Descriptive epidemiology and west nile virus
Objectives:
• Follow and comprehend a scenario using epidemiologic principles.
• Identify and describe key descriptive epidemiology indicators such as person, place, and time.
• Describe some patterns of disease according to person, place, and time.
• Create graphs or tables as appropriate to further describe disease information.
Assignment (10 points)
Read the following scenario and answer the corresponding questions to the best of your ability. For equation questions, please show your work. For multiple choice or true/false questions, please choose the best answer. For short-answer questions, please do your best to answer all parts of the question, but alsoconsider the length of your answerand try to be brief. Be sure to check your work, and show evidence for your answers when necessary.
Introduction
West Nile virus (WNV) is a vector-borne disease (zoonotic arbovirus, Flavivirus), transmitted by WNV infected mosquitoes (Mayo Clinic, 2012). These mosquitoes become infected when they feed on infected animals-most likely birds-and then transmit the infection to humans or animals (CDC, 2012). West Nile virus is endemic to East Africa, particularly the Western Nile region of Uganda, but was first identified in the United States in 1999 in Queens, New York. West Nile Virus is often found in ecosystems where mosquitoes thrive and breed (low to medium altitudes, access to water and standing water, tropical/temperate/seasonal climates, dense brush to some flora).
West Nile virus can present symptoms such as fever, headaches, fatigue, muscle pain, aches, malaise, nausea, anorexia, vomiting, myalgias and rash-although about 80% of cases will not show any detectable symptoms at all-and less than 1% of cases will result in severe neurological disease, affecting the central nervous system with inflammation of the brain (encephalitis or meningitis). People with compromised immune systems are more likely to develop a more severe or symptomatic version of the disease.Symptoms can develop after an incubation period of 2 to 15 days from the time of infection (CDC, 2012).
In 2012, the United States experienced 5,674 confirmed cases and 286 deaths-a mortality rate of 5% of reported cases. Of the 5,674 cases, 2,873 had neuroinvasive disease from West Nile (presumably the 50% rate of neuroinvasive disease was so high because of under-reporting of asymptomatic WNV).
In the state of Texas in 2012, there were 1,700 confirmed and probable cases of WNV, and 89 deaths. There were 780 neuroinvasive disease cases.
Questions
This is a table of the confirmed cases from the Texas Department of State Health Services.
(Texas DSHS, 2013)
Question 1 (1 point):From the above table, please identify the person data provided as a major indicator (as described in the descriptive epidemiology readings and lecture). Review the person data in the table and make an assertion about who is being affected the most by or the most at risk for developing WNV and WNV Fever vs. WNV neuroinvasive disease.
Answer:
The following maps show West Nile Summary of activity by counties within Texas, West Nile Fever presence in Texan counties, and West Nile neuroinvasivedisease presence within Texan counties respectively (Texas DSHS, 2013).
Question 2 (1 point):From the above graphs, please identify the place data provided as a major indicator (as described in the descriptive epidemiology readings and lecture). Review the place data in the graphs and make an assertion about which areas are being affected the most by or the most at risk for developing WNV and WNV Fever vs. WNV neuroinvasive disease and which areas are not being affected. If you know anything about the general geography or topography of Texas, please include this (e.g. altitude, desert, woods, swamp, climate) and the interaction place would have on the vector (mosquitoes).
Answer:
(Texas DSHS, 2013)
Question 3 (1 point):From the above graph, please identify the time data provided as a major indicator (as described in the descriptive epidemiology readings and lecture). Review the time data in the graph and make an assertion about whenpeople are being affected the most by or the most at risk for developing WNV and when they are not being affected as much.
Answer:
Question 4 (1 point):
As you have seen so far, epidemiologists generally collect a lot of information about cases and suspected cases. From the following list of demographic person/place/time indicators, please list the five indicators you believe to be most important when discussing risk from WNV. For each of the indicators you choose, please give a sentence or two justifying why it is important to collect such data concerning WNV.
Seasons Climate Age
Neighborhood Gender Birthplace
Months Rural/Urban Annual income
Recent travel Leisure activities Weeks
Race Occupation Country
Time of day School district Marital status
Answer:
Question 5 (1 point):Draw a table from the following information:
• United States
• Suspected Human WNV Cases: 25
• CDC Statistics, Surveillance, and Control, 2011
• Confirmed Human WNV Fever Cases: 322
• Encephalitis/Meningitis WNV Cases: 373
• Year 2009
• Confirmed Human WNV Deaths: 32
Be sure to review and include the characteristics of a good table.
Answer:
Question 6 (1 point):Interpret the table you drew above into words.
Answer:
Question 7 (1 point):
Draw a graph from the following information:
• CDC, Disease Maps 2013
• Number of States with Human WNV, confirmed
o 2010: 41
o 2011: 44
o 2012: 50
• Number of States with Mosquito WNV, confirmed
o 2010: 43
o 2011: 38
o 2012: 50
• Number of States with Bird WNV, confirmed
o 2010: 20
o 2011: 18
o 2012: 28
Be sure to review and include the characteristics of a good graph.
Answer:
Question 8 (1 point):Interpret the graph you drew above into words.
Answer:
Question 9 (2 points):Vaccines for WNV are not yet available, but epidemiologists have been gathering information on the spread of WNV via surveillance from CDC called ArboNet. This information should hopefully lead to more concrete guidelines on how to prevent contracting the disease and lessen itsimpact of it on victims. Synthesize the information you know from this case study to write five recommendations for the public to follow to prevent contracting WNV or lessen the morbidity of WNV cases. You can use the information you know about risk factors and determinants to help guide your recommendations.
