Demographic and clinical features of dengue fever in Pakistan from 2003-2007: a retrospective cross-sectional study

Abstract

Background: Demographic features of dengue fever have changed tremendously in Pakistan over the past two decades. Small scale studies from all over the country have reported different aspects of individual outbreaks during this time. However, there is scarcity of data looking at the overall trend of dengue virus infection in the country. In this study, we examined annual trends, seasonality, and clinical features of dengue fever in the Pakistani population.

Methods: Demographic information and dengue IgM status of all patients tested for dengue IgM antibody at Aga Khan University Hospital from January 2003 to December 2007 were analyzed to look for trends of IgM-positive cases in Pakistan. In addition, clinical and biochemical parameters were abstracted retrospectively from medical records of all patients hospitalized with IgM-proven dengue fever between January 2006 and December 2007. These patients were categorized into dengue fever and dengue hemorrhagic fever according to the WHO severity grading scale.

Results: Out of a total of 15,040 patients (63.2% male and 36.8% female), 3952 (26.3%) tested positive for dengue IgM antibody. 209 IgM proven dengue patients were hospitalized during the study period. During 2003, IgM positive cases were seen only during the months of July-December. In contrast, such cases were detected throughout the year from the 2004-2007. The median age of IgM positive patients decreased every year from 32.0 years in 2003 to 24.0 years in 2007 (p<0.001). Among hospitalized patients, nausea was the most common presenting feature found in 124/209 (59.3%) patients. Children presented with a higher median body temperature than adults (p = 0.010). In addition, neutropenia was seen more commonly in children while raised serum ALT levels were seen more commonly in adults (both p = 0.006). While a low total white cell count was more common in patients with dengue fever as compared to Dengue Hemorrhagic Fever (p = 0.020), neutropenia (p = 0.019), monocytosis (p = 0.001) and raised serum ALT level (p = 0.005) were observed more commonly in the latter group.

Conclusions: Dengue virus is now endemic in Pakistan, circulating throughout the year with a peak incidence in the post monsoon period. Median age of dengue patients has decreased and younger patients may be more susceptible. Total and differential leukocyte counts may help identify patients at risk of hemorrhage.

Figure 1. Geographical distribution of cities with laboratory collection points in Pakistan.

This map presents the geographical distribution of cities with laboratory collection points from where samples used in this study were received. Colours denote the four provinces of Pakistan as described in the legend. Aga Khan University Hospital (AKU, Karachi) was the study center.

Figure 2. Quarterly distribution of the percentage of Dengue IgM positive cases by year.

In 2003, Dengue IgM positive cases were only observed to appear in the months of July- December. This trend changed from 2004–2007, when IgM positive cases were detected throughout the year. Dengue IgM positive cases were most prevalent in the fourth quarter (October–December) from the years 2003 to 2006.

Figure 3. Median age of patients from 2003–2007.

The median age of patients has decreased between the years 2003 and 2007.

Figure 4. Comparison of total and differential leukocyte counts between dengue fever(DF) and dengue hemorrhagic fever(DHF).

Patients with DF were more likely to have leukopenia (p = 0.015) with a normal differential count while patients with DHF were more likely have a normal TLC count, with neutropenia (p = 0.018) and monocytosis (p = 0.001).