Dire Dawa administration city is found 515 Kilometers south east of Addis Ababa, the capital of Ethiopia. The council has a total approximate population of 400,000 and nine operational districts (4 rural and 5 urban districts). It is further classified into 10 urban and 37 rural kebeles, the smallest administrative unit in Ethiopia. About 70% of the people live in the city while the rest are in the surrounding rural kebeles. Moreover, the council has 2 government owned Hospitals, 15 health centers and 31 health posts. Additionally, there are 3 private hospitals and 21 private clinics. There are both arid and semiarid climatic zones in the council. The north eastern part of the city is relatively sparsely populated lowland exhibiting agro-pastoral and pastoral system, and the southeastern part uses mixed farming system. The city lies between 1000 to 2000 m above sea level with an average monthly temperature of 24.8 oC and annual rainfall of 604 mm [10, 11]. The warm climate of the City is favorable for the transmission of vector borne diseases like malaria and DF.
An unmatched case-control study design was used to investigate the outbreak. All residents of Diredawa Administration city were the source population. Cases were either confirmed or epidemiologically linked Dengue Fever cases while Controls were all people without Suspected DF symptoms. Additionally, confirmed cases were suspected cases with laboratory confirmation (positive IgM antibody, rise in IgG antibody titers, positive PCR or viral isolation). Moreover, epidemiologically linked cases were suspected cases presented at the location of ongoing outbreak within previous two weeks of onset of an acute febrile illness or dengue, or association in time and place (e.g., household member, family member, classmate, or neighbor) with a confirmed or probable dengue case.
All confirmed or epidemiologically linked cases of Dengue fever found in Health facilities from October 7 to 15, 2015 were included in the study. For the Controls, resident of Diredawa Town who was a neighbor to a case and who did not develop signs and symptoms of DF were included. On the other hand, Suspected Dengue fever patients who were critically ill and controls who were not a permanent resident of Diredawa city were excluded from the study. This study was carried out from October 7 to 15, 2015 at various private and public hospitals including health centers and private clinics of Diredawa. Health facilities were selected based on case load and all confirmed and epidemiologically linked cases at the health facilities during the investigation period were enrolled. Approval of the health facilities administration was obtained before approaching the patients. A total of 70 cases were interviewed with a ratio of 1:2 making the controls 140. Controls were neighbors of cases. After each case was interviewed at the hospital, their houses were visited and neighbors were interviewed.
The data was collected through face to face interview using structured questionnaire initially prepared in English and then translated to Amharic (Additional file 1). The questionnaire was divided in to three main areas covering demographic variables, risk factors associated with Dengue fever and Knowledge regarding the disease. For verifying consistency, a pre-tested questionnaire was used.
Sixty-nine serum samples were collected from malaria negative suspected patients by skilled professional and sent to Ethiopian Public Health Institute (EPHI) national laboratory. Samples were collected to identify the cause of the outbreak. The outbreak was confirmed first by RDT and then RT-PCR was performed for confirmation.
The data was checked for completeness and consistency and analyzed using SPSS version 20 software. Associations between factors and Dengue Fever status were tested first by the chi-square test and for cells with values less than 5, Fisher’s exact test was applied. In order to investigate relative importance of the variables in relation to the dependent factor and any confounding between them, they were fitted in a binary logistic regression model to identify independent factors. Those variables that come significant in the bivariate analysis were fitted to a multivariable analysis followed by a backward stepwise procedure to control confounding. Results were displayed using texts, tables and graphs and statistical significance was interpreted using Odd ratio with 95% confidence interval and P value < 0.05.
Ethical clearance was obtained from EPHI. A letter was written for the regional health bureau in order to obtain approval on the data collection. An informed consent was obtained from all study participants. Where the age was less than 16 years, assent was obtained from the children/adolescents and permission was obtained from respective parents/guardians. Confidentiality of information was assured and ensured. Participants were treated with respect and willingly participated in the study with no payment or coercion.