Case study: Analyzing malaria surveillance data in Darjeeling
IDSP 2 week course version – 14 January 2008
Case study developed by the Master of Applied Epidemiology (MAE) - Field Epidemiology Training
Programme (FETP) from the National Institute of Epidemiology (NIE), Indian Council of Medical
Research (ICMR), Chennai, Tamilnadu, India. It is based upon a secondary data analysis conducted by Dr
Puran Kumar Sharma, FETP scholar, under the supervision of Dr R. Ramakrishnan.
Pre-requisite:
This case study was prepared to follow a lecture on surveillance data analysis. Participants will be
expected to be familiar with:
 Principles of public health surveillance;
 Data aggregation;
 Calculation of population-based incidence;
 Time, place and person analysis of epidemiological data.
Learning objectives
At the end of the case study, the participant will be able to:
1. Calculate population-based incidences;
2. Prepare a curve of incidence over time (“TIME analysis”);
3. Draw a map of incidence by geographical area (“PLACE analysis”);
4. Analyze surveillance according to personal characteristics (“PERSON analysis”);
5. Propose recommendations on the basis of surveillance data.
Using this case study in a class
This is designed as a stand-alone case study and does not come with a facilitator’s guide. The answers to
all the questions in each section are provided as an introduction to the following section. To run this case
study in a class, it is proposed to distribute it one part at a time. Participants take turns reading it out loud,
paragraph by paragraph. Reading everything out loud and in turns has two advantages. First, everyone
can quickly participate and go beyond the inhibition of having her/his voice heard in a large room.
Second, time is given to the whole class to understand the issue and think about the answers. The
participant reading the question may try to answer it if s/he can propose an answer. Otherwise, the matter
is discussed as a group. The next participant reads the next question and so on until the end of the page.
After distributing the next part, participants continue reading the text inn that manner until the case study
is over. Once the epilogue has been read, it is proposed to go back to the first page to read the objectives
again. This re-iterates the learning and provides additional clarification opportunities.
Part 1. Malaria in Darjeeling
The main components of the national Indian malaria programme are (1) early case detection and
treatment, (2) vector control through use of insecticide (DDT) and use of larvivorous fishes and (3)
promotion of personal protection methods, including insecticide-impregnated mosquito nets.
West Bengal accounts for six percents of the total number of malaria cases reported annually in India.
During the same year, in the West Bengal district of Darjeeling, the caseload was on the rise and most
cases were caused by Plasmodium falciparum. In the district, three “blocks” -Kurseong, Gorubathan and
Naxalbari-Matigara- out of 10 were endemic for malaria. Chloroquine resistance is prevalent in the area.
The Kurseong block covers plain areas, hilly areas and foothills with dense forests and plenty of water
bodies. While public health decision makers would have liked to focus more attention on malaria, they
lacked evidence to guide their action. Thus, an epidemiologist assigned to the district decided to analyze
routine surveillance data to guide the control programme.
A case of malaria was defined as the occurrence of fever with a blood slide positive for malaria. The
epidemiologist reviewed the monthly and annual reports and other records/reports on malaria. The
epidemiologist aggregated the cases by year and the cases by month (Table 1).
Question 1
What key additional piece of information is needed to analyze the data provided in Table 1?
Malaria in Darjeeling – 14 January 2008
2
Table 1: Reported cases of malaria by month, 2000-2004, Kurseong block, Darjeeling district, West Bengal, India, 2000-2004.
Month
January
February
March
April
May
June
July
August
September
October
November
December
Year
2000
P. falc.
Total
4
8
3
4
4
6
8
11
9
14
16
21
26
41
6
10
6
12
8
17
7
12
4
8
101
164
Malaria in Darjeeling – 14 January 2008
2001
P. falc.
Total
10
16
11
18
12
21
4
8
11
22
9
18
23
31
21
44
25
32
16
23
16
31
17
29
175
293
2002
P. falc.
Total
10
17
6
12
10
16
3
4
4
10
26
44
39
64
29
51
36
54
22
32
19
24
15
31
219
359
2003
P. falc.
Total
6
34
10
18
3
13
1
5
8
29
54
62
27
99
96
191
116
173
72
137
80
206
117
245
590
1212
2004
P. falc.
Total
19
32
6
13
29
29
17
19
41
50
11
34
24
30
12
46
110
136
111
126
76
95
83
87
539
697
2001-2004
P. falc.
Total
49
107
36
65
58
85
33
47
73
125
116
179
139
265
164
342
293
407
229
335
198
368
236
400
1,624
2,725
Part 2. Obtaining population denominators
The epidemiologist decided to use 2001 census data obtained from the office of the Block
Development Officer, Kurseong. He obtained the population sizes by sub-centre (Table 2). He
projected these population figures backwards for 2000 and forward for 2002-2004 using the annual
the population growth rate (2.04%). He applied the age and sex distribution of the state (Table 3) to
the block as this information was not available at this level.
Table 2: Population of the Kurseong block by sub-centre, 2001 census, Darjeeling district,
West Bengal, India (Total: 83,793)
Sub-centre
Ambootia
Bagora
Chimney
Chunbhatti
Dilaram
Dudhia
Ghaletar
Ghayabari
Giddapahar
Kharey
Lanku
Latpanchar
2001 Population
3,000
1,697
3,436
2,958
4,185
6,786
5,815
3,282
3,309
2,847
2,065
2,442
Sub-centre
Mahanadi
Makaibari
Malootar
Pankhabari
Rajbari
Rinchingtong
Rohini
Shankarniwas
Singell
St. Mary's
Sukna
Turuk
2001 Population
3,830
3,165
1,970
4,615
3,070
2,438
4,197
2,587
2,435
2,883
8,123
2,658
Table 3: Age and sex distribution of the population of West Bengal, India, 2001
Population group
Male
Female
Male < 5 yr
5-14 yr
15-49 yr
> 49 yr
< 5 yr
5-14 yr
15-49 yr
> 49 yr
Relative proportion
5.8%
12.8%
26.8%
6.7%
5.7%
12.3%
23.9%
6.0%
The projection of the 2001 population size generated population size estimates of 82,118 for 2000
(projection one year back) and 85,502, 87,247 and 89,026 for 2002 to 2004 respectively.
Question 2
Analyze the data to represent the trend between 2000 and 2004 and the seasonality.
Malaria in Darjeeling – 14 January 2008
Part 3. Geographical distribution
The analysis of the annual incidence over the years suggested an increase between 2000 and 2004
(Figure 1) while the monthly incidence averaged over five years (seasonality) indicated a
predominance of malaria during the second part of the year (Figure 2).
Figure 1: Incidence of malaria in Kurseong block, Darjeeling district, West Bengal, 20002004.
1600
1400
Falciparum
Annual incidence per 100,000
1200
Malaria
1000
800
600
400
200
0
2000
2001
2002
2003
2004
Year
Figure 2: Monthly incidence of malaria (averaged over five years) in Kurseong block,
Darjeeling district, West Bengal, 2000-2004.
Monthly incidence per 100,000 (averaged over five years)
100.0
90.0
Falciparum
80.0
Malaria
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Months
`
Malaria in Darjeeling – 14 January 2008
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At this stage, the epidemiologist is preparing the analysis by geographical area (sub-centres).
Table 4: Reported cases of malaria in Kurseong sub-centres, Darjeeling district, West Bengal,
India, 2000-2004 1
Sukna
Dudhia
Chunbhatti
Rohini
Ambootia
Ghayabari
Pankhabari
Malootar
Mahanadi
Rajbari
Singell
Makaibari
Total
2000
97
39
14
6
4
4
0
0
0
0
0
0
164
2001
174
68
24
7
7
10
3
0
0
0
0
0
293
Year
2002
210
87
41
8
8
5
0
0
0
0
0
0
359
2003
671
357
62
20
44
34
5
4
6
2
1
6
1212
2004
446
165
52
22
0
12
0
0
0
0
0
0
697
Total
1,598
716
193
63
63
65
8
4
6
2
1
6
2,725
Figure 3: Sub-centres of Kurseong block, Darjeeling district, West Bengal, India
Question 3
Analyze the data to represent the geographical distribution in the area.
1
Sub-centres sorted by decreasing order of reported cases.
Malaria in Darjeeling – 14 January 2008
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Part 4. Malaria among selected population groups
The distribution of the incidence of malaria in the Kurseong indicated that the Southern part of the
block is more affected (Figure 4). This part of the block is located in the plains and is characterized
by the proximity of forest and rivers, shown on the map.
Figure 4: Averaged yearly incidence of malaria in the sub-centres of Kurseong block,
Darjeeling district, West Bengal, India, 2000-2004
The epidemiologist is now preparing the analysis by age and sex.
Table 5: Distribution of malaria by age and sex, Kurseong district, Darjeeling district, West
Bengal, India, 2000-2004.
Year
2000
2001
2002
2003
2004
Total
0 to 4
10
15
27
109
43
204
Age groups (years)
5 to 14
15-49
57
90
88
176
92
215
300
577
159
263
696
1,321
> 49
7
14
25
226
232
504
Sex groups
Male
Female
96
68
132
161
204
155
661
551
355
342
1,448
1,277
Total
164
293
359
1212
697
2,725
Question 4
Analyze the data to describe the age and sex groups affected by malaria.
Malaria in Darjeeling – 14 January 2008
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Part 5. Conclusions and recommendations
The incidence of malaria by age and sex indicates that all age and sex groups are equally affected
(Table 6).
Table 6: Average incidence of malaria by age and sex, Kurseong block, Darjeeling District,
West Bengal, India, 2000-2004
Demographic characteristic
Age
Sex
< 5 yr
5-14 yr
15-49 yr
> 49 yr
Male
Female
Total
Cases
2002 Population 2
204
696
1,321
504
1,448
1,277
2,725
9,833
21,461
43,350
10,859
44,547
40,956
85,502
Averaged annual
incidence per 100,0003
415
649
609
928
650
624
637
Overall, the epidemiological data indicate that (1) malaria incidence has been increasing in
Kurseong between 2000 and 2004, with a higher incidence during the second part of the calendar
year, that (2) a number of sub-centres located close to forests and rivers are most affected and that
(3) incidences are high in all age and sex groups, suggesting unstable transmission and lack of
immunity. Overall, these findings may suggest a change in the epidemiology of malaria. A
juxtaposition of the changes in climatic parameters and malaria epidemiology features suggests that
the changes in the epidemiology of malaria in Kurseong could be a consequence of climatic
changes.
Question 5.A
What conclusions can be drawn from the analysis of the surveillance data?
Question 5.B
What recommendations may be proposed from the results of the analysis of the surveillance data?
2
3
Mid-time population during the 2000-2004 period
Divided by five to average the incidence over the five years (2000-2004).
Malaria in Darjeeling – 14 January 2008
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Part 6. Epilogue: Addressing the emergence of malaria in Darjeeling
The epidemiology of malaria is changing in the Kurseong block of Darjeeling district. There is an
increase of incidence that is probably caused by an increase of transmission. This phenomenon
occurs concurrently with an increase in the proportion of Plasmodium falciparum infections. This
increase of the proportion of Plasmodium falciparum may be attributable to the recommended use
of chloroquine to treat patients. Plasmodium falciparum is resistant to chloroquine in the area, thus,
the use of this medication selects this organism over Plasmodium vivax. The combination of
increasing incidence and high proportion of Plasmodium falciparum represents a real danger in
populations that have little immunity to malaria because of unstable transmission in the past.
Outbreaks leading to deaths are likely to occur.
On the basis of his analysis of the surveillance data, the epidemiologist recommended to:
1. Mobilize resources to strengthen the malaria control programme, particularly in the
geographical areas of highest incidence;
2. Increase the annual blood examination rate (that is under the recommended 10%) with more
emphasis on active case search;
3. Shift from chloroquine to a combination of Artesunate and Sulfadoxine-Pyrimethamine for
Plasmodium falciparum cases as the first line drug as per the WHO guidelines; i
4. Evaluate the malaria control programme to identify what could be done to better control the
disease.
References
i
WHO, 2001. The use of Antimalarial drugs. World Health Organisation, Geneva,
WHO/CDS/RMM/2001.35
Malaria in Darjeeling – 14 January 2008
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