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Risk factors
By Mayo Clinic staffYour overall risk of getting West Nile virus depends on these factors:
- Time of year. The majority of cases in the United States have occurred between the months of July and September.
- Geographic region. West Nile virus has been reported in most of the United States but the Western and Midwestern states have had the highest incidence rates.
- Time spent outside. If you work or spend time outdoors, you have a greater chance of being bitten by an infected mosquito.
Risk of serious infection
Even if you are infected, your risk of developing a serious West Nile virus-related illness is extremely small — less than 1 percent of people who are bitten become severely ill. And most people who do become sick recover fully. You're more likely to develop a severe or fatal infection based on:
- Age. Adults over the age of 50 are at higher risk of infection.
- Health. Those who have a weakened immune system, such as from receiving an organ transplant, are at greater risk of infection.
- West Nile virus: Clinical description. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/clinicians/clindesc.htm. Accessed May 19, 2010.
- West Nile virus: Epidemiologic information for clinicians. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/clinicians/epi.htm. Accessed May 19, 2010.
- West Nile virus: Fact sheet. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/resources/WNV_factsheet.pdf. Accessed May 19, 2010.
- Lindsey NP, et al. Surveillance for human West Nile virus disease - United States, 1999-2008. Morbidity and Mortality Weekly Report. 2010;59:1.
- Questions and answers: Symptoms of West Nile virus. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/qa/symptoms.htm. Accessed May 20, 2010.
- Petersen LR. Epidemiology and pathogenesis of West Nile virus infection. http://www.uptodate.com/home/index.html. Accessed May 26, 2010.
- Petersen LR. Clinical manifestations and diagnosis of West Nile virus infection. http://www.uptodate.com/home/index.html. Accessed May 26, 2010.
- Petersen LR. Treatment and prevention of West Nile virus infection. http://www.uptodate.com/home/index.html. Accessed May 26, 2010.
- Questions and answers: Prevention. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/qa/prevention.htm. Accessed May 20, 2010.
- What you need to know about mosquito repellent. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/mosquitorepellent.htm. Accessed May 19, 2010.
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