With an estimated 50 million infections per year across many countries, Dengue is now recognized as one of the major public health problems worldwide [1] . It is a mosquito-borne illness belonging to the genus flavivirus and consisting of 4 distinct serotypes, namely DENV-1, DENV-2, DENV-3 and DENV-4 [2] . In majority of the cases, the illness is self-limiting with mild symptoms such as fever, rash and joint pain (Dengue Fever). However, this may predispose to a severe form (dengue hemorrhagic fever) with infection with a different serotype [3] [4] .

Today, dengue is endemic in more than 100 countries across Asia, Africa, America, Eastern Mediterranean, and West Pacific. Central to this is the enlarging habitat of its vectors, Aedes aegypti and Aedes albopictus. Aedes aegypti in particular, is highly adaptive in crowded areas; hence epidemics have been seen in cities with un-planned urbanization and overcrowding [5] [6] .

Pakistan also had its share of dengue outbreaks in the recent years owing to the factors mentioned above. Epidemics have been reported especially in urban areas of Karachi and Lahore; situation worsening especially after monsoonal rains and floods. In October 2010, a total of 1809 cases were suspected out which 881 cases were confirmed of Dengue infection [7] . In 2011, worst outbreak occurred in the country when more than 14,000 people were affected with dengue with over 300 deaths [8] .

Considering the current situation of Dengue virus and unavailability of data in Pakistan urgent attention and oversight is required to ensure effective preventive and curative program development. The objective of this study was to estimate the proportion of Dengue virus specific IgG ELISA among asymptomatic children between the ages of 1 year to 15 years, residing in an urban population of Karachi. When re-infected this population would potentially be at a higher risk of developing severe forms of dengue hemorrhagic fever.

Table 1 shows the different characteristics of the population by IgG positivity. A total of 900 subjects, comprising of 461 males and 439 females, were surveyed, from which 419 (46%) had IgG antibodies in their blood. The mean age for IgG positive subjects was relatively higher to the IgG negative subjects (9.5 ± 3.7 years vs. 6.7 ± 4.2 years; p-value < 0.001). About 61% children, with positive IgG were of the age of more than 10 years (Figure 1).

Household characteristics revealed that likelihood for previous dengue infection is more when hand washing is not practiced and no water purifying measures are taken. Likelihood for previous dengue infection is more if the average monthly income is less than Rupees 8000 (Table 1).

¹Expressed as n (%).

Table 2 summarizes the adjusted logistic regression model signifying preponderance patterns for IgG positive subjects. Male children of increasing age were more likely to be IgG positive. The data also shows that children with anemia or thrombocytopenia were less likely to have had a previous dengue infection. The adjusted model revealed that households with lower average income and no water purifying method employed resulted in greater preponderance of previous dengue infection among the target population.

Our study indicated that 46% of the population had been infected with dengue virus, making them susceptible to severe forms of dengue fever. To date, no study of this sort had been conducted from Karachi, Pakistan.

Our study showed that Dengue IgG was found more in elderly children (more than 5 years). This finding has also been reported by other researchers in their settings [9] - [11] . Our study also showed greater preponderance of dengue IgG antibodies in males compared to females. Where reports suggest no significant differences associated with sex that might be different from Pakistan’s perspective owing to the fact that majority of the females remain indoors while males spend their maximum time outside [11] - [13] . As mentioned previously, the dengue vectors are highly adaptable to any environment, hence it is probable for male children of such ages to become exposed to its habitat more often and contracting the virus.

In our study, analysis revealed dengue IgG positivity to be more among lowest categories of socioeconomic position, comprising of 19% of the studied population. This was consistent with the study reported from Brazil [13] [14] . In our study, the finding was perhaps expected as Garden is a modern urban area with high rise buildings and inhabited by affluent communities.

Employing strategies for water purification was also found to be important in the study, indicating a more likelihood to prior dengue infection in absence of water purification. In our analyses, 39% reported to purify water for consumption, using methods such boiling (15%), filtering (0.02%) and chlorination (0.001%). It can be conceived that untreated water would be the possible niche for the Aedes mosquitoes to breed and multiply.

Unique in this study is the positive association of stunting with IgG positivity (Χ² = 4.12, df = 1, p-value = 0.042). Our analysis also revealed a lesser likelihood of IgG positivity in presence of anemia and thrombocytopenia. These 3 conditions are pretty prevalent in this part of the world, each clinical correlate limiting us to offer any interpretation to its significance with IgG positivity.

Some limitations are to note in this study. For instance we opted to collect information from a relatively affluent community of Karachi. Though previous studies on Dengue from around the world have indicated Dengue to be a threat for the urban areas, including squatter settlements would have provided a comparative picture showing proportional associations of positive IgG with overcrowding, sanitation and presence of domestic animals [6] [7] . The important and interesting aspect is to assess the serotype of the most prevalent dengue virus in these settings, as limited literature suggests DENV-2 and DENV-3 to be most prevailing in Pakistan [7] .

The study indicates a significant part of the population of children less than 15 years in Garden, Karachi is infected with Dengue virus. Though severe dengue infections occur in a comparatively smaller population, but the children identified in this study are definitely at risk of severe complications in case of re-infection [6] . New cases are reported with the advent of monsoons and monsoonal rains. Pakistan has received its share of monsoon rains and potentially at risk for another dengue outbreak. Despite public and private measures for containing the infection, we are far away from reducing the rates of dengue in our population. Serious measures are needed to control the mosquito vector populations and reduce the associated morbidity and mortality, as seen in the previous years.

The study was carried out using the Aga Khan University Seed Money Grant awarded to SA.

The authors declare no competing interests.

SA, SRA and FT were involved in data collection, entry, analysis, revision and manuscript writing.

SA was involved in study conception, manuscript writing, data collection, entry, analysis editing and overall supervision.

All authors have read and approved the final manuscript.

There is no additional data available.