Risk factors associated with Dengue fever outbreak in Islamabad, Pakistan (Preprint)

BACKGROUND On 23rd Oct 2016, 79 dengue fever cases were reported from the Union Council (UC) Tarlai to Federal Disease Surveillance and Response Unit Islamabad. A team was deputed to investigate the suspected dengue outbreak. OBJECTIVE This study was aimed to determine the extent of the outbreak and identify the possible risk factors. METHODS Active case finding was conducted through a house-to-house survey. A case was defined as, acute onset of Fever ≥ 38 ℃ in a resident of Tarlai from Oct 2-Nov 11, 2016, with a positive NS-1 test, and any two of the following signs and symptoms; retro-orbital/ocular pain, headache, rash, myalgia, arthralgia, and hemorrhagic manifestations. A structured questionnaire was used to collect data. Age and sex-matched controls (1:1) were identified from the same area. Blood samples were taken and sent to the National Institute of Health for genotype identification. RESULTS During the active case search, 145 cases of dengue fever were identified by surveying 928 houses from 23rd Oct to 11th Nov 2016. Attack rate (AR) was 17.0/10,000 population. The mean age was 34.4±14.4 years. More than half of the cases were male (n=80, 55.2%). Among all cases, 29% belong to the 25-34 years age group while the highest attack rate was found in 35-44 years (AR 35.6/10,000) followed by 55-64 years (AR 35.5/10,000). All five blood samples tested positive for NS-1 (genotype DENV-2). The most frequent presenting sin/symptom was fever and headache (100%). Stagnant water around houses (OR = 4.86, CI: 2.94 -8.01, P<0.0001), presence of flower pots in-home (OR = 2.73, CI: 1.67-4.45, P<0.0001), and open water container (OR 2.24, CI: 1.36-3.60, P<0.0001) showed higher odds among cases. While. use of bed nets (OR 0.44, CI: 0.25-0.77, P 0.003), insecticidal spray (OR 0.33, CI: 0.22-0.55, P<0.0001), door screening (OR 0.27, CI: 0.15-0.46, P<0.0001), use of mosquito coil/mat (OR 0.26, CI: 0.16-0.44, P<0.0001) and cleanliness in house (OR 0.12, CI: 0.05-0.26, P<0.0001) showed a significant protective effect. CONCLUSIONS Stagnant water acting as breeding grounds for vector was the probable cause of the spread of the outbreak. The establishment of a surveillance and early reporting system and the use of protective measures against the vector is strongly recommended.