Investigation of Dengue Fever Outbreak in a Rural Area of Islamabad, Pakistan: A Case Control Study

Background: In the second week of October 2019, five suspected cases of dengue fever were reported from union council Sohan, Islamabad rural (population 45,747) to the health department, Islamabad Capital Territory (ICT).  Outbreak investigation was conducted with the objectives to identify risk factors and to recommend control measures. Methods: Outbreak investigation was conducted from 17 th October to 25 th November 2019. A case was defined as, “fever and two or more of the following signs/symptoms; headache, retro-orbital pain, joint/bone pain, myalgia and petechial rash with NS1 test (Nonstructural Protein 1) positive during 8 th October to 25 th November 2019 among residents of Sohan”. Age and sex-matched controls were recruited from the same neighborhood. All cases were positive for NS1 antigen. Blood samples from five suspected cases were collected and tested for laboratory confirmation. Results: A total of 547 households were surveyed and 85 cases were identified. The mean age was 34.4 years + 16.05 (range 3-71 years). The attack rate was 0.19% whereas the most affected age group was the 45-54 years (AR 0.43%). Males were predominantly affected (n=48 56.5%). Among all cases, 32% (n=27)) had stagnant water inside or around their houses (aOR 2.65, CI 1.20-5.83, P= 0.005), 33% (n=28) were using mosquito repellent (aOR 0.35, CI 0.17-0.70, P <0.001), 31% (n=26) used indoor residual spray insecticide (aOR 0.48, CI 0.24-0.97, P =0.041), and 73% (n=62) used full protective clothing (aOR 0.17, CI 0.05-0.58, P <0.001). All five blood samples were tested positive for NS-1 antigen. Conclusion: The presence of accumulated rainwater in pools and empty receptacles around houses acted as breeding grounds for Aedes aegypti mosquitos and was the most probable cause of this outbreak. Following our recommendations, the health department-initiated mosquito breeding sites control activities through residual insecticide spray and advocacy on the use of protective measures against mosquito bites.