Principal Findings
This study showed that males were more affected than females, and the young age group of 21 to 30 years was the most severely affected (AR=40%). Stored water in containers inside houses and subsequent mosquito breeding were the most probable causes of the outbreak and the use of mosquito repellents had a protective effect. Dengue affects all age groups including infants and adults [17]; however, children usually tolerate this infection better than adults [18]. Our results support this finding, as there were only 3 children under 10 years of age admitted during this outbreak and none in infancy.
Simmons et al found that in mild dengue cases, laboratory analysis shows no significant changes except for abnormal leukocyte counts and moderate elevation of the hepatic amino-transferase enzyme activity [19]. This phenomenon was observed in our study too, where there was no significant difference between the laboratory parameters of the cases and controls.
In our study, the case fatality rate was 0.53%, showing that timely medical care and symptomatic management saved lives. Gubler states that the case fatality can be reduced to less than 1% with correct and timely treatment [20]. Akhter emphasizes that even patients with complications can be cured if given supportive and adequate treatment [21]. This explains the low case fatality during this outbreak, as the government had referral hospitals (Holy Family Hospital, Rawalpindi) and had devised the diagnosis and management criteria for all suspected, confirmed, and complicated DF cases at primary and secondary care hospitals.
According to the classification schemes of the World Health Organization, leukopenia in patients with febrile illness is one of the key findings when suspecting dengue infection [22]. In the present study, most of the patients presented low leukocyte levels and relatively better hemoglobin levels. The average leukocyte count was 4.5 among the admitted dengue patients. Other studies have documented that case fatality rates of dengue increase when infection occurs in patients with other acute or chronic diseases like asthma, diabetes, and hypertension [23,24].
Vector control is crucial in preventing DF. Along with the availability of impregnated bed nets, other measures like window curtains and water container covers treated with long-lasting insecticide have been tested in dengue endemic countries [25]. Only 48 individuals out of 373 were using mosquito repellents or any kind of protection against mosquitos; however, in the control group, 199 used mosquito repellents and this proved protective.
There are 4 distinct dengue virus serotypes that cause dengue (DEN-1, DEN-2, DEN-3, and DEN-4) [1]. During this outbreak, 322 blood samples were tested. DEN-2 (n=126, 39%) was the most prevalent serotype, followed by DEN-3 (n=96, 30%), DEN-4 (n=58, 18%), and DEN-1 (n=42, 13%). In previous outbreaks of dengue reported from different cities of Pakistan, DEN-2 remained the prominent serotype. In the dengue outbreaks in 2008 and 2009, DEN-2, 3, and 4, and DEN-2 and 3 were prominent, respectively [26]. Similarly, according to dengue case data from Sheikhupura and Gujranwala districts, DEN-2 was the most prevalent, followed by the DEN-1 serotype 1 [27].
Most of the cases were males with a male-to-female ratio of 3:1. This finding confirms those of previous studies [28,29]. Male predominance may be due to multiple reasons. Males are usually responsible for taking children early in the morning to school, and they go out for work. They are also responsible for bringing food and other items in the evening. As it was summer, males usually wore thin clothes with half sleeves, thus becoming more vulnerable to mosquito bites. In comparison, females stay at home and according to the local culture, they are well covered. Fatima reported the same findings where 73% of the cases comprised males and the mean age of the subjects was 34 years with a range of 5 to 80 years [30]. Similar results were obtained in our investigation where the mean age was 36 years (range 10-69 years).
The presence of stored water in homes, usually in open containers, for domestic use was observed because of intermittent water supply. Storing water was found to be a risk factor for spreading DF. Out of the 373 dengue cases, 307 had intermittent water supply and 219 were storing water at home for domestic and drinking purposes (OR 2.04, P<.001), and 196 had stagnant water pools, ponds, or passages near their homes. Fatima reported that the source of water supply is a risk factor for DF [30]. This finding supports the findings of another study from Vietnam [31]. This study also states that the absence of taps was strongly associated with DF. Apart from stored water in homes, open wells were the major source of water supply for the study population and both factors promoted vector breeding. Phoung et al highlight the same issue, identifying that mosquito larvae in water containers and gardens near houses are the most important risk factors for dengue transmission [32].
Recently, Wang et al have described that there are several risk factors that correlate with dengue hemorrhagic fever, including viral, epidemiological, human, and abiotic factors [33]. Another study conducted among young children has revealed the same risk factors as those identified in our study. Among the people in the study population, those storing water in their homes and consistently covered the storage containers did not develop dengue as opposed to those who did not. Similarly, the positivity of the dengue virus was significant (P<.001) among children who did not regularly wear long-sleeved shirts and full pants [34].
Consequently, different prevention and control activities were performed during the outbreak, including awareness campaigns about DF, filling of stagnant water reservoirs, and discouraging water storage at home. Insecticide-treated bed nets were distributed, and their use was demonstrated.