Protective behavior and West Nile virus risk.We conducted a cross-sectional, household survey in Oakville, Ontario Oakville (2006 population 165,613[2]) is a town on Lake Ontario in southern Ontario, Canada, midway between Toronto (about 31 km or 19 mi away) on its eastern border and Hamilton (about 20 km or 12 mi away) from its western border. , where an outbreak of West Nile virus West Nile virus, microorganism and the infection resulting from it, which typically produces no symptoms or a flulike condition. The virus is a flavivirus and is related to a number of viruses that cause encephalitis. (WNV WNV West Nile Virus WNV World Net Visions ) in 2002 led to an unprecedented number of cases of meningitis and encephalitis encephalitis (ĕnsĕf'əlī`təs), general term used to describe a diffuse inflammation of the brain and spinal cord, usually of viral origin, often transmitted by mosquitoes, in contrast to a bacterial infection of the meninges . Practicing [greater than or equal to] 2 personal protective behavior traits reduced the risk for WNV infection by half. ********** Little is known about risk factors for infection with West Nile virus (WNV). Data about the effect of personal protective behavior traits recommended by public health agencies, such as wearing long sleeves and long pants, using mosquito repellent, and avoidance of mosquito areas, are sparse (1). A household-based seroprevalence seroprevalence Immunology The proportion of a population that is seropositive–ie, has been exposed to a particular pathogen or immunogen; the seropositivity of a population is calculated as the number of individuals who produce a particular antibody divided survey in Oakville, Ontario, where a large outbreak of WNV occurred in the summer of 2002, allowed us to assess modifiable risk factors for WNV infection. Oakville is located in Halton, a region that had the highest reported incidence of clinical WNV infection in Ontario in the 2002 season. Sixty cases (58 confirmed and 2 probable) occurred in a population of almost 400,000, with onset during the months of August and September 2002 (Figure 1). Apeak a·peak adv. & adj. Nautical In a vertical or almost vertical position or direction: rowers holding their oars apeak. in dead crow sightings in Halton (600 per week) occurred 5 weeks before the peak in human cases. Within this region, most cases occurred in south Oakville, in the L6L and L6K forward sortation Identifying objects that are stamped with a bar code and routing them to the appropriate destination. Sortation is typically a high-speed process used in the transportation industry by companies such as Federal Express, UPS and others. See sort and bar code. areas (FSAs, i.e., the first 3 digits of the postal code Noun 1. postal code - a code of letters and digits added to a postal address to aid in the sorting of mail postcode, ZIP code, ZIP code - a coding system used for transmitting messages requiring brevity or secrecy ) (Figure 2). We hypothesized that personal protective and source-reduction behavior would be associated with reduced risk for WNV infection. [FIGURES 1-2 OMITTED] The Study The survey was conducted from March to April 2003. Households in the L6L and L6K FSAs of south Oakville were selected with random digit dialing Random digit dialing (RDD) is a method for selecting people for involvement in telephone statistical surveys by generating telephone numbers at random. Random digit dialing has the advantage that it includes unlisted numbers that would be missed if the numbers were selected from a . Within households, a randomly selected household member [greater than or equal to] 18 years of age was invited to participate. Given that pediatric pediatric /pe·di·at·ric/ (pe?de-at´rik) pertaining to the health of children. pe·di·at·ric adj. Of or relating to pediatrics. neuroinvasive disease is rare, children were excluded (2). The 2001 census population of these areas that was [greater than or equal to] 18 years of age was 30,467. After verbal consent was obtained, respondents were administered a standardized telephone survey. Survey data were collected for respondents who resided in the study area from July 1 to September 30, 2002. Single serum samples were collected from March 23 to June 5, 2003 (specimen collection was interrupted from March 29 to April 16 because of severe acute respiratory syndrome Severe Acute Respiratory Syndrome (SARS) Definition Severe acute respiratory syndrome (SARS) is the first emergent and highly transmissible viral disease to appear during the twenty-first century. ), from persons who had completed the survey. Respondents were unaware of their serologic se·rol·o·gy n. pl. se·rol·o·gies 1. The science that deals with the properties and reactions of serums, especially blood serum. 2. status at the time of the telephone interview, which reduced the possibility for recall bias. Samples were collected and stored at -70[degrees]C until they were tested. Each sample was tested with Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. WNV enzyme immunoassay Immunoassay An assay that quantifies antigen or antibody by immunochemical means. The antigen can be a relatively simple substance such as a drug, or a complex one such as a protein or a virus. immunoglobulin (Ig) G. Reactive samples were forwarded to Health Canada's National Viral Zoonotic Zoonotic A disease which can be spread from animals to humans. Mentioned in: Zoonosis Laboratory in Winnipeg for plaque reduction neutralization tests (PRNT) against West Nile West Nile may refer to:
or breakbone fever or dandy fever Infectious, disabling mosquito-borne fever. Other symptoms include extreme joint pain and stiffness, intense pain behind the eyes, a return of fever after brief pause, and a characteristic rash. , and St. Louis encephalitis St. Louis encephalitis see St. Louis encephalitis. viruses (3). Since our case definition relied on IgG, a positive result may have been caused by infection before the outbreak. However, the prevalence would have been low and would not likely affect our results; surveillance for WNV in Ontario began in 2000, and no positive clinical specimen was seen until the 2002 outbreak (4). The ethics review board at McMaster University approved the study. Based on an assumed population of 30,500, for a prevalence as low as 1%, a sample of 1,500 allows for 95% confidence interval confidence interval, n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%. (CI) from 0.5% to 1.5%, and for a prevalence as high as 4% the sample allows 95% CI from 3% to 5%. Initially, 1,500 persons completed the survey, but not all consented to provide a blood sample. As a result, an additional 150 persons were surveyed in April of 2003 to achieve the required sample. Of the 1,650 persons surveyed, 1,505 (91%) consented to provide a blood sample. This fraction represented 25% of persons initially contacted about the study. No significant differences were found in demographic characteristics, so the 2 groups were pooled for subsequent analysis. Because our sample did not correspond in age to the 2001 population (Table 1), we standardized our sample by using age-specific WNV seroprevalences. To assess risk factors for WNV infection, we conducted a univariate analysis with chi-square test chi-square test: see statistics. to assess categorical variables and Student t test to assess differences between infected and uninfected persons. Multivariable analysis with logistic regression was performed by using a backwards, stepwise stepwise incremental; additional information is added at each step. stepwise multiple regression used when a large number of possible explanatory variables are available and there is difficulty interpreting the partial regression approach, selecting 1 variable from each category to include in the model (indoor exposures, outdoor exposures, personal behavior, source-reduction behavior) if the p value was <0.10. Forty-six (3.1% [95% CI 2.2%-4.0%]) of the 1,505 persons who provided a blood sample tested positive for WNV IgG, which was confirmed by PRNT. Two (6%) respondents 18-24 years of age, 7 (2%) respondents 25-44 years of age, 26 (4%) respondents 45-64 years of age, and 11 (2%) respondents >65 years of age were infected. In addition to the 46 participants, 14 persons were positive for WNV by IgG enzyme-linked immunosorbent assay enzyme-linked immunosorbent assay n. ELISA. Enzyme-linked immunosorbent assay (ELISA) A diagnostic blood test used to screen patients for AIDS or other viruses. but were negative by PRNT. Of these, 11 showed evidence of dengue IgG on PRNT confirmatory testing. No positive respondent had evidence of antibodies to St. Louis encephalitis virus on PRNT testing. The overall estimate of 3.1% did not change based on the 2001 census after adjusting for age. Within the 2 FSAs from which the sample was drawn were 6 patients with encephalitis (all hospitalized), 5 with meningitis (1 hospitalized), and 8 with WNV fever (1 hospitalized). The calculated rate of WNV illnesses was 47 per 100,000 population in the L6L area and 54 per 100,000 in the L6K area (Figure 2). Cases were defined by the attending physician's diagnosis. No cases of meningitis or encephalitis were seen in persons <50 years of age. Five cases of meningitis and 1 case of encephalitis were seen in persons 50-64 years of age; 2 cases of encephalitis were seen among those 65-74 years, and 3 cases of encephalitis were seen in persons [greater than or equal to] 75 years. Cases were ascertained by the Halton Region Health Department, which did epidemiologic follow-up on all patients with positive WNV serologic results. If we extrapolate extrapolate - extrapolation the 2.2%-4.0% range to the entire population of adults in the areas studied (30,467), an estimated 670-1,219 persons were infected with WNV in the L6L and L6K areas in the summer of 2002. The ratio of persons with severe illness (defined as meningitis or encephalitis) to asymptomatic or mild cases is, therefore, 1:85 (95% CI 1:60-1:110). Results of the univariate analysis to assess modifiable risk factors for infection are shown in Table 2. Having an open deck or unscreened porch, time spent outside at dusk or dawn on a work day, time spent outside at dusk or dawn on a nonwork day, and total time spent outside on a nonwork day were associated with WNV infection. Personal behavior associated with WNV infection included rarely or never avoiding areas where mosquitoes are likely to be a problem, rarely or never avoiding going outdoors, and rarely or never wearing long sleeves or long pants when outdoors. However, when [greater than or equal to] 2 personal risk reduction behavior traits were followed, the effect was protective. The following variables were entered in the multivariate model: open deck or unscreened porch, time spent outside at dusk or dawn on a nonwork day, and practicing [greater than or equal to] 2 personal protective behavior traits. Time spent outside at dusk or dawn on a nonwork day (adjusted odds ratio [OR] 1.47 per hour, 95% CI 1.22-1.8, p = 0.001) and practicing [greater than or equal to] 2 personal protective behavior traits (adjusted OR 0.46, 95% CI 0.25-0.84, p = 0.011) were kept in the final model. Conclusions We found in multivariable analysis that respondents who practiced [greater than or equal to] 2 personal protective behavior traits (avoidance of exposure to mosquitoes, wearing long sleeves and pants, using mosquito repellent) had [approximately equal to] 50% reduction in risk of infection. We also found that time spent outside at dusk or dawn on a nonwork day was a significant risk factor for WNV infection, which is consistent with findings from a previous report (1). Finding mosquitoes in the home was not associated with WNV infection, as it was in a previous report (5). The seroprevalence in Oakville in 2002 (3%) was within the range of previous reports (1,6,7). Given the emerging evidence on the long-term sequelae sequelae Clinical medicine The consequences of a particular condition or therapeutic intervention of WNV infection (8-13), preventing WNV infection is a public health priority. This study is the first to provide evidence to support the benefit of personal protective behavior in reducing risk for WNV infection. Financial support for this study was received from the Ontario Ministry of Health and Long-term Care long-term care (LTC), n the provision of medical, social, and personal care services on a recurring or continuing basis to persons with chronic physical or mental disorders. . Dr Loeb is supported by the Canadian Institutes for Health Research. Dr Loeb is an infectious diseases specialist and medical microbiologist. He holds a joint appointment as associate professor in the Departments of Pathology and Molecular Medicine and Clinical Epidemiology and Biostatistics, McMaster University. His research interests include emerging infectious diseases, infections in the elderly, and hospital infection control. References (1.) Mostashari F, Bunning ME, Kitsutani PT, Singer DA, Nash D, Cooper MJ, et al. Epidemic West Nile encephalitis. New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of , 1999: results of a house-hold based seroepidemiologic study. Lancet. 2001;358:261-4. (2.) Nash D, Mostashari F, Fine A, Miller J, O'Leary D, Murray K, et al. The outbreak of West Nile virus infection in the New York City New York City: see New York, city. New York City City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. area in 1999. N Engl J Med. 2001;344:1807-14. (3.) Beaty BJ, Calisher CH, Shope RS. Arboviruses arboviruses (ar´bōvī´r  sz),n. . In: Schmidt N J, Emmons RW, editors. Diagnostic procedures for viral, rickettsial rickettsial /rick·ett·si·al/ (ri-ket´se-al) pertaining to or caused by rickettsiae. rick·ett·si·al adj. Relating to, or caused by a member of the genus Rickettsia. and chlamydial chlamydial pertaining to members of the family Chlamydiaceae. chlamydial abortion abortion in cows, ewes, sows and goat does caused by Chlamydophila abortus and C. pecorum. See enzootic abortion of ewes. infections. 6th ed. Washington: American Public Health Association The American Public Health Association (APHA) is Washington, D.C.-based professional organization for public health professionals in the United States. Founded in 1872 by Dr. Stephen Smith, APHA has more than 30,000 members worldwide. ; 1989. p. 797-856. (4.) Ford-Jones EL, Fearon M, Leber C, Dwight P, Myszak M, Cole B, et al. Human surveillance for West Nile virus infection in Ontario in 2000. CMAJ CMAJ Canadian Medical Association Journal . 2002;166:29-35. (5.) Han LL, Popovici F, Alexander JP Jr, Laurentia V, Tengelsen LA, Cernescu C, et al. Risk factors for West Nile virus infection and meningoencephalitis meningoencephalitis /me·nin·go·en·ceph·a·li·tis/ (me-ning?go-en-sef?ah-li´tis) inflammation of the brain and meninges. toxoplasmic meningoencephalitis , Romania, 1996. J Infect Dis. 1999:179:230-3. (6.) Tsai TF, Popvici F, Cernescu C, Campbell GL, Nedelcu NI. West Nile encephalitis epidemic in southeastern Romania. Lancet. 1998;352:767-71. (7.) Centers for Disease Control and Prevention. Serosurveys for West Nile virus infection: New York and Connecticut counties, 2000. MMWR MMWR Morbidity & Mortality Weekly Report Epidemiology A news bulletin published by the CDC, which provides epidemiologic data–eg, statistics on the incidence of AIDS, rabies, rubella, STDs and other communicable diseases, causes of mortality–eg, Morb Mortal Wkly Rep. 2001;50:37-9. (8.) Sejvar JJ, Haddad MB, Tierney BC, Campbell GL, Martin AA, van Gerpen JA, et al. Neurological manifestations and outcome of West Nile virus infection. JAMA JAMA abbr. Journal of the American Medical Association . 2003;290:511-5. (9.) Pepperell C, Rau N, Krajden S, Kern R, Humar A, Mederski B, et al. West Nile virus infection in 2002: morbidity and mortality Morbidity and Mortality can refer to:
(10.) Weiss D, Carr D, Kellachan J, Tan C, Phillips M, Bresnitz E, et al. Clinical findings of West Nile virus infection in hospitalized patients, New York and New Jersey, 2000. Emerg Infect Dis. 2001;7:654-8. (11.) Emig M, Apple DJ. Severe West Nile virus disease in healthy adults. Clin Infect Dis. 2004;38:289-92. (12.) Watson JT, Pertel PE, Jones RC, Siston AM, Paul WS, Austin CC, et al. Clinical characteristics and functional outcomes of West Nile fever West Nile fever West Nile meningoencephalitis Infectious disease An acute, mosquito-borne flaviviral infection endemic–rarely, epidemic–in the Near East, Africa, former Soviet Union, India Clinical After a 3-6 day incubation, children present with a . Ann Intern Med. 2004; 141:360-5. (13.) Klee AL, Maidin B, Edwin B, Poshni I, Mostashari F, Fine A, et al. Long-term prognosis for clinical West Nile virus infection. Emerg Infect Dis. 2004;10:1405-11. Mark Loeb, * Susan J. Elliott, * Brian Gibson, ([dagger]) Margaret Fearon, ([dagger]) Robert Nosal, ([double dagger]) Michael Drebot, ([section]) Colin D'Cuhna, ([double dagger]) Daniel Harrington, * Stephanie Smith, * Pauline George, ([double dagger]) and John Eyles * * McMaster University, Hamilton, Ontario, Canada; ([dagger]) Ontario Ministry of Health and Long-term Care, Toronto, Ontario, Canada; ([double dagger]) Halton Region Health Department, Oakville, Ontario, Canada; and ([section]) Health Canada, Winnipeg, Manitoba, Canada Address for correspondence: Mark Loeb, McMaster University, 1200 Main St W, MDCL 3200 Hamilton, Ontario, LSN LSN Learning and Skills Network (UK) LSN Log Sequence Number LSN Large Scale Networking LSN Legal Services Network (American Association of Retired Persons) LSN Logical Sector Numbers LSN Leukosialin 3Z5, Canada; fax: 905-389-5822: email: loebm@mcmaster.ca
Table 1. Age and sex of south Oakville, Ontario, survey respondents
compared to 2001 census population
2001 population
age [greater
Respondents, than or equal to]18
n (%) years, n (%)
Characteristics (N = 1,650) (N = 30,467)
Sex
Female 827 (50) 16,015 (53)
Male 823 (50) 14,452 (47)
Age (y)
18-24 31 (2) 4,045 (13)
25-44 404 (24) 10,740 (34)
45-64 679 (41) 9,465 (30)
[greater than or equal to]65 531 (32) 7,510 (24)
Education
Completed high school 1519 (92) 27,040 (93)
Did not complete high school 116 (7) 2,085 (7)
No answer 15 (1)
Table 2. Risk factors for West Nile virus (WNV) infection among
household members in south Oakville, Ontario *
No. (%) respondents
or mean (SD)
Characteristic Seropositive Seronegative
(n = 46) (n = 1,459)
Indoor exposures
Open deck or unscreened
porch on home 40 (87) 1074 (74)
Tears in screens 12 (26) 343 (24)
Mosquitoes in home
[greater than or
equal to]1x/wk 10 (22) 314 (22)
Outdoor exposures
Time outside at dusk or
dawn on work day (h) 2.7 (1.5) 2.1 (1.4)
Total time outside on
a work day (h) 6.01 (3.9) 5.0 (3.4)
Time spent outside at
dusk or dawn on a
nonwork day (h) 3.1 (1.9) 2.2 (1.3)
Time total outside on
a nonwork day (h) 8.2 (4.5) 6.7 (3.4)
Personal behavior
Rarely or never avoid
areas where mosquitoes
are likely to be a
problem 30 (65) 685 (47)
Rarely or never avoid
going outdoors 43 (93) 1,190 (82)
Rarely or never wear
long sleeves or long
pants when outdoors 30 (65) 715 (49)
Rarely or never wear
mosquito repellent when
outdoors [greater than
or equal to]30 min 31 (67) 944 (65)
Practice [greater than or
equal to]2 personal
protective behavior
traits([dagger]) 19 (41) 894 (61)
Source-reduction behavior
Drain objects that may
collect water 13 (28) 457 (31)
Check and clean gutters 29 (63) 1,009 (69)
Use bug lamps/bug zappers 7 (15) 132 (9)
Practice >2
source-reduction
behavior traits 30 (65) 1,044 (72)
Characteristic OR (95% CI), p value
Indoor exposures
Open deck or unscreened
porch on home 2.36 (0.99-6.9), 0.04
Tears in screens 1.14 (0.55-2.32), 0.69
Mosquitoes in home
[greater than or
equal to]1x/wk 1.01 (0.46-2.14), 0.98
Outdoor exposures
Time outside at dusk or
dawn on work day (h) 1.32 ([dagger]) (1.09-1.58), 0.004
Total time outside on
a work day (h) 1.08 ([dagger]) (1.00-1.16), 0.066
Time spent outside at
dusk or dawn on a
nonwork day (h) 1.48 ([dagger]) (1.23-1.78), 0.001
Time total outside on
a nonwork day (h) 1.13 ([dagger]) (1.04 to 1.22), 0.003
Personal behavior
Rarely or never avoid
areas where mosquitoes
are likely to be a
problem 2.11 (1.10-4.08), 0.015
Rarely or never avoid
going outdoors 3.2 (1.01-16.20), 0.041
Rarely or never wear
long sleeves or long
pants when outdoors 1.94 (1.01-3.76), 0.031
Rarely or never wear
mosquito repellent when
outdoors [greater than
or equal to]30 min 1.12 (0.58-2.19), 0.73
Practice [greater than or
equal to]2 personal
protective behavior
traits([dagger]) 0.44 (0.23-0.83), 0.005
Source-reduction behavior
Drain objects that may
collect water 0.86 (0.43-1.71), 0.65
Check and clean gutters 0.75 (0.40-1.45), 0.36
Use bug lamps/bug zappers 1.80 (0.67-4.17), 0.156
Practice >2
source-reduction
behavior traits 0.74 (0.38-1.43), 0.33
* OR, odds ratio; CI, confidence interval.
([dagger]) Odds of WNV infection per hour spent outdoors.
([DAGGER]) Avoiding mosquitoes, wearing long sleeves and long pants,
using mosquito repellent.
|
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion