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Short Note 1
Sero-surveillance in Delhi, India – An Early Warning Signal for Timely
Detection of Dengue Outbreaks
D.
Bhattacharya*, Veena Mittal*#, M. Bhardwaj*, Mala Chhabra*,
R.L. Ichhpujani** and Shiv Lal*
*National Institute of Communicable
Diseases, 22-Sham Nath Marg, Delhi
– 110 054, India
**Directorate General of Health Services, Nirman Bhavan, New Delhi – 110 011, India
In India the
first major outbreak of dengue fever (DF) accompanied with dengue
haemorrhagic fever (DHF) was reported in Kolkata (Calcutta)
in 1963[1]. More than 60 outbreaks have been reported since
1956 to date[2].
Of these two major outbreaks of DF/DHF occurred in 1996 and 2003 in Delhi
and its adjoining states. Surveillance is the most cost-effective approach
for prevention and control of dengue. A
strong surveillance system will help in detecting early warning signals of an
outbreak, instituting timely and appropriate control measures, assessing the
impact of intervention measures and early containment of the outbreak.
Considering the above facts, the arbovirus laboratory at the National
Institute of Communicable Diseases, Delhi, has started sero-surveillance and monitoring
of dengue fever in Delhi
since 1996 as an ongoing activity. It was intended to develop an early
warning signal for timely detection of an impending outbreak and institution
of preventive and control measures in high-risk areas.
Sera samples of clinically suspected cases of DF and/or DHF are received from
various hospitals of Delhi round
the year. These samples were tested for dengue by haemagglutination
inhibition (HI) test[3]
or IgM Capture ELISA Test[4]. A titre of ³ 1:1280
in HI test in acute phase serum is considered a presumptive diagnosis of a
current dengue infection[5].
Samples positive for IgM antibodies against dengue virus indicate recent
infection with dengue virus.
The results of the sentinel sero-surveillance from 1996 to 2003 are
summarized in the Table. The analysis of data over the period of eight years
shows that dengue strikes Delhi
every year. The positivity ranges from approximately 13%-33%, except in 1996
and 2003 when dengue fever occurred in epidemic proportions along with DHF.
The positivity in these two years was 53.4% and 57.8% respectively.
The month-wise distribution of samples tested from 1996-2003 shows that the positivity
for dengue starts appearing in the month of August and reaches a peak in
October and continues till mid-November and then a decline starts and the
last cases are reported upto 2nd week of December. The data for
2003 also shows a similar trend (Figure).
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Table: Dengue serology during
the years 1996 – 2003 in Delhi
|
2003
|
+ve
|
0
|
0
|
0
|
0
|
0
|
5
|
0
|
16
|
433
|
1,438
|
450
|
14
|
2,356
(57.8%)
|
|
Tested
|
7
|
5
|
13
|
8
|
10
|
11
|
11
|
43
|
701
|
2,351
|
877
|
35
|
4,072
|
|
2002
|
+ve
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
12
|
18
|
11
|
42
(12.8%)
|
|
Tested
|
18
|
19
|
19
|
34
|
6
|
12
|
23
|
17
|
31
|
55
|
60
|
34
|
328
|
|
2001
|
+ve
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
6
|
44
|
129
|
94
|
9
|
283
(33.2%)
|
|
Tested
|
19
|
21
|
11
|
10
|
13
|
22
|
22
|
43
|
127
|
304
|
225
|
35
|
852
|
|
2000
|
+ve
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
13
|
74
|
112
|
13
|
213
(30.6%)
|
|
Tested
|
11
|
8
|
9
|
8
|
26
|
9
|
18
|
32
|
56
|
188
|
254
|
77
|
696
|
|
1999
|
+ve
|
0
|
0
|
0
|
0
|
1
|
0
|
0
|
0
|
17
|
35
|
35
|
5
|
93
(19.2%)
|
|
Tested
|
5
|
11
|
12
|
7
|
11
|
12
|
11
|
27
|
71
|
145
|
130
|
40
|
482
|
|
1998
|
+ve
|
1
|
0
|
0
|
0
|
0
|
0
|
1
|
0
|
5
|
38
|
140
|
21
|
206
(23.7%)
|
|
Tested
|
21
|
11
|
24
|
28
|
67
|
27
|
31
|
48
|
70
|
201
|
293
|
47
|
868
|
|
1997
|
+ve
|
0
|
0
|
0
|
1
|
0
|
0
|
0
|
3
|
65
|
159
|
26
|
1
|
255
(33.3%)
|
|
Tested
|
5
|
6
|
4
|
39
|
33
|
8
|
15
|
20
|
169
|
369
|
81
|
15
|
764
|
|
1996
|
+ve
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
73
|
343
|
74
|
3
|
493
(53.4%)
|
|
Tested
|
1
|
4
|
3
|
0
|
3
|
0
|
0
|
3
|
159
|
643
|
104
|
11
|
931
|
|
Year/
Month
|
JAN
|
FEB
|
MAR
|
APR
|
MAY
|
JUN
|
JUL
|
AUG
|
SEP
|
OCT
|
NOV
|
DEC
|
Total
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Figure. Month-wise samples tested/positive for dengue
antibodies in Delhi during
the year 2003
The studies for the estimation of the House Index (HI) of mosquitoes also
shows that the house index for Aedes aegypti, the vector of dengue
fever, starts building-up during the rainy season, i.e. from July and reaches
a peak in August-September[6].
A regular monitoring of suspected dengue cases by detection of IgM antibodies
to dengue virus can act as an early warning signal for an impending outbreak.
The above observations show that serological surveillance throughout the
year, especially during the outbreak-prone period, can play an important role
in the detection of early cases.
References
1. Ramakrishnan
SP, Gelfand HM, Bose PN, Sehgal PN and Mukherjee RN. The epidemic of acute
haemorrhagic fever, Calcutta. Ind
J Med Res, 1964, 52: 633-650.
2. Epidemic
preparedness – dengue fever, DHF and DSS. CD Alert, Monthly Newsletter,
National Institute of Communicable Diseases, Delhi,
June 2001, Volume 5 (16).
3. Clark
DH and Casals J. Techniques for haemagglutination and haemagglutination
inhibition with arthropod borne viruses. Am J Trop Med, 1958, 7: 561-573
4. Lam
SK, Devi S and Pang T. Detection of specific IgM dengue infection. Southeast
Asian J Trop Med Public Health, 1987, 18: 532-538.
5. Gubler
DJ. Serological diagnosis of dengue/dengue haemorrhagic fever. Dengue
Bulletin, 1996, 20: 20-23.
6. Katyal
R, Singh K and Kumar K. Seasonal variation in Aedes aegypti population
in Delhi, India, Dengue Bulletin, 1996, 20: 78-81.
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