Epidemiological investigation of a Dengue fever outbreak in Hodan District, Banadir region, Somalia

Saido Gedi^1,&, Ahmed Mohamed Fidhow², Kasim Sultan Mahdi³

 

¹SOM-FETP program, Public Health Emergency Operations Centre (PHEOC), Mogadishu, Somalia, ²World Health Organization (WHO), Garissa, Kenya, ³African Field Epidemiology Network (AFENET), Mogadishu, Somalia

 

 

^&Corresponding author
Saido Gedi, SOM-FETP program, PHEOC, Mogadishu, Somalia

 

 

 

 

Dengue fever (DF) is a mosquito-borne infectious disease caused by the dengue virus, belonging to the genus Flavivirus, the family Flaviviridae [1]. DF is common in warm, tropical climate and that causes a flu-like illness. Disease transmission to humans is through the bite of an infected female Aedes aegypti mosquito, which is a day-time feeder; its peak biting periods are early in the morning and in the evening before dusk. The Aedes aegypti mosquito lives close to human populations, laying its eggs in water-filled containers inside the house or surrounding areas, including non-used bottles, containers, discarded waste and tyres which hold water [2].These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses. There are four closely related dengue virus serotypes, DENV1, DENV2, DENV3, and DENV4. Additionally, infection can be transmitted through blood transfusion or organ transplantation or transmitted vertically from mother to child. The mosquito becomes infected when it bites a person whose blood contains the dengue virus. Symptoms usually begin three to fourteen days after infection and they may include high fever, headache, vomiting, muscle and joint pains, and a maculo-papular rash [2]. Although less common, some people develop severe dengue, such as severe bleeding, and organ impairment. There is no effective antiviral treatment for dengue, but recovery usually takes two to seven days [2]. The best way to protect against the dengue virus is to avoid mosquito bites.

 

The incidence of dengue has grown dramatically around the world in recent decades. Over 50% of the world´s population residing in tropical and subtropical countries is at risk [2]. Approximately 3.6 billion people are currently at risk of dengue infection in more than 100 countries in Asia, America, and Africa [3]. Dengue fever infections in Africa remain largely unknown but recent outbreaks suggest that key areas of the continent may be at increased risk of dengue transmission and an estimated 390 million dengue infections occur worldwide annually. Before year 2000, DENV2 was the most reported serotype in Africa, which was the cause of multiple epidemics in Somalia, Djibouti, Kenya, and Tanzania as well as a sylvatic emergence with sporadic human cases in Senegal and Burkina Faso [4]. Only Mozambique (1985) and Somalia (1993) saw the emergence of DENV3. Somalia reported dengue outbreak in 2011 among African Union Mission in Somalia (AMISOM) peacekeepers in Mogadishu [5]. A majority (82%) were positive for dengue virus (DENV). The second outbreak of dengue fever was reported in 2013, where 60 cases were detected in the country. Dengue fever remains high in Somalia, because of the practice of storing water in open containers which provides breeding grounds for the vector that transmits the disease.

 

On 18 October 2022, the Office of Emergency Department of Federal Ministry of Health was notified of a death case of dengue and two confirmed cases in Banadir region, Mogadishu, Somalia. The first case of dengue fever was confirmed in Ladnaan Hospital, Hodan district, Banadir Region on 11 September 2022.The Ministry of Health (FMoH) together with National Institute of Health (NIH) convened a meeting to coordinate an outbreak investigation team and Dengue Fever Preparedness Rapid Response Team was established. An investigation was launched between 20 November 2022 - 14 December 2022, to confirm the existence of the dengue outbreak, to describe the dengue cases by time, place and personal characteristics and recommend appropriate prevention and control measures.

 

 

The investigation period and area

 

We investigated suspected dengue fever outbreak from 20 November to 14 December 2022. The study was conducted in Hodan district, (Figure 1) which is located at the heart of the Banadir region in the capital city-Mogadishu. Hodan District is one of the 17 districts in the southeastern Banadir region of Somalia. The district comprises of four sub sections: Taleex, Ka´aan, Oktobar and Ahmed Gurey. The total population of the Hodan district is 164,941 (PESS 2021). The district has a total of 51 Health facilities out of which three are public health facilities, and 48 are private hospitals. There is no suitable waste disposal area or sewage system in the area.

 

Study design

 

A cross-sectional study was conducted in Hodan district from 11 September to 14 December 2022 involving both a review of medical records and visits to the households of confirmed cases. Descriptive epidemiological analysis was used to describe the outbreak using person, place, and time variables.

 

Case definition We used WHO standard case definition of Dengue Fever to enroll the cases as following.

 

Dengue Fever: is defined as any resident person in Hodan district that has developed a sudden fever of more than 38°C for 2 to 10 days with at least two of the following signs and symptoms: myalgia, maculo-papular rash, hemorrhagic manifestations, or leukopenia from September—December ,2022.

 

Confirmed Dengue Fever: any resident of Hodan district who was a suspected case (Fever, myalgia, rash, hemorrhagic manifestations, or leukopenia) and with positive IgM DENV laboratory confirmation.

 

Data collection procedure

 

We collected data by reviewing existing medical records, and created a line list with cases that were suspected and epidemiologically linked cases at the health facilities as probable cases. Data were obtained from the laboratory in an Excel sheet. The data regarding demographic characteristics (gender, age, and subsection), were collected using on a standardized tool from the Arboviral diseases line list (https://www.who.int/emergencies/outbreak-toolkit/standardized-data-collection-tools). The suspected cases´ blood samples were collected. The collected blood sample specimens were transported to National Public Health Reference Laboratory for confirmation. In addition, we also explored potential risk factors by visiting and engaging face-to-face interview with the confirmed cases.

 

Attack Rate Calculation

 

The attack rate was calculated using the number of confirmed cases (14) as the numerator and the total population of Hodan District as the denominator. The population estimate of 164,941 was sourced from census data and local health surveys conducted in the district. This population figure was used to standardize the attack rate to per 100,000 people.

 

Laboratory investigation

 

In this study, laboratory diagnosis used serum sample separated from the whole blood obtained from suspected patients using centrifugation at 1500 × g for 4 min specifically detecting the virus through testing for a virus-produced protein called NS1 and also included the detection of anti-DENV immunoglobulins. The Dengue NS1 immunochromatographic strip test was employed for qualitative detection of NS1 in blood samples, aiding in early diagnosis prior to the presence of IgM or IgG antibodies. This testing was conducted at the National Public Health Reference Laboratory, Somalia.

 

The Standard Q Arbo Panel I (Z/D/C/Y) test -a rapid multiplex immunochromatographic lateral flow assay, was used for detecting IgM to Dengue virus and NS1 antigen. According to the manufacturer's instructions, 10 μL of serum sample was mixed with assay diluent buffer. A positive NS1 test result confirms dengue virus infection, although it does not provide serotype information. In cases of negative NS1 results, SD Biosensor Dengue Dou NS Ag and IgM test kit was used to determine previous or recent dengue exposure.

 

Data analysis procedure

 

Data were cleaned and checked for completeness and accuracy by two independent study personnel. Descriptive statistics (frequencies, percentages) were used to describe both the continuous and categorical variables. Tables, graphs and charts were included to represent the study findings. All data was analyzed using Microsoft Excel (Version 2016).

 

Ethical consideration

 

Ethical clearance was obtained from the National Institute of Health with approval number NIH/IRB/01/SEP/2022. We communicated with the district health officer of the Banadir region about conducting the dengue fever investigation and official permission was obtained from the district health officer (DHO). Additionally, verbal informed consent was obtained from all the participants or their parents/legal guardian which was also approved by the ethics committee of the National Institutes of Health.

 

 

Laboratory confirmation

 

A total of 147 suspected dengue fever cases were reported from Hodan District with the first index case detected on 11 September 2022. Out of 147 suspected cases, 14 cases (9.5%) tested positive for DF virus at the National Public Health Reference Laboratory. The overall attack rate was 89/100,000 with a zero-case fatality rate.

 

Description of cases by persons, place and time

 

Distribution of the Dengue outbreak by personal variables

 

The dengue outbreak investigation started on 20 November 2022 to 18 December 2022. During the investigation period, a total of 147 suspected cases were identified. An attack rate of 89 cases per 100,000 people with zero case fatality rate was reported from Hodan district. The suspected cases had a median age of 9 (interquartile range 2-25) years. The highest number of dengue fever cases was seen in the above 14 years age group with a total of 57 cases with an attack rate of 48/100,000 people. Additionally, the distribution of dengue fever cases was seen more in males with 57% compared to females (Table 1). The attack rate by gender could not be calculated due to lack of discrete population data on total number of males and females in Hodan district.

 

Distribution of the Dengue outbreak by place

 

The outbreak affected sub-sections of Hodan district to varying degrees (Figure 2). Majority of cases were reported from Ka´aan sub-section with 78 dengue cases (53%) followed by Oktobar with 31 dengue cases (21%), and the least number of cases (6%) were reported from Ahmed Gurey sub-section.

 

Distribution of the Dengue outbreak by time variables

 

The Epi curve (Figure 3) showed multiple peaks that indicated a continuing source outbreak. The first dengue fever confirmed case was reported on 11 September 2022 from Ladnan hospital, Hodan district, Banadir region. The first case was identified as a 25-year-old male presenting with an 8-day history of fever, myalgia, joint pain, and maculopapular rash and hemorrhagic manifestations. The case was confirmed in Ladnan hospital with positive IgG and IgM results.

 

As shown in Figure 3, four cases were reported in September, and one dengue case in October. The cases increased to 81 cases in November. Furthermore, a spike of cases was investigated on 29 November with a total of 16 cases recorded that day. Subsequently, there was a decrease in the number of cases in the preceding days. The last case was recorded on 14 December 2022.

 

Distribution of the Dengue outbreak by sign and symptoms variables

 

The dengue case distribution by signs and symptoms in Hodan district, all 147 cases had a fever (100%). Other signs and symptoms were myalgia (88%), joint pain (56%), maculopapular (9%) and hemorrhagic manifestations (1%).

 

Possible risks identified for contracting Dengue

 

Out of 147 cases, only one case had a history of travel to previously affected areas and had exposure with previously known dengue cases. We visited 14 households with confirmed cases. Several mosquito breeding sites were identified in 78% of these households, including discarded tires, plastic bottles, and surrounding man-made stagnant water, which were common in the affected communities. Additionally, there was no proper waste disposal in any of the four sub-sections of the Hodan district. Due to the hot weather in the town, 62% of residents wore short-sleeved clothes and slept outside of their houses, while 85% did not use bed nets, and 80% did not apply mosquito repellents.

 

 

We confirmed a Dengue fever outbreak in Hodan District, Banadir region, Somalia with 14 laboratory confirmed cases out of 147 suspected cases, resulting in a positivity rate of 9.5%. This positivity rate appears lower compared to the 14.7% positivity rate reported in a study conducted in the Banadir region, where Hodan District was among the regions studied [6]. Additionally, the overall attack rate was 89/100,000 with a zero-case fatality rate which is lower than the studies conducted in the Kabridahar District [7], and rural areas of Pakistan [8]. Several factors may have contributed to this low positivity rate, including the timing of sample collection relative to the onset of symptoms, potential misclassification of suspected cases, or the possibility that some cases were caused by other febrile illnesses prevalent in the region. Additionally, our study did not include serotyping, which could have provided more detailed information on the circulating dengue virus serotypes in the district, as different serotypes can have varying levels of virulence and impact on the community. Future studies could benefit from incorporating serotyping to better characterize dengue outbreaks in similar settings.

 

In our study, based on clinical manifestations, fever, myalgia, joint pain, and maculopapular rash were the most reported symptoms, indicative of mild dengue [9]. The current investigation showed that all Dengue fever cases in the Hodan District had fever. This is consistent with the investigation conducted at Dire Dawa city administration[10], Ethiopia, University of Malaya Medical Centre Kuala Lumpur, Malaysia[11]. Only one percent of cases had hemorrhagic manifestations, which is much lower compared to other dengue outbreaks. This minimal occurrence of hemorrhagic complications likely contributed to the zero-case fatality rate.

 

Furthermore, this study indicated that males were more affected than females. A possible explanation could be that men spend most of their time outdoors and wear short-sleeved clothes thus are more at risk for mosquito bites than women who traditionally cover more of their bodies. This finding is consistent with a study conducted in Bihar [12], Eastern India [13], and rural areas of Pakistan [14].

 

The distribution of cases was higher in the Ka´an sub-section of Hodan district, likely due to its proximity to the largest market in the Banadir region. This increases the potential for mosquito transmission from other areas. Additionally, the area is characterized by its population of internally displaced persons and low-socioeconomic families.

 

Although dengue affects all age groups, 90% of cases occur in children under 18 years of age [14]. Our study findings indicate that the highest number of dengue fever cases was observed in the age group above 14 years, consistent with a study conducted in the Werder town region of Ethiopia [15]. In contrast, a higher incidence of dengue in children aged 1 to 14 years was observed in a study conducted in the Banadir region [6].

 

Actions taken

 

The following actions were taken during the investigation period:

 

First, we conducted risk communication and Community Engagement. Community health education was undertaken in all the communities in Hodan district. Various health education initiatives using several modalities were carried out to educate the community about Dengue and the current outbreak. During the outbreak, every subsection of Hodan district health facility workers were trained and assigned the responsibility of educating their family members and neighbors about dengue transmission and prevention modalities. Health education was also delivered to community members through community meetings and house-to-house visits by community health workers (CHWs).

 

Second, we distributed and translated in the local language (Somali) risk communication community materials (handouts, leaflets, brochures etc.) on the early signs of dengue, routes of transmission of dengue and treatment of dengue. This contributed towards increased community awareness of the signs and symptoms of dengue fever.

 

Finally, we shared the Arboviral line list to private hospitals and public health centers to collect detailed information of the cases and to rule out dengue from other febrile illnesses like malaria which share same clinical manifestations.

 

The limitations of this outbreak investigation were first, the inability to run serotype analysis of DENV and investigate the possibility of coinfection. Second, due to the limited knowledge about DF disease transmission and prevention, the hospitals were not familiar with dengue cases hence the underreporting of cases due to health workers diagnosing dengue fever as malaria disease.

 

 

The dengue fever outbreak in Hodan District was confirmed. Community health education was undertaken by distributing risk communication messages on dengue fever to the public. Health workers were sensitized on case definition for dengue and copies of dengue case definition were distributed to the health facilities. To prevent future outbreaks, we recommend controlling mosquito breeding sites, community education and awareness should be prioritized to ensure the public adopts preventive measures, such as using mosquito repellents and properly disposing of waste to control future outbreaks.

 

Recommendations

 

We formulated a number of recommendations based on our findings and conclusion:

• Further entomological studies to be conducted exploring risk factors in depth.
• To improve community surveillance, conduct regular training to enhance the capacity of the health workers to report on dengue fever cases.
• To educate the community about mode of transmission of the vector-borne diseases and to give awareness on effective preventive strategies.
• To provide dengue test kits in every health facility so that high-grade fever patients are confirmed without mistaking them for other febrile illnesses.
• To provide prevention commodities such as mosquito repellents and beds, especially to those at high risks and in IDP camps.

 

 

The author(s) declare that they have no competing interests.

 

 

Conceptualization: SG, AMF; Methodology: SG, AMF; Formal Analysis: SG; Writing-Original Draft Preparation: SG; Writing – Review & Editing: AMF, KSM. All authors have read and agreed to the published version of the manuscript.

 

 

SOM-FETP program, National Institute of Health, Ministry of Health, Somalia, AFENET and sponsors of the program CDC, WHO, PHAS.

 

 

Table 1: Distribution of Dengue cases by Gender, Age group, and clinical symptoms (N=147)

Figure 1: Map of Somalia showing Hodan district, the epicenter of DF outbreak

Figure 2: Distribution of Dengue cases by Sub-section of Hodan District, Sept-Dec 2022

Figure 3: Distribution of Dengue cases by Date of Onset in Hodan district, Sept-Dec 2022

 

 

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