Positive WNV test results obtained via use of these kits should be confirmed by additional testing at a state health department laboratory or CDC.In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry, and virus culture of autopsy tissues can also be useful. Only a few state laboratories or other specialized laboratories, including those at CDC, are capable of doing this specialized testing. Differential diagnosis
A number of various diseases may present with symptoms similar to those caused by a clinical West Nile virus infection. Those causing neuroinvasive disease symptoms include the enterovirus infection and bacterial meningitis. Accounting for differential diagnoses is a crucial step in the definitive diagnosis of WNV infection. Consideration of a differential diagnosis is required when a patient presents with unexplained febrile illness, extreme headache, encephalitis or meningitis. Diagnostic and serologic laboratory testing using polymerase chain reaction (PCR) testing and viral culture of CSF to identify the specific pathogen causing the symptoms, is the only currently available means of differentiating between causes of encephalitis and meningitis. Prevention
Many of the guidelines for preventing occupational West Nile virus exposure are common to all mosquito-borne diseases.Public health measures include taking steps to reduce mosquito populations. Personal recommendations are to reduce the likelihood of being bitten. General measures to avoid bites include:

Using insect repellent on exposed skin to repel mosquitoes. Repellents include products containing DEET and picaridin. DEET concentrations of 30% to 50% are effective for several hours. Picaridin, available at 7% and 15% concentrations, needs more frequent application.
For neuroinvasive disease the additional risk factors include older age (>50+), male sex, hypertension, and diabetes mellitus.A genetic factor also appears to increase susceptibility to West Nile disease. A mutation of the gene CCR5 gives some protection against HIV but leads to more serious complications of WNV infection. Carriers of two mutated copies of CCR5 made up 4.0 to 4.5% of a sample of people with West Nile disease, while the incidence of the gene in the general population is only 1.0%.The most at risk occupations in the U.S. are outdoor workers, for example farmers, loggers, landscapers/groundskeepers, construction workers, painters, summer camp workers and pavers. Two reports of accidental exposure by laboratory personnel working with infected fluids or tissues have been received. While this appears to be a rare occurrence, it highlights the need for proper handling of infected materials. The World Health Organization states that there are no known cases of health care workers acquiring the virus from infected patients when the appropriate infection control precautions are observed. Diagnosis
Preliminary diagnosis is often based on the patients clinical symptoms, places and dates of travel (if patient is from a nonendemic country or area), activities, and epidemiologic history of the location where infection occurred. A recent history of mosquito bites and an acute febrile illness associated with neurologic signs and symptoms should cause clinical suspicion of WNV.Diagnosis of West Nile virus infections is generally accomplished by serologic testing of blood serum or cerebrospinal fluid (CSF), which is obtained via a lumbar puncture.