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Retrospective Analysis of Three Years Surveillance Data of Dengue Fever in Karachi.

Byline: Mohammed Shakeel Aamir Mullick and Sultana Habibullah


Dengue fever is an acute viral infection transmitted to humans by the bite of female mosquito Aedes aegypti. There are four serotypes; DENV-1, DENV-2, DENV-3, and DENV-4. Each serotype presents with fever and severe flu like illness and sometimes with dengue haemorrhagic fever (DHF)1. Fever is the main presentation, while complications include dengue haemorrhagic fever and dengue shock syndrome. Recovery from infection by one serotype provides lifelong immunity against that particular serotype but confers only partial and transient protection against subsequent infection by other serotypes2. According to WHO, 50 million dengue infections occur worldwide with endemic disease seen in more than 100 countries in Africa, America, Eastern Mediterranean, South East Asia and Western Pacific3.

During dengue outbreak the rate of infection in general population goes from baseline of 40% to 50% to 80% to 90%, an estimated 500,000 people with DHF require hospitalization each year which include mostly children than adults, and about 2.5% will die4. The case fatality rate can be reduced up to 1% if access to medical care is improved along with awareness and knowledge regarding dengue fever5. The spread of dengue is attributed to expanding geographic distribution, rapid rise in urban population, increased human-vector contact, water storage in the households and inadequate solid waste disposal services2.

In Pakistan first confirmed epidemic of dengue fever occurred in Balochistan in 1994 among workers of a power generation plant. Majority were positive for IgM antibodies and multiple dengue sero types were detected6. Second epidemic occurred in 2011 after rainy season, all over Pakistan but people of Punjab were mostly affected7. From 2011, onwards cases of dengue infections are being reported regularly and throughout the year with highest rates in post rainy seasons.

Patients, Methods and Results

This report presents the retrospective analysis of three years (2011-13) surveillance data of dengue fever in Karachi. The data was sent to Dengue Surveillance Cell from thirty (30) hospitals of Karachi including three major public and four major private sector hospitals of patients who visited indoor and outdoor facilities during 2011-13. SPSS version 15 was used for descriptive analysis.

Over 3 years study period, 7783 dengue cases were reported at the dengue surveillance cell Karachi. There were 5016 (64%) males with male to female ratio of 1.8:1. Age distribution showed that 3482 (45%) individuals were in the age group of 19-35 years and only 306 (4%) were over 60 years of age. Majority i.e. 6772 (87%) were residents of Karachi. Almost 54% required hospitalization while 3598 (46%) were treated in out patient departments (Table).

Table: Dengue infection in different age groups.

Age groups###2011###2012###2013###Total


less than 5 years###71(6)###26(4)###282(5)###79(5)

6-12 years###117(11)###71(10)###545(9)###733(9)

13-18 years###120(11)###110(15)###940(16)###1170(15)

19-35 years###461(43)###287(39)###2734(46)###3482(45)

36-60 years###257(24)###192(26)###1264(21)###1713(22)

reater than 60 years###53(5)###48(6)###205(3)###306(4)


Maximum cases of dengue infection were seen in October (32%, n = 2478) followed by September and November (21%), while it was least (0.4%) were seen in January and February.

Out of 7783 reported cases from different hospitals, ELISA was used for the diagnosis in 6704 cases where as in the remaining 1079 cases the type of diagnostic test done was not mentioned. Out of 6704 cases tested on ELISA for dengue infection, 1295 (19%) cases were negative for both IgM and IgG while 5409 (81%) were IgM or IgG positive. Within these 5409 cases, 3930 (73%) were IgM positive (primary infection) while 1479 (27%) were both IgM and IgG positive (secondary infection). About 6156 (92%) individuals presented with high grade fever, 106 (2%) with hemorrhage and 200 (3%) had platelet count of less than 50,000/ cmm. Overall case fatality rate was 1%.


The present review shows highest dengue infection in adult males in post rainy season. The consequences of dengue fever is loss of workdays for people dependent on wage labor whereas, consequences of severe illness like hemorrhagic fever and shock syndrome need hospitalization and specific treatments with high mortality making its management beyond the reach of poor people. In developing countries like Pakistan demographic, economic, behavioural and social factors are important determinants for the control of dengue infection and for successful public health interventions.

Previously dengue was considered a childhood disease however after 1980 there is increasing incidence of dengue among adults8,9. Similar finding was noted in this study where a shift age was noted with majority of cases falling between 19-35 years. This finding is consistent with other studies in Asia including Singapore, Indonesia and Bangladesh where workers also reported high incidence of dengue infection in adult age group between 15-34 years10-12.

The present study showed a male preponderance with male to female ratio of 1.8:1. This is similar to the findings of few hospital based studies conducted in India (1.9:1) and Singapore (1: 0.57)13,14. The male exposure need to be looked into cautiously as in our society women are less likely to be taken to a hospital unless very ill.

Literature showed that dengue outbreaks occur in rural settings in Asia but in our situation it has affected urban population which may be due to increased population movement15. Rate of infection was highest in post rainy season conferring to El Nino phenomenon but data from Puerto Rico revealed herd immunity, introduction of new serotype and change in demographic factors as an important cause of dengue outbreak16. Social and economic factors play a vital role in the incidence and prevalence of dengue infection, e.g. air conditioning, screens and safe water supply in developed countries help in the prevention of disease and improved health services reduce mortality whereas in our setting unplanned urbanization, unsafe water supply, uncovered water utensils, collection of rainy water, open ditches, flowing sewers are considered as important factors for an outbreak17.

Data needs to be collected and compared on long term basis to see the trends. Geographical mapping may be done to identify the high incidence areas and plan interventions accordingly.


Programme Manager offers to thank all heads of the hospitals who provided data for the surveillance cell.


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12. Rahman M, Rahman K, Siddique AK, Shoma S, Kamal AH, Ali KS, et al. First outbreak of dengue hemorrhagic fever, Bangladesh. Emerg Infect Dis 2002; 8: 738-40

13. Agarwal R, Kapoor S, Nagar R, Misra A, Tendon R, Mathur A, et al. A clinical study of the patients with dengue hemorrhagic fever during epidemic of 1996 at Lucknow, India. Southeast Asian J Trop Med Public Health.1999; 30: 735-40

14. Goh KT, NG SK, Chan YC, Lim SJ, Chua EC. Epidemiological aspects of an outbreak of dengue fever/dengue hemorrhagic fever in Singapore. Southeast Asian J Trop Med Public Health 1987; 18: 295-302.

15. Muto RSA. Dengue fever/dengue hemorrhagic fever and its control-status. In: WHO. Internal report Western Pacific Region. Manila: WHO;1999; p.4.

16. Hay SI, Cox J, Rogers DJ, Randolph SE, Stern DI, Shanks GD, et al. Climate change and the resurgence of malaria in East Africans highlands. Nature 2002; 415: 905-9

17. Reiter P, Lathrop S, Bunning M, Biggerstaff B, Singer D, Tiwari T, et al. Texas lifestyle limits transmission of dengue virus. J Emerg Infect Dis 2003; 9: 86-9.
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Publication:Pakistan Journal of Medical Research
Article Type:Report
Date:Sep 30, 2015
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