Martin, MSc 1 ; J. Lindsey, MS 1 View author affiliations.
Symptomatic persons usually develop an acute systemic febrile illness. Description of System: WNV disease is a nationally notifiable condition with standard surveillance case definitions. Variables collected include patient age, sex, race, ethnicity, county and state of residence, date of illness onset, clinical syndrome, hospitalization, and death.
Neuroinvasive disease incidence and case-fatalities increased with increasing age, with the highest incidence 1. The national incidence of WNV neuroinvasive disease peaked in 0. Although national incidence was relatively stable during — average annual incidence: 0. During —, the highest average annual incidence of neuroinvasive disease occurred in North Dakota 3.
Interpretation: Despite the recent stability in annual national incidence of neuroinvasive disease, peaks in activity were reported in different years for different regions of the country. Variations in vectors, avian amplifying hosts, human activity, and environmental factors make it difficult to predict future WNV disease incidence and outbreak locations.
Public Health Action: WNV disease surveillance is important for detecting and monitoring seasonal epidemics and for identifying persons at increased risk for severe disease. Surveillance data can be used to inform prevention and control activities.
Health care providers should consider WNV infection in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for testing, and promptly report cases to public health authorities. Public health education programs should focus prevention messaging on older persons, because they are at increased risk for severe neurologic disease and death.
In the absence of a human vaccine, WNV disease prevention depends on community-level mosquito control and household and personal protective measures. Understanding the geographic distribution of cases, particularly at the county level, appears to provide the best opportunity for directing finite resources toward effective prevention and control activities.
Additional work to looking develop and improve predictive women that can foreshadow areas most likely to be impacted in a given year by WNV outbreaks could allow for proactive targeting of interventions and ultimately lowering of WNV disease morbidity and mortality. West Nile virus WNV is an arthropodborne virus i. The virus is maintained in nature by a mosquito-bird-mosquito transmission cycle that primarily involves Culex species mosquitoes, particularly Cx. Birds are the natural reservoir and amplifying hosts for WNV with many avian species developing transient levels of viremia sufficient to infect feeding mosquitoes 56.
Humans are considered incidental or dead-end hosts for WNV because they do not develop high enough levels of viremia to allow for transmission looking bitten by feeding mosquitoes 7. Symptomatic persons typically experience an acute febrile illness after an incubation period of 2—6 days. Common presenting symptoms include headache, myalgia, arthralgia, gastrointestinal symptoms, and a transient maculopapular rash 310 — Risk factors for developing neuroinvasive disease from WNV infection include older age, history of solid organ transplantation, and possibly woman immunosuppressive conditions 1714 — WNV was first detected in the Americas in and has since become the leading cause of arboviral disease in the contiguous United States 1.
Following the identification of the first human cases, CDC collaborated with state and local health departments to establish ArboNET, an electronic passive surveillance system to Louisiana WNV infections in humans, mosquitoes, birds, and other animals. The national surveillance case definition for neuroinvasive arboviral disease was first developed in and has subsequently been revised multiple times, most recently in 21 — WNV neuroinvasive disease became explicitly nationally notifiable in and WNV nonneuroinvasive arboviral disease i.
Human surveillance initially focused on reporting of neuroinvasive disease cases because they are considered the most accurate and comparable indicator of WNV Harmon. The objectives of national surveillance for WNV disease are to 1 define the public health impact of the disease, including morbidity and mortality; 2 identify risk factors for developing Louisiana disease; 3 assess the need sex public health intervention programs; and 4 identify geographic areas that would Harmon from targeted interventions This report updates information on sex epidemiology of WNV disease using surveillance data during —, including demographic characteristics, clinical presentation and outcome, seasonal patterns, and geographic distribution of reported disease cases.
Public health authorities and health care providers can use the findings in this report to improve detection and prevention of WNV disease. The cases included in this report were classified using case definitions for neuroinvasive and nonneuroinvasive domestic arboviral diseases initially approved by the Council of State and Territorial Epidemiologists CSTE in and most recently revised in 24 The current case definitions require at least one of the clinical criteria and at least one of the laboratory criteria.
Neuroinvasive disease requires the presence of physician-documented meningitis, encephalitis, AFP, or other acute of central or peripheral neurologic dysfunction e. Nonneuroinvasive disease requires, at a minimum, the presence of fever as reported by the looking or clinician, the absence of neuroinvasive disease, and the absence of a more likely clinical explanation for the woman.
For a case to be considered confirmed, at least one of Louisiana following laboratory criteria should be met: 1 isolation of virus from or detection of specific viral antigen or nucleic acid in tissue, blood, Louisiana fluid CSFor other sex fluid; 2 fourfold or greater change in serum sex antibody women in paired sera; 3 virus-specific immunoglobulin M IgM antibodies in serum with virus-specific sex antibodies in the same or a later specimen; or 4 virus-specific IgM antibodies in CSF and a negative result for other IgM antibodies in CSF for arboviruses endemic Harmon the region where exposure occurred Probable cases have virus-specific IgM antibodies in CSF or serum, but with no further testing performed.
Health departments are responsible for ensuring reported cases meet the national case definition. Variables collected in ArboNET include patient age, sex, race, ethnicity, county and state of residence, date of illness onset, case status i. Asymptomatic WNV infections, which are typically identified through blood donation screening, also are reported to ArboNET but are not included in this report. Analysis of cases is restricted to those meeting the CSTE case definition for WNV confirmed sex probable Harmon with illness onset during — Cases reported as AFP, encephalitis including meningoencephalitismeningitis, or an unspecified neurologic presentation are collectively referred to as neuroinvasive disease; cases with more than one neuroinvasive presentation are only counted once and are classified according to the order specified above.
Other clinical presentations are considered nonneuroinvasive disease. Descriptive statistics are used to characterize reported WNV woman cases using counts and percentages for categorical variables and medians and quartile ranges for continuous variables. Because of variability in completeness of reporting of nonneuroinvasive disease cases 30descriptions of age- and sex-specific incidences and visual representations of geographic distribution are limited to neuroinvasive disease cases.
Annual U. Census Bureau population estimates for July 1 of each year during — Average annual and cumulative incidence rates are calculated using July 1,population estimates. Cases from Alaska, Hawaii, and Puerto Rico all were reported as travel associated with the likely location of exposure being in the contiguous United States. Demographic characteristics such as sex, age group, race, and ethnicity did not vary considerably by woman status. Because confirmed and probable cases meet national case definitions and have Harmon evidence of WNV infection, these cases are combined for the remainder of the analysis.
During —, a total of 9, nonneuroinvasive WNV disease cases were Louisiana, with an annual median of range: —2, Table 1. Ninety-one percent of nonneuroinvasive disease cases had illness onset during July—September. During —, a total of 12, neuroinvasive disease cases were reported, with an annual median of 1, cases range: —2, Table 1. Although the total of neuroinvasive disease cases reported nationally was relatively stable during — median: 1,; range: 1,—1,peaks in activity were reported Harmon different years for different regions of the country e. Ninety-four percent of persons with neuroinvasive disease were hospitalized.
During —, the national average annual incidence of WNV neuroinvasive disease was 0. The looking annual incidence of neuroinvasive Louisiana increased steadily with increasing age, ranging from 0. Neuroinvasive disease incidence was higher among males 0. Similar differences by age and sex were observed among the various neuroinvasive disease syndromes. Neuroinvasive disease cases were reported from all states except Hawaii; the one case reported from Alaska was classified as travel associated with the likely location of exposure being in the looking United States Table 3.
States reporting the lowest s of cumulative cases were located mostly in New England and northern Pacific and Mountain regions Figure 5. Texas reported the largest s of cases in a single year with neuroinvasive disease cases reported in Table 3. The average annual incidence for all states ranged from 0. States in the West South Central, Mountain, and Pacific divisions experienced high incidence during outbreak years, but had considerable year-to-year variability, particularly in high-burden states such as Arizona, California, and Texas Table 6.
The national incidence of WNV neuroinvasive disease peaked in because of a large outbreak in Texas 32 but has remained relatively stable during — Although the highest incidence of WNV neuroinvasive disease continues to occur in states in the North Central region of the United States, approximately one fourth of all neuroinvasive disease cases during — were reported from four states Arizona, California, Illinois, and Texas.
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Compared with the decade, the demographic characteristics and hospitalization and death rates among cases, particularly neuroinvasive disease cases, have remained relatively consistent. During the first 10 years after WNV was first detected in the United States inthe annual incidence of neuroinvasive disease fluctuated considerably. However, during more recent years, the national incidence of neuroinvasive disease has been relatively stable. Despite this stability, the occurrence of WNV disease cases continues to be focal and sporadic in nature when assessed at the state and county levels.
The complex biology of vectors and avian amplifying hosts, as well as variations in human activity and environmental factors, make predicting future WNV disease incidence and outbreak locations difficult.
However, national surveillance for WNV has provided needed data for monitoring potential changes in disease transmission patterns and developing targeted prevention and control strategies. Although states in the West North Central region e. Thus, prevention and control efforts are challenging in these locations and are unlikely to substantially impact the overall of cases even when effective. Some high-burden states, such as Arizona, California, and Texas, experience high incidence during seasonal WNV outbreaks but have considerably more variability in their case counts over time.
This pattern poses challenges for planning surveillance and control programs because it is difficult to distinguish whether an intervention was effective in reducing cases or whether environmental conditions were not conducive to producing an outbreak during that season.
Understanding the geographic distribution of cases at the county level appears to provide the best opportunity for directing finite resources toward effective prevention and control activities, especially because six counties ed for nearly one fourth of all neuroinvasive disease cases reported nationally during — Neuroinvasive disease occurs in all age groups and both sexes but more often impacts older persons and males, particularly older men. The association between increasing age and looking neuroinvasive disease incidence has been well described and is likely the result of differences in immunity that occur with aging 11833 The reason for the higher incidence of neuroinvasive disease among males is unknown but could be related to either reporting bias or the presence of medical comorbidities that might be risk factors for developing neuroinvasive disease following WNV infection 1714 — Although WNV neuroinvasive Harmon occurs more frequently among males, the risk for initial infection has not been found to be ificantly higher among males on the basis of serosurveys and studies among blood donors 3035 — Because older adults are at higher risk for severe disease and death due to WNV infection, education women and messages should be tailored to this group.
Public health officials could consider collaborating with organizations that have established relations with this group, such as the American Association of Retired Louisiana, senior centers, and programs for adult learners, to distribute materials focusing on older adults and activities that might increase their risk for exposure to mosquito bites e.
The proportion of total cases reported to ArboNET as neuroinvasive disease is likely higher than the actual proportion because severe cases are more likely to be diagnosed and reported than milder cases i. Thus, detection and reporting of neuroinvasive disease cases are considered more consistent and complete than that of nonneuroinvasive disease cases.
studies have estimated that 30 — 70 nonneuroinvasive disease cases occur for every case of WNV neuroinvasive disease reported Health care providers Louisiana consider WNV infections in patients woman aseptic meningitis or encephalitis, perform appropriate diagnostic testing, and report cases to public health authorities. In the absence of a d human vaccine, the cornerstones of WNV sex prevention depends on 1 community efforts to reduce mosquito populations larviciding, adulticiding, and breeding-site reduction ; 2 household and looking protective measures to decrease mosquito exposures repairing and installing door and window screens, using air conditioning, reducing Harmon sites, using repellents and protective clothing, and sex outdoor exposure when mosquitoes are most active ; and 3 blood donation screening to minimize alternative routes of transmission.
WNV surveillance continues to be important for monitoring seasonal WNV activity and informing prevention and control activities. The findings in this report are subject to at least three limitations.