Health surveillance in a country with limited resources
Context
The health authorities of CountryA have observed a considerable change in the health indicators recorded by health professionals in theterritory. Country A is an area which is known for a high spread of infectious agents, and morerecently it is experiencing a health crisis due to the number of cancer-related deaths. In 2020, they decideto set up an epidemiological surveillance unit to have a better vision of the state of health of thepopulation. You have been hired as an epidemiologist to coordinate the surveillance unit and respondto requests from local authorities.
Methods
You are asked to carry out twoepidemiological surveys. The first survey aims to measure the frequency of HIV infection among theinhabitants of 4 rural villages (308 inhabitants in total). The measurements carried out should allow localauthorities to know the frequency of people currently infected and to compare this frequency withthat of other populations abroad. The HIV status will be checked by a serological test. According topast surveys the expected frequency is around 10%. You have a maximum budget of $2,500 US and eachsubject included costs $10 US.
In addition, you must measure the annual frequency of canceroccurrence using the help of the national cancer registry which was set up in 2006.
Results
Table 1 gives the results from the first survey on HIVinfections.
Table1: Frequency of HIV positive serologies in September 2020 among the inhabitantsof 4 villages in Country A (n = 308).
Variable Category Nb HIV Mesure of
frequency(95% CI)
Place of residence
Village A6 13.6 (5.1-27.1)
Village B21 25.9 (16.8-36.9)
Village C34 35.8 (26.2-46.3)
Village D19 21.6 (13.5-31.7)
Sex
Men 1214.6 (7.8-24.1)
Women 6830.1 (24.2 -36.5)
Ethnicity
Blacks 5732.8 (25.8-40.3)
Other 2317.2 (11.28-24.6)
Age
18-40 36xx.x (xx-xx)
41-85 4422.0 (16.5-28.4)
Total 80 26.0 (21.1-30.9)
95% CI: 95% confidence intervalof the measure of frequency.
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The cancer registry has provided you with the numbers of newcancer cases by year and by ethnicorigin (Table 2). You also have census data for this period (“population”column).
Table 2: Annual cancer population by ethnic origin in Country Abetween 2006 and 2015 YearsCases of cancer Population
Total Black White Asian TotalBlack Other*
2006 22 7 11 4 3762 1254 2508
2007 10 3 5 2 7284 2428 4856
2008 19 6 9 4 9381 3127 6254
2009 16 5 8 3 3267 1089 2178
2010 17 5 9 3 4434 1478 2956
2011 6 2 3 1 5367 1789 3578
2012 19 6 9 4 7662 2554 5108
2013 22 7 11 4 9363 3121 6242
2014 13 4 6 3 6342 2114 4228
2015 16 5 8 3 4365 1455 2910
* : Whites and asians mixedtogether.
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Questions
Module 4: Infectious andCommunicable Disease Epidemiology: (10 marks)
1. Regarding Table 1, what is the study designused to meet the objective? Justify your answer.
2. What is the most appropriate measure of frequency for thisstudy? Calculate this frequency measurefor HIV among person between the ages of18 and 40and its 95% confidenceinterval.
3. Does the measure of HIV frequency among persons aged 18 to 40 differ significantlyfrom peopleaged 40 to 85? Justify your answer.
4. You incur unforeseen expenses related to data collection in thefield. So you are forced to include fewer subjects in your sample. What is(are) the consequence (s) on the resultsof your HIV study?
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Module 5:Chronic Non-Communicable Diseases Epidemiology (10 marks)
5. Regarding Table 2, what is the study designused to measure the annual frequency of cancers? Justify your answer.
6. Regarding the data on the newcases provided in Table 2:
a. Calculate the incidence ofcancer in Country A in 2006 for the entirepopulation.
b. Calculate the (crude) incidence rate observed during this10-year period among blacks. Use themost suitable method
7. The public health authoritiesof Country A would like to:
a) Compare the incidence of cancer between blacks and whitesin Country A. In your opinion, is it possible to provide theseindicators with the data you have? if not, what do you need to perform this calculation?
b) Compare the incidence of cancers between Country A and a secondcountry (Country B) which has an age structure which differs significantlyfromthat of Country A. Do you think that themethod used to estimate the incidence (crude rate) is appropriate? Justify your answer.
8. In addition to the two studies requested, the public healthauthorities have entrusted you with thefollowing missions:
b) Discover a new treatment forAIDS;
c) Findthe cause of clustered cases of nosocomial infections in a hospital; d) Measurethe effectiveness of an HPV vaccine in the population;
e) Know the annual number ofpremature births in Country A.
f) Know the causes of pulmonary oedema for a patient admitted tothe emergency room.
Identify the missions above forwhich epidemiology is NOT usedandjustify your answer.
