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Neuroinvasive disease and West Nile virus infection, North Dakota, USA, 1999-2008.
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PMID:  22469465     Owner:  NLM     Status:  MEDLINE    
To determine risk for West Nile virus (WNV) neuroinvasive disease in North Dakota, we tested plasma samples from blood donors for WNV IgG and compared infection rates with reported WNV neuroinvasive disease incidence. We estimate that 1 in 244 WNV infections leads to neuroinvasive disease; risk is substantially increased among men and older persons.
Paul J Carson; Stephanie M Borchardt; Brian Custer; Harry E Prince; Joan Dunn-Williams; Valerie Winkelman; Leslie Tobler; Brad J Biggerstaff; Robert Lanciotti; Lyle R Petersen; Michael P Busch
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural    
Journal Detail:
Title:  Emerging infectious diseases     Volume:  18     ISSN:  1080-6059     ISO Abbreviation:  Emerging Infect. Dis.     Publication Date:  2012 Apr 
Date Detail:
Created Date:  2012-04-03     Completed Date:  2012-07-25     Revised Date:  2013-06-26    
Medline Journal Info:
Nlm Unique ID:  9508155     Medline TA:  Emerg Infect Dis     Country:  United States    
Other Details:
Languages:  eng     Pagination:  684-6     Citation Subset:  IM    
University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota, USA.
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MeSH Terms
Antibodies, Viral / blood
Meningitis, Viral / epidemiology*,  immunology,  virology
Middle Aged
North Dakota / epidemiology
Risk Factors
Seroepidemiologic Studies
West Nile Fever / epidemiology*,  immunology,  virology
West Nile virus / immunology*
Young Adult
Grant Support
Reg. No./Substance:
0/Antibodies, Viral

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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Journal Information
Journal ID (nlm-ta): Emerg Infect Dis
Journal ID (iso-abbrev): Emerging Infect. Dis
Journal ID (publisher-id): EID
ISSN: 1080-6040
ISSN: 1080-6059
Publisher: Centers for Disease Control and Prevention
Article Information

Print publication date: Month: 4 Year: 2012
Volume: 18 Issue: 4
First Page: 684 Last Page: 686
ID: 3309699
PubMed Id: 22469465
Publisher Id: 11-1313
DOI: 10.3201/eid1804.111313

Neuroinvasive Disease and West Nile Virus Infection, North Dakota, USA, 1999–2008 Alternate Title:Neuroinvasive Disease and West Nile Virus
Paul J. Carson
Stephanie M. Borchardt
Brian Custer
Harry E. Prince
Joan Dunn-Williams
Valerie Winkelman
Leslie Tobler
Brad J. Biggerstaff
Robert Lanciotti
Lyle R. Petersen
Michael P. Busch
University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota, USA (P.J. Carson, S.M. Borchardt);
Sanford Health, Fargo, North Dakota, USA (P.J. Carson);
Fargo Veterans Affairs Medical Center, Fargo (S.M. Borchardt);
Wisconsin Department of Health, Madison, Wisconsin, USA (S.M. Borchardt);
Blood Systems Research Institute, San Francisco, California, USA (B. Custer, L. Tobler, M.P. Busch);
Focus Diagnostics, Cypress, California, USA (H.E. Prince);
Creative Testing Solutions, Tempe, Arizona, USA (J. Dunn-Williams, V. Winkelman);
Centers for Disease Control and Prevention, Fort Collins, Colorado, USA (B.J. Biggerstaff, R. Lanciotti, L.R. Petersen);
University of California San Francisco, San Francisco (M.P. Busch)
Correspondence: Address for correspondence: Michael P. Busch, Blood Systems Research Institute, University of California San Francisco, 270 Masonic Ave, San Francisco, CA 94118, USA; email:

Human infection with West Nile virus (WNV) was first identified in North America in 1999 during an outbreak in New York City (NYC), New York, USA (1). Since that time, the ArboNET surveillance system housed in the Centers for Disease Control and Prevention (Atlanta, GA, USA) has documented the virus’ spread across the United States (2); incidence of disease was highest in the central plains (3). Because most persons with WNV infection remain asymptomatic or have West Nile fever, for which routine diagnostic testing is not recommended, the number of infections vastly exceeds the number of cases reported (4).

On the basis of an initial study of the 1999 outbreak in NYC, it was estimated that 1 case of neuroinvasive disease (meningitis, encephalitis, or acute flaccid paralysis) occurred for 140 WNV infections (5). This ratio is frequently quoted in the literature and has been used to develop national estimates for incidence of WNV infection (6). More recent data derived from blood donor screening suggested that WNV neuroinvasive disease (WNND) might occur as frequently as 1 case for 256–353 infections (7). Furthermore, surveillance data suggest that the proportion of infected persons in whom WNND develops varies markedly by age and sex (3). Previous studies have not clearly identified these differences or used age- and sex-adjusted proportions to estimate the cumulative incidence.

Understanding the full incidence of disease, including asymptomatic infections, is essential for preventing transfusion- and transplantation-associated infections. The purposes of this study were to define the cumulative WNV infection incidence spanning a decade in a highly disease-endemic area and to correlate this with the reported incidence of WNND.

The Study

Plasma from 6,999 sequential volunteer blood donations collected from November through December 2008 at North Dakota donation centers was archived at Creative Testing Solution’s donor screening laboratory in Tempe, Arizona, USA. Samples were selected to include only those from donors with a North Dakota residence as determined on the basis of postal codes. The resulting 4,514 samples were tested for WNV-specific IgG, and IgM if IgG test results were reactive, by using commercially available ELISAs (8) at Focus Laboratories (Cypress, CA, USA).

The cumulative number of infections by age and sex strata in the North Dakota population was estimated by multiplying the corresponding stratum-specific WNV-specific IgG seroprevalence of blood donors by the North Dakota population (US Census Bureau data, 2010). Because blood donors include only persons >16 years of age, the seroprevalence among persons <16 years of age could not be accurately estimated. Therefore, estimates were only calculated for the adult population. For the purposes of this report, adolescents 16–17 years of age are considered adults. The corresponding ratio of WNND cases to infections for each age and sex stratum was determined by dividing the estimated number of infections by the number of WNND cases reported in North Dakota with onset from the first reported case during 2002–2008.

We assessed specificity of the IgG response by examining a subset of 54 samples across the range of IgG responses (every 6th sample) of antibody levels in seropositive donors. We used WNV 90% plaque-reduction neutralization tests and Vero cells as described (9).

We calculated relative risks (RRs) and 95% CIs by using standard, asymptotic methods. We performed statistical analyses by using SAS version 9.2 (SAS Institute, Cary, NC, USA), Epi Info (Centers for Disease Control and Prevention), and R version 2.11.1 (

Of the 4,514 North Dakota blood donors whose plasma samples were tested, 2,349 (52%) were male. Data on race were available for 4,166 (92%) donors: 98% were white/non-Hispanic, 1% (40) were American Indian, and 0.2% (10) were black/non-Hispanic. Among 370 (8.2%) donors who were positive for WNV-specific IgG, 28 (7.5%) were positive for WNV-specific IgM, suggesting recent infection. All 54 representative IgG-reactive samples tested by plaque-reduction neutralization tests had WNV-specific neutralizing antibodies, confirming the specificity of the IgG assay results.

We estimate a total of 44,511 WNV infections in North Dakota residents from its 1999 introduction to the United States through 2008. Seroprevalence was highest among persons 16–24 years of age compared with all other ages combined (RR 1.8, 95% CI 1.2–2.6) and men (9.2%) compared with women (7.2%; RR 1.3, 95% CI 1.1–1.6), possibly reflecting differences in mosquito exposure (Table). Comparison of seroprevalence data with reported numbers of WNND cases in North Dakota indicated that WNND was more likely to develop in infected men than women (RR 1.3, 95% CI 1.0–1.8) and that age was a strong predictor for development of WNND (Table). Among persons ≥65 years of age, the risk was 1 in 54 (95% CI 1:43–1:67), ≈16.0× (95% CI 9.1–28.2) as high as that for persons in the youngest age group. Overall, the risk of WNND development after WNV infection was 1 in 244 (95% CI 1:213–1:286).


We estimated that during 1999 through 2008, >40,000 North Dakota residents were infected with WNV. WNND was ≈30% more likely in WNV-infected male than in WNV-infected female donors, and the risk for WNND markedly increased with age. We estimated that the chance of WNND development in WNV-infected persons >65 years of age was ≈1 in 50.

The findings of this large study of WNV expand on findings from previous seroprevalence studies (5,1015) and suggest that the incidence of WNND cases related to WNV infection in North Dakota is nearly half that estimated during the 1999 NYC epidemic (5). These findings are more consistent with those of our previous study (7), which estimated 256 infections for every case of WNND nationwide. That study was based on projections of infection rates from the yield of WNV nucleic acid amplification screening in blood donors across the United States, and it correlated those rates with the number of WNND cases nationwide reported to ArboNET in 2003.

The NYC study (5) might have overestimated the proportion of infections that resulted in WNND because of a smaller sample size with wider CIs and selection bias resulting from symptomatic persons preferentially enrolling in the survey. Similar to our study, the NYC study indicated that WNND developed in 1 of every 50 infected persons ≥65 years of age (5). Published studies have not stratified the risk for WNND by age and sex, which our data indicate are major considerations in projecting overall incidence of WNV infection rates from the number of WNND case reports. The ratio of cases of WNND to cases of WNV infections ranged from 1 in 50 to 1 in 1,231 from the groups with the highest risk (men >65 years of age) to lowest risk (women 16–24 years of age).

Our study has potential limitations. Blood donors might not represent the general population with regard to mosquito exposure. Also, blood donation is limited to persons >16 years of age; therefore, our analysis is limited to the adult population. The completeness of reporting of WNND cases to ArboNET is also unknown and could vary over time. In addition, differences in WNND rates based on race or ethnicity have not been reported in previous studies, and we were unable to explore these differences because the North Dakota blood donor pool was predominantly white.

Results of our study indicate that ≈1 in 12 North Dakota residents has been infected with WNV. The rate of WNV infection was greatest for younger persons and men. Among those infected with WNV, male sex and older age markedly increased the risk for development of WNND; WNND developed in ≈1 of 50 of the infected men >65 years of age. Prevention measures should be particularly targeted to this group during the summer WNV transmission season.


Suggested citation for this article: Carson PJ, Borchardt SM, Custer B, Prince HE, Dunn-Williams J, Winkelman V, et al. Neuroinvasive disease and West Nile virus infection, North Dakota, USA, 1999–2008. Emerg Infect Dis [serial on the Internet]. 2012 April [date cited].


We thank Abigail Schrock for assistance with composing the table and formatting the paper.

This work was funded in part by grants from the Centers for Disease Control and Prevention (R01-CI-000214) and the National Heart, Lung, and Blood Institute (RC2-HL-101632).

Dr Carson is chairman of the Department of Infectious Disease and director of Clinical Research at Sanford Health, Fargo, ND. His research interests include West Nile virus infection, antimicrobial drug stewardship, and nosocomial infections.

1. . NashD, MostashariF, FineA, MillerJ, O’LearyD, MurrayK, et al. The outbreak of West Nile virus infection in the New York City area in 1999.N Engl J Med. Year: 2001;344:1807–1410.1056/NEJM20010614344240111407341
2. . PetersenLR, HayesEBWestward ho?—The spread of West Nile virus.N Engl J Med. Year: 2004;351:2257–910.1056/NEJMp04826115564540
3. . LindseyNP, StaplesJE, LehmanJA, FischerMSurveillance for human West Nile virus disease—United States, 1999–2008.MMWR Surveill Summ. Year: 2010;59:1–1720360671
4. . ZouS, FosterGA, DoddRY, PetersenLR, StramerSLWest Nile fever characteristics among viremic persons identified through blood donor screening.J Infect Dis. Year: 2010;202:1354–6110.1086/65660220874087
5. . MostashariF, BunningML, KitsutaniPT, SingerDA, NashD, CooperMJ, et al. Epidemic West Nile encephalitis, New York, 1999: results of a household-based seroepidemiological survey.Lancet. Year: 2001;358:261–410.1016/S0140-6736(01)05480-011498211
6. . LindseyNP, KuhnS, CampbellGL, HayesEBWest Nile virus neuroinvasive disease incidence in the United States, 2002–2006.Vector Borne Zoonotic Dis. Year: 2008;8:35–4010.1089/vbz.2007.013718237264
7. . BuschMP, WrightDJ, CusterB, ToblerLH, StramerSL, KleinmanSH, et al. West Nile virus infections projected from blood donor screening data, United States, 2003.Emerg Infect Dis. Year: 2006;12:395–40210.3201/eid1203.05128716704775
8. . HogrefeWR, MooreR, Lape-NixonM, WagnerM, PrinceHEPerformance of immunoglobulin G (IgG) and IgM enzyme-linked immunosorbent assays using a West Nile virus recombinant antigen (preM/E) for detection of West Nile virus– and other flavivirus-specific antibodies.J Clin Microbiol. Year: 2004;42:4641–810.1128/JCM.42.10.4641-4648.200415472323
9. . OcegueraLFIII, PatirisPJ, ChilesRE, BuschMP, ToblerLH, HansonCVFlavivirus serology by Western blot analysis.Am J Trop Med Hyg. Year: 2007;77:159–6317620648
10. . MandalakasAM, KippesC, SedranskJ, KileJR, GargA, McLeodJ, et al. West Nile virus epidemic, northeast Ohio, 2002.Emerg Infect Dis. Year: 2005;11:1774–710.3201/eid1111.04093316318737
11. . MeyerTE, BullLM, Cain HolmesK, PascuaRF, Travassos da RosaA, GutierrezCR, et al. West Nile virus infection among the homeless, Houston, Texas.Emerg Infect Dis. Year: 2007;13:1500–318257995
12. . SchweitzerBK, KramerWL, SambolAR, MezaJL, HinrichsSH, IwenPCGeographic factors contributing to a high seroprevalence of West Nile virus–specific antibodies in humans following an epidemic.Clin Vaccine Immunol. Year: 2006;13:314–810.1128/CVI.13.3.314-318.200616522771
13. . SchellenbergTL, AndersonME, DrebotMA, VooghtMT, FindlaterAR, CurryPS, et al. Seroprevalence of West Nile virus in Saskatchewan’s Five Hills Health Region, 2003.Can J Public Health. Year: 2006;97:369–7317120874
14. . MurphyTD, GrandpreJ, NovickSL, SeysSA, HarrisRW, MusgraveKWest Nile virus infection among health-fair participants, Wyoming 2003: assessment of symptoms and risk factors.Vector Borne Zoonotic Dis. Year: 2005;5:246–5110.1089/vbz.2005.5.24616187893
15. . MichaelsSR, BalsamoGA, KukrejaM, AndersonC, Straif-BourgeoisS, TalatiG, et al. Surveillance for West Nile virus cases in Louisiana 2001–2004.J La State Med Soc. Year: 2005;157:269–7216374972

[TableWrap ID: T1] Table  Correlation of WNV IgG seroprevalence among blood donors with WNND, by sex and age group, North Dakota, USA, 2002–2008*
Sex and age group, y No. donors Seroprevalence, % (95% CI) Seropositivity, RR (95% CI) Total population† WNV-infected population‡ No. WNND cases§ Ratio of WNND cases to WNV infections (95% CI) WNND, RR (95% CI) Inverse of ratio¶
Male 2,349 9.2 (6.1–8.3) 279,252 26,122 119 0.0045 
(0.0038–0.0054) 220
16–24 321 12.8 (9.1–16.4) Referent 56,156 7,188 10 0.0014 (0.0008–0.0026) Referent 719
25–44 562 8.7 (6.4–11.1) 0.7 (0.5–1.0) 89,968 7,827 22 0.0028 (0.0018–0.0042) 2.0 
(1.0–4.2) 356
45–64 1,132 9.3 (7.6–11.0) 0.7 (0.5–1.0) 90,701 8,435 34 0.0040 (0.0029–0.0056) 2.9 (1.4–5.9) 248
≥65 334 6.3 (3.7–8.9) 0.5 (0.3–0.8) 42.427 2,672 53 0.0198 (0.0152–0.0258) 14.3 (7.3–28.0) 50
Female 2,165 7.2 (6.2–8.3) 271,968 18,353 63 0.0034
(0.0027–0.0044) 291
16–24 316 9.8 (6.5–13.1) Referent 50,274 4,926 4 0.0008 (0.0003–0.09) Referent 1,231
25–44 600 6.7 (4.7–8.7) 0.7 (0.4–1.1) 78,869 5,284 16 0.0030 (0.0018–0.0049) 3.7 (1.2–11.1) 330
45–64 1,010 7.5 (5.9–9.2) 0.8 (0.5–1.1) 87,775 6,583 17 0.0026 (0.0016–0.0042) 3.2 (1.1–9.4) 387
≥65 239 2.9 (0.8–5.1) 0.3 (0.1–0.7) 55,050 1,596 26 0.0163
(0.0111–0.0241) 20.1
(7.0–57.4) 61
Total 4,514 8.2 (7.4–9.0) 551,220 44,511 182 0.0041
(0.0035–0.0047) 244

*WNV, West Nile virus; WNND, WNV neuroinvasive disease; RR, relative risk.
†Source: US Census Bureau, 2010.
‡Seroprevalence × population.
§Data from Centers for Disease Control and Prevention; ArboNET.
¶No. WNV infections/no. WNND cases.

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Keywords: Keywords: West Nile virus, viruses, epidemiology, serology, incidence, blood donors, neuroinvasive disease, meningitis, encephalitis, flaccid paralysis, arbovirus, flavivirus, North Dakota, United States, vector-borne infections.

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