Research Article

Using a Cluster Survey to Reconstruct and Estimate the Magnitude of a Major Dengue Outbreak in El-Obeid, Sudan

by Hassan E El Bushra1*, Adam Musa Adam Eissa2, Mahmoud Hassan Hilali3, Iman Malik Abdel Rahman4, Youssif AR Ahmed Mustafa5, Abuelez Hassan Ibrahem Abdallah6, Mohamed Ahmed Agab7, Eiman Karrar8, Mohamed Abdalhafiz Alkhidir9

1Independent Consultant Medical Epidemiologist, World Health Organization (WHO), Country Office, Khartoum, Sudan

2Associate Professor of Public Health. Faculty of Medicine and Health Sciences, University of Kordofan, El-Obeid, Sudan

3Head, Epidemiology Department, Blue Nile National Institute for Communicable Diseases, Bihos street, Wad Medani, Gezira, Sudan

4Director General, Health Affairs, State of North Kordofan, and Assistant Professor of Community Medicine, Faculty of Medicine and Health Sciences - University of Kordofan, El-Obeid, Sudan

5Virology Department, National Public Health Laboratory, Federal Ministry of Health. Khartoum, Sudan

6Assistant Professor of Community Medicine, Faculty of Medicine and Health Sciences, University of Kordofan, El-Obeid, Sudan

7Assistant Professor of Medicine, Faculty of Medicine and Health Sciences, University of Kordofan, El-Obeid, Sudan 8UNICEF Country Office, Khartoum, Sudan

9World Health Organization, Country Office, Khartoum, Sudan

*Corresponding author: Hassan E. El Bushra, Consultant Medical Epidemiologist, World Health Organization, Othman Digna Street, Corner Nile Avenue, Eastern Gate, Khartoum, P.O Box 2234, Khartoum, Sudan

Received Date: 06 May, 2024

Accepted Date: 14 May, 2024

Published Date: 17 May, 2024

Citation: El Bushra HE, Adam Eissa AM, Hilali MH, Abdel Rahman IM, Ahmed Mustafa YAR, et al. (2024) Using a Cluster Survey to Reconstruct and Estimate the Magnitude of a Major Dengue Outbreak in El-Obeid, Sudan. J Community Med Public Health 8: 437.


Introduction: Dengue fever surveillance in El-Obeid, Sudan, identified approximately 572 cases. To estimate the outbreak’s true magnitude, a community-wide cluster survey was conducted. Methodology: Eighty clusters, each comprising ten households, were chosen via systematic random sampling. Rapid diagnostic tests were used on blood samples from symptomatic and asymptomatic individuals within each household. Results: There were discrepancies between the official surveillance system and the cluster survey. The cluster survey revealed a delayed detection, a wider spread of the virus, and a significantly higher number of cases compared to the official data. The cluster survey of 1285 participants residing in approximately 4,800 households identified a high prevalence of dengue markers (35.3%). This translates to an estimated 323,604 individuals (extrapolated from total population) with potential past or present infection. About 24.7% of the sample were positive for IgM, 25.1% for IgG, and 1.7% for NS-1, indicating an estimated 14,930 individuals with potentially infectious cases. Investigations in El-Obeid City health facilities revealed critical shortcomings in the dengue outbreak response. These included severely limited communication between preventive and curative healthcare, a barely functional public health laboratory hindering diagnostics, and a shortage of trained staff, highlighting broader resource constraints. Additionally, inadequate public awareness campaigns failed to effectively reach the population. Conclusions: Combining data from both surveillance and the cluster survey provided valuable insights into the El-Obeid dengue outbreak. The survey revealed a delay in detection and underreporting by the existing system. It also likely increased awareness among healthcare workers and the public, potentially improving case detection and control measures. This integrated approach highlights the importance of using multiple data sources for a more comprehensive understanding of outbreaks.

Keywords: Dengue; Sudan; Cluster survey; Outbreak; Attack rate; Sentinel surveillance


Dengue Fever (DF), a mosquito-borne viral illness, poses a significant public health threat, particularly in tropical and subtropical regions, including Sudan. DF is a self-limited illness currently lacking a specific antiviral treatment; secondary infections with different dengue virus serotypes can lead to the potentially fatal complications [1-3]. Sudan has a documented history of recurring dengue outbreaks, with episodes concentrated in eastern and western regions bordering countries with established dengue transmission [4-9].

In 2019, several Sudanese states experienced outbreaks of DF, culminating in El-Obeid City, North Kordofan. Despite the clear presence of an overwhelming outbreak in El-Obeid, the precise magnitude and geographic distribution remain unclear, with the potential for underestimation. This study employs a cluster survey approach to reconstruct the outbreak’s timeline and estimate its true size. Our primary objectives are to definitively confirm the occurrence of the outbreak within El-Obeid City limits, assess its overall magnitude, and to assess the sensitivity, reliability, and timeliness of the sentinel surveillance system in detecting and monitoring the dengue outbreak within El-Obeid city.

Material and Methods

Study Setting

El-Obeid City, (Figure 1) the capital of North Kordofan State in Sudan, has an estimated population of 936,359 inhabitants. This semi-arid city experiences distinct wet and dry seasons. El-Obeid City serves as a critical transportation hub and regional commercial center for western Sudan. Yet, El-Obeid has unfortunately faced a longstanding challenge: a critical water shortage [10]. This scarcity compels residents to store water in various containers, a practice that inadvertently creates ideal breeding grounds for Aedes mosquitos, the primary vectors of dengue fever transmission.

Figure 1: Map of El-Obeid, Capital City of North Kordofan. Map for North Kordofan state: bordering Northern, River Nile, White Nile, South Kordofan, West Kordofan, and North Darfur states

Study Design and Sampling

This study utilized a descriptive survey that collected data to gain a comprehensive understanding of the dengue fever outbreak’s scale and spread within El-Obeid City. To ensure a representative sample across the entire city, a systematic random sampling technique was employed. El-Obeid City map was divided into a 27x27 grid system, resulting in a total of 729 individual pixels. From this grid, 80 sampling “pixel units” were chosen using systematic random sampling. Each pixel represented a square area measuring 400 meters wide (Figure 2). This specific size and number of pixels balanced capturing a representative sample with maintaining a manageable workload for the survey teams. Within each selected pixel (grid square), the first house was chosen randomly. To ensure ten households were included from each pixel, subsequent households were selected by identifying the nearest house to the previously chosen one.