Background: Dengue Fever (DF) is a viral disease primarily transmitted by Aedes (Ae.) aegypti mosquitoes. Outbreaks in Eastern Ethiopia were reported during 2014–2016. In May 2017, we investigated the first suspected DF outbreak from Kabridahar Town, Somali region (Eastern Ethiopia) to describe its magnitude, assess risk factors, and implement control measures. Methods: Suspected DF cases were defined as acute febrile illness plus ≥2 symptoms (headache, fever, retro-orbital pain, myalgia, arthralgia, rash, or hemorrhage) in Kabridahar District residents. All reported cases were identified through medical record review and active searches. Severe dengue was defined as DF with severe organ impairment, severe hemorrhage, or severe plasma leakage. We conducted a neighborhood-matched case-control study using a subset of suspected cases and conveniently-selected asymptomatic community controls and interviewed participants to collect demographic and risk factor data. We tested sera by RT-PCR to detect dengue virus (DENV) and identify serotypes. Entomologists conducted mosquito surveys at community households to identify species and estimate larval density using the house index (HI), container index (CI) and Breteau index (BI), with BI≥20 indicating high density. Results: We identified 101 total cases from May 12–31, 2017, including five with severe dengue (one death). The attack rate (AR) was 17/10,000. Of 21 tested samples, 15 (72%) were DENV serotype 2 (DENV 2). In the case-control study with 50 cases and 100 controls, a lack of formal education (AOR [Adjusted Odds Ratio] = 4.2, 95% CI [Confidence Interval] 1.6–11.2) and open water containers near the home (AOR = 3.0, 95% CI 1.2–7.5) were risk factors, while long-lasting insecticide treated-net (LLITN) usage (AOR = 0.21, 95% CI 0.05–0.79) was protective. HI and BI were 66/136 (49%) and 147 per 100 homes (147%) respectively, with 151/167 (90%) adult mosquitoes identified as Ae. aegypti. Conclusion: The epidemiologic, entomologic, and laboratory investigation confirmed a DF outbreak. Mosquito indices were far above safe thresholds, indicating inadequate vector control. We recommended improved vector surveillance and control programs, including best practices in preserving water and disposal of open containers to reduce Aedes mosquito density.

Yellow fever (YF) is a viral hemorrhagic fever, endemic in the tropical forests of Africa and Central and South America. The disease is transmitted by mosquitoes infected with the yellow fever virus (YFV). Ethiopia was affected by the largest YF outbreak since the vaccination era during 1960–1962. The recent YF outbreak occurred in 2013 in Southern part of the country. The current survey of was carried out to determine the YF seroprevalence so as to make recommendations from YF prevention and control in Ethiopia. A multistage cluster design was utilized. Consequently, the country was divided into 5 ecological zones and two sampling towns were picked per zone randomly. A total of 1643 serum samples were collected from human participants. The serum samples were tested for IgG antibody against YFV using ELISA. Any serum sample testing positive by ELISA was confirmed by plaque reduction neutralization test (PRNT). In addition, differential testing was performed for other flaviviruses, namely dengue, Zika and West Nile viruses. Of the total samples tested, 10 (0.61%) were confirmed to be IgG positive against YFV and confirmed with PRNT. Nine (0.5%) samples were antibody positive for dengue virus, 15(0.9%) forWest Nile virus and 7 (0.4%) for Zika virus by PRNT. Three out of the five ecological zones namely zones 1, 3 and 5 showed low levels (< 2%) of IgG positivity against YFV. A total of 41(2.5%) cases were confirmed to be positive for one of flaviviruses tested. Based on the seroprevalence data, the level of YFV activity and the risk of a YF epidemic in Ethiopia are low. However additional factors that could impact the likelihood of such an epidemic occurring should be considered before making final recommendations for YF prevention and control in Ethiopia. Based on the results of the serosurvey and other YF epidemic risk factors considered, a preventive mass vaccination campaign is not recommended, however the introduction of YF vaccine in routine EPI is proposed nationwide, along with strong laboratory based YF surveillance.

Acute respiratory infections because of respiratory syncytial viruses (RSVs) are among the major leading causes of morbidity and mortality in children worldwide. RSV prevalence and its contributing factors among children aged under 5 years in Ethiopia are not well studied. To assess the prevalence and associated factors of RSV infection in children aged under 5 years using influenza sentinel surveillance sites in Ethiopia. A cross-sectional study design was used utilizing influenza-like illness/sever acute respiratory illness surveillance data from January 2021 to December 2022 at the Ethiopian Public Health Institute. In total, 2234 cases were included, with an overall RSV positivity rate of 16.2%. The RSV positivity rate was high in children aged under 1 year (22.8%) and during fall season (24.8%). The RSV positivity rate was significantly associated with ages under 1 year (adjusted odds ratio [AOR] 2.8, 95% confidence interval [CI]: 1.89-4.15) and 1-2 years (AOR 1.9, 95% CI: 1.26-2.73) and the fall season (AOR 1.67, 95% CI: 1.17-2.38). The study revealed that a considerably high RSV positivity rate was detected in children aged under 5 years. The age of children and season have a significant association with RSV positivity rate. Further studies of RSV viral genotype, clinical characteristics, and disease outcome need to be conducted for a better understanding of the virus and disease outcome.

SARS-CoV-2 co-infection with the influenza virus or human respiratory syncytial virus (RSV) may complicate its progress and clinical outcomes. However, data on the co-detection of SARS-CoV-2 with other respiratory viruses are limited in Ethiopia and other parts of Africa to inform evidence-based response and decision-making. We analyzed 4,989 patients’ data captured from the national severe acute respiratory illness (SARI) and influenza-like illness (ILI) sentinel surveillance sites over 18 months period from January 01, 2021, to June 30, 2022. Laboratory specimens were collected from the patients and tested for viral respiratory pathogens by real-time, reverse transcription polymerase chain reaction (RT-PCR) at the national influenza center. The median age of the patients was 14 years (IQR: 1–35 years), with a slight preponderance of them being at the age of 15 to less than 50 years. SARS-CoV-2 was detected among 459 (9.2%, 95% CI: 8.4–10.0) patients, and 64 (1.3%, 95% CI: 1.0–1.6) of SARS-CoV-2 were co-detected either with Influenza virus (54.7%) or RSV (32.8%) and 12.5% were detected with both of the viruses. A substantial proportion (54.7%) of SARS-CoV-2 co-detection with other respiratory viruses was identified among patients in the age group from 15 to less than 50 years. The multivariable analysis found that the odds of SARS-CoV-2 co-detection was higher among individuals with the age category of 20 to 39 years as compared to those less than 20 years old (AOR: 1.98, 95%CI:1.15–3.42) while the odds of SARS-CoV-2 co-detection was lower among cases from other regions of the country as compared to those from Addis Ababa (AOR:0.16 95%CI:0.07–0.34). Although the SARS-CoV-2 co-detection with other respiratory viral pathogens was minimal, the findings of this study underscore that it is critical to continuously monitor the co-infections to reduce transmission and improve patient outcomes, particularly among the youth and patients with ILI.

Chickenpox is a highly contagious viral infection caused by varicella-zoster virus (VZV) whose clinical manifestations mimic mpox posing challenges for diagnosis without laboratory confirmation. Here, we investigated VZV among the mpox-suspected cases, May to October 2022, in Ethiopia. Samples were collected from 202 mpox-suspected cases in 11 of Ethiopia’s 14 regions and screened for mpox virus by real-time polymerase chain reaction (RT-PCR). Then, differential testing of other selected orthopoxviruses, VZV and herpes simplex virus (HSV) were conducted for 133 randomly selected samples. Whole-genome sequencing (WGS) and downstream analysis was performed on 8 VZV-positive samples. Descriptive statistics were used to summarize epidemiological and clinical data. All the 202 enrolled cases tested negative for mpox. Of these, 133 samples were tested for VZV, and 107 (80.5%, 95% CI: 72.9% – 86.3%) turned positive but remained negative for HSV and other tested orthopoxviruses. At least one VZV-positive case was reported in each region sampled. Half (49.6%) of the cases were hospitalized, with no fatalities. The sequences were clustered primarily in Clade 5 (62.5%, 5) followed by Clade 3 (25.0%, 2) and Clade 1 (12.5%, 1). This investigation confirmed VZV as the predominant causative agent among mpox-suspected cases. To our knowledge, this represents the first clade-level genomic characterization of VZV from Ethiopia, revealing circulation of multiple clades among samples collected during May to October 2022. The findings highlight the need to strengthen differential diagnostic capacities including multiplex testing, and building genomic surveillance capacities for epidemic intelligence and outbreak response.

Data in Ethiopia on the epidemiology of Respiratory Syncytial Virus (RSV) and subtypes among influenza-like illness (ILI) and severe acute respiratory infections (SARI) cases is limited. Here, we assessed the epidemiology of RSV and its subtypes among the pediatric and adult ILI /SARI cases in Ethiopia. We conducted prospective, multicenter facility-based study from May 2023 to April 2024. Respiratory swab specimens, epidemiological and clinical data were collected from participants of all age groups, and both hospitalized and non-hospitalized individuals who met the World Health Organization (WHO) case definition for ILI/SARI and provided informed consent. Laboratory investigation was performed using reverse transcription polymerase chain reaction (RT-PCR). Data were analyzed using SPSS V29. Descriptive statistics were used to summarize frequencies and ratios, and multivariable logistic regression model was employed to assess factors associated with RSV positivity. In total, 4170 participants were enrolled, the majority (57.9%) of whom were cases from children under five and SARI (76.5%). RSV was detected in 654 cases (15.7%; 95% CI: 14.6–16.8). RSV subtyping was carried out for 475 (72.6%) of 654 RSV positive samples. The finding revealed that both RSV-A and RSV-B subtypes were co-circulating in Ethiopia, with predominance of RSV-B (68.8%). Age group, season and timing of sample collection were factors independently associated with RSV positivity. Accordingly, children aged < 2 years (AOR: 8.20, 95% CI: 3.57–18.81) and 2–4 years (AOR: 5.01, 95% CI: 2.15–11.67), autumn (AOR: 5.89, 95% CI: 3.79–9.17) and winter (AOR: 3.27, 95% CI: 2.07–5.16) seasons, and case whose samples were collected within three days of symptom onset (AOR: 1.76, 95% CI: 1.09–2.84) were significantly associated with RSV positivity. The study provides evidence of RSV circulation among ILI/SARI cases in Ethiopia. It also revealed that RSV-B was the predominant subtype circulating in the country. The age-specific and temporal patterns of RSV positivity identified in this study contribute to the understanding of RSV and its subtypes epidemiology in Ethiopia. The findings provide valuable evidence to inform implementation of RSV vaccine introduction programs, particularly targeting high-risk populations during periods of peak transmission. Future research focusing on RSV genomic analysis and disease burden is needed to better understand RSV viral evolution, transmission dynamics and public health impacts in Ethiopia.