.2
New Mexico 2,082,224 24 1.2
District of Columbia 617,996 6 1.0
United States 311,591,917 2734 0.9
California 37,691,912 278 0.7
Indiana 6,516,922 45 0.7
Alabama 4,802,740 33 0.7
Wisconsin 5,711,767 39 0.7
Kansas 2,871,238 19 0.7
Ohio 11,544,951 76 0.7
Minnesota 5,344,861 34 0.6
Wyoming 568,158 3 0.5
Georgia 9,815,210 42 0.4
South Carolina 4,679,230 20 0.4
Maryland 5,828,289 24 0.4
Iowa 3,062,309 11 0.4
Massachusetts 6,587,536 23 0.3
Connecticut 3,580,709 12 0.3
Idaho 1,584,985 5 0.3
New York 19,465,197 60 0.3
Tennessee 6,403,353 18 0.3
West Virginia 1,855,364 5 0.3
Missouri 6,010,688 16 0.3
New Jersey 8,821,155 22 0.2
Virginia 8,096,604 20 0.2
Florida 19,057,542 46 0.2
Delaware 907,135 2 0.2
Pennsylvania 12,742,886 28 0.2
Rhode Island 1,051,302 2 0.2
Nevada 2,723,322 5 0.2
Vermont 626,431 1 0.2
Utah 2,817,222 3 0.1
Montana 998,199 1 0.1
Kentucky 4,369,356 4 0.1
New Hampshire 1,318,194 1 0.1
Maine 1,328,188 1 0.1
North Carolina 9,656,401 6 0.1
Washington 6,830,038 4 0.1
Alaska 722,718 0 0.0
Hawaii 1,374,810 0 0.0
Oregon 3,871,859 0 0.0

Table provided by SD DOH, Dr. Lon Kightlinger, State Epidemiologist

Kim Cassel


CDC: Hurricane Isaac and West Nile Virus

CDC Telebriefing on West Nile Virus Update

Wednesday, August 29 at Noon ET

I have taken the following excerpts from the press briefing transcript as they speak to Isaac and potential for increasing cases of West Nile Virus –  the bottom line is no dramatic increase is anticipated and  Lyle Petersen explains why they do not expect Isaac to contribute to the number of cases of WNV.

LYLE PETERSEN: And now I’d like to say a few words about Hurricane Isaac and the question of how it might affect the spread of West Nile virus. Previous experience has shown that floods and hurricanes do not typically result in increased transmission of West Nile virus. Thus, we expect Hurricane Isaac will likely have no noticeable effect on the current West Nile epidemic. Nevertheless, small increases in the numbers of West Nile cases were noted in some areas of Louisiana after Hurricane Katrina. These were thought to be due to increased outdoor exposure that occurred when houses were severely damaged and during recovery efforts. CDC has reached out to health departments in Louisiana, Mississippi, Alabama, and Tennessee to alert them of the situation and offer assistance. In light of the ongoing risk for West Nile virus infection, it’s important for people to protect themselves from mosquito bites.

We encourage everyone to use insect repellent when you go outdoors, wear long sleeves and pants. Use air conditioning if possible. Empty stands water from items outside your home, such as gutters, kiddie pools and birdbaths. In response to this year’s outbreak, CDC works closely with state and local health departments particularly in areas hardest hit by the epidemic. As I noted earlier, nearly half of this year’s West Nile virus cases have occurred in Texas. A majority of the cases there have been in the Dallas area. CDC has had the privilege of working with the Texas department of state health services in Dallas County and other county departments to help protect people from the West Nile virus. They’ve done a great job. Dr. Lakey is going to give an update about the situation in Texas. Dr. Lakey?

ELIZABETH WEISS: Thank you so much for taking my call. I had a question about the point that was made earlier, looking at the hurricane, you said that there had historically been an uptick, is that right after? You assume because there was so much standing water, the services that might have gone to mosquito abatement may have been used elsewhere, an uptick later do you mean never or later?

LYLE PETERSEN: What has been observed in the past, we have had a lot of experience with vector-borne diseases and hurricanes and floods? What has been observed in the past that these don’t really have a big impact on overall incident of disease. The reason is, because, it’s because, these hurricanes and flood events tend to disrupt the entire ecology of the area and interrupt this natural transmission cycle between birds and mosquitoes. The virus normally exists in. And so, the end result is, really hurricanes and floods don’t have a major impact on our virus transmission. But, naturally, before the hurricane happened, there were plenty of West Nile virus infected mosquitoes out there in the environment. And so, what happens — what was observed in Louisiana, was, after Katrina, was that, people who were out, houses were destroyed. They were living out in the elements; there were a lot of workers out there and homeowners taking care of downed trees and the like. Outdoors and exposed to the West Nile virus-infected mosquitos already there. In some areas, where it was looked at, there was a small transient increase in West Nile virus transmission following hurricane Katrina, but if you look at the overall picture the hurricane really is not expected to have a major impact at all on what’s happening across the country.




E. Kim Cassel, Ph.D.