McHenry County Department of Health
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Health Statistics and Epidemiology

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Epidemiology is the study of the distribution of disease and factors affecting the health of populations with the goal of preventing disease and promoting health. At McHenry County, the epidemiologist’s primary role is to conduct disease surveillance, investigate and describe disease outbreaks, analyze data to determine risk factors for adverse health outcomes, and plan for and respond to public health emergencies.



West Nile VirusConfirmed Probable Cases of West Nile 2015 - 2018 YTD

West Nile is a virus most commonly spread to people by mosquito bites. In North America, cases of West Nile virus (WNV) occur during mosquito season, which starts in the summer and continues through fall. WNV cases have been reported in all of the continental United States. There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not have symptoms. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites (source: Centers for Disease Control and Prevention [CDC]).

Flu Vaccination Recommendations

The CDC has announced its vaccination recommendations for the 2018 - 2019 flu season. The CDC recommends:

  • Yearly flu vaccination for people 6 months and older.
  • Get vaccinated by the end of October.

Get more information on the 2018 - 2019 flu vaccination recommendations.