Climate Variability,Urbanization,Water Insecurity,and Cholera in Somalia (2000-2025): A Thematic Narrative Review

Abstract

Background:

Cholera remains endemic in Somalia with epidemic spikes linked to water insecurity, climate variability, and rapid urbanization. This narrative synthesis characterizes epidemiological patterns and structural determinants of cholera transmission.

Methods:

Systematic narrative review following PRISMA guidelines retrieved literature from PubMed, Scopus, Web of Science, and gray sources (WHO, UNICEF, UN-Habitat, Somali Ministry of Health, Water, sanitation, and hygiene (WASH) Cluster) for English-language publications (2000-2025) on cholera epidemiology, water security, and urbanization in Somalia. Thematic synthesis used Thomas and Harden’s inductive framework. Quality appraisal applied CASP checklist for mixed-methods research.

Findings:

Three intersecting determinants drive endemic cholera: (1) chronic water insecurity from recurrent droughts and unsafe informal sources; (2) rapid urbanization and informal settlements without adequate Water, sanitation, and hygiene (WASH) infrastructure; and (3) fragile surveillance systems. Hotspots cluster in riverine districts (Shabelle, Juba) and urban peripheries (Mogadishu, Baidoa). Children under 5 and internally displaced persons experience disproportionate burden. Oral cholera vaccine reduced case fatality rates from 1.5% (2017) to 0.1% to 0.6% (2024-2025), yet endemic transmission persists.

Conclusions:

Cholera control requires integrated multi-sectoral interventions. Priorities include: (1) linking climate and Water, sanitation, and hygiene Water, sanitation, and hygiene (WASH) monitoring; (2) transitioning to climate-resilient piped water infrastructure; (3) formalizing internally displaced person settlements with planned Water, sanitation, and hygiene (WASH) infrastructure; (4) strengthening surveillance and laboratory capacity; and (5) establishing cross-sectoral coordination across health, urban planning, water resources, and climate adaptation.

Plain Language Summary

How Unsafe Water, Crowded Cities and Climate Extremes Keep Cholera Spreading in Somalia, and What Needs to Change By 2030.

Cholera is a severe diarrhoeal disease that can kill within hours if untreated. It is completely preventable when people have safe water, toilets, and good hygiene. Yet in Somalia, cholera has continued to appear almost every year from 2000 to 2025. This review brings together information from scientific articles, UN agencies, and Somali government reports to explain why cholera keeps returning and what must change. We focus on three main issues: lack of safe water, very fast urban growth, and the effects of climate change. Somalia faces repeated droughts and floods. Drought dries up wells and forces families to use a tiny amount of often unsafe water. Later, heavy rains and floods wash human waste into rivers and shallow wells. At the same time, more people are moving into cities and informal camps for displaced people. These crowded settlements often lack piped water, drainage, rubbish collection, and safe toilets. As a result, one sick person’s waste can quickly contaminate the water used by many families, especially children. We also describe how the health system struggles with weak disease surveillance, limited laboratory capacity, and heavy dependence on emergency responses such as water trucking and temporary latrines. Our findings show that treating patients and giving cholera vaccines, while essential, are not enough. To break the cycle, Somalia needs reliable, climate-resilient water systems, safer planned settlements for displaced people, better sanitation, and earlier warning systems that link weather forecasts to cholera risk. Controlling cholera is therefore not only a medical issue but also a question of fair access to basic services and long-term investment in water, sanitation, and urban planning.

Aims and Review Questions

Aims and Objectives

This narrative synthesis aimed to characterize the epidemiological burden of cholera in Somalia from 2000 to 2025 and to synthesize multi-sectoral evidence on the structural, environmental, and climatic factors associated with endemic transmission. The specific objectives were to (1) describe trends in cholera incidence, geographical distribution, and affected populations; (2) examine how water insecurity, climate variability, and Water, sanitation, and hygiene (WASH) infrastructure deficits are linked to cholera transmission risk; (3) analyze the role of rapid urbanization and informal settlement proliferation in amplifying disease vulnerability; and (4) identify evidence-based policy and programmatic priorities for integrated cholera control aligned with GTFCC 2030 targets.

Review Questions

1. What is the epidemiological pattern of cholera in Somalia from 2000 to 2025, and which populations bear the greatest disease burden?

2. How are water insecurity, Water, sanitation, and hygiene (WASH) infrastructure deficits, and climate variability associated with the spatial and temporal distribution of cholera outbreaks?

3. What role does rapid urbanization and the proliferation of informal settlements play in sustaining cholera transmission, and what structural interventions does the evidence support?

Introduction

Cholera, caused by Vibrio cholerae, remains a significant global public health threat, despite the existence of effective preventive and curative interventions. Researchers estimate that between 1.3 and 4.0 million cholera cases and 21 000 to 143 000 deaths occur annually worldwide, ¹ although officially reported figures to the World Health Organization (WHO) substantially underestimate the true burden. ² The disparity between estimated and reported cases reflects limited surveillance capacity, inadequate laboratory confirmation, and underreporting driven by the fear of economic and tourism consequences. ² Approximately 1.3 to 1.4 billion people living in endemic countries remain at risk of infection, with approximately 99% of reported cases occurring in South Asia and Africa, regions where water, sanitation, and hygiene Water, sanitation, and hygiene (WASH) infrastructure is chronically inadequate. ³

The epidemiology of cholera is fundamentally shaped by the Water, sanitation, and hygiene (WASH) conditions and access to safe water. Vibrio cholerae is transmitted through the consumption of contaminated food or water, ⁴ and thrives in aquatic ecosystems where sanitation infrastructure is poor or absent. ⁵ Communities lacking piped-water systems, improved sanitation facilities, and adequate hygiene education have a substantially elevated risk of infection. ⁶ Beyond biomedical transmission, the persistence of cholera reflects profound structural inequities; every case is preventable with existing tools, yet the disease remains endemic in populations experiencing poverty, weak governance, and limited infrastructure investment. ³ Therefore, understanding cholera in endemic settings requires examination of interconnected water security, sanitation systems, urbanization patterns, and climate dynamics.

Somalia exemplifies the complex interplay among these factors. The country has experienced uninterrupted cholera transmission from 2000 to 2025 with recurring epidemic spikes driven by drought-induced water scarcity, flood-triggered contamination, and conflict-related displacement. ⁷ Somalia’s climate is predominantly arid and semi-arid, with more than 90% of the land classified as water-scarce; the nation’s population is entirely dependent on intermittent and highly variable rainfall. ⁸ Between 2000 and 2025, Somalia experienced 5 major drought cycles, most severely the 2020 to 2023 drought affecting 7.8 million people, followed by devastating 2023 to 2024 flooding that displaced over 700 000 persons and inundated 1.5 million hectares of farmland. ⁹ These climate shocks are linked to predictable oceanic drivers, including the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). ³ Climate projections indicate an increasing frequency and intensity of both droughts and heavy rainfall events, intensifying water insecurity and flood risk. ¹⁰

Water scarcity forces populations to rely on shallow, unprotected wells and contaminated surface water from rivers (Shebelle, Juba), reducing per capita water availability below hygiene thresholds and severely limiting handwashing practices. ⁷ Approximately 70% of boreholes and hand-dug wells exceeded the WHO salinity threshold of 1500 µS/cm, with fluoride contamination affecting 65% of the tested wells. ⁸ During drought periods, emergency water trucking, which is operationally necessary, introduces secondary contamination risks; unchlorinated tanker water frequently contains Escherichia coli, and cost spikes force vulnerable households to return to unsafe riverine sources. ¹¹ Conversely, intense rainfall events trigger urban flooding that saturates pit latrines and contaminates shallow wells through fecal-oral pathways, amplifying the transmission risk. ⁷ Only 38% of Somalis have access to basic sanitation and 28% practice open defecation, ensuring that climate shocks rapidly convert chronic water and sanitation deficits into acute epidemic risk. ⁷

Rapid urbanization has fundamentally reshaped Somalia’s demographic and epidemiological landscapes. Urban populations have grown from approximately 24% of the national population in 2000 to 45% by 2020, with projections reaching 54% by 2025.^12,13 This urbanization has been driven by relative urban peace, recurrent climate-induced rural displacement, and conflict-related population movements. ¹⁴ Consequently, approximately 2.6 million internally displaced persons (IDPs), representing approximately 17% of the total population, are concentrated in urban centers, such as Mogadishu, Kismayo, and Garowe. ¹⁴ These settlements are predominantly informal and are located on private land without tenure security; approximately 85% lack formal municipal planning, creating extreme population density and minimal sanitation infrastructure. ¹³ IDP settlements face chronic exclusion from piped water systems; residents depend on expensive, unregulated water vendors or unsafe wells. ¹⁵ The absence of functional drainage systems means that heavy rainfall inundates poorly constructed pit latrines, mixing raw sewage with floodwaters and contaminating water sources across densely populated districts. ¹⁶ This constellation of high-density, inadequate Water, sanitation, and hygiene (WASH) access, and extreme weather vulnerability positions informal urban settlements as persistent reservoirs for Vibrio cholerae transmission.

Somalian disease surveillance and health system capacity are severely constrained. The International Health Regulations (IHR) compliance score is 31 out of 100, with fewer than 0.4 health workers per 10 000 population. ⁷ The Integrated Disease Surveillance and Response (IDSR) system, established in 2020 to 2021, operates at a capacity of only 30%, rendering cholera outbreak detection and response highly fragile. ⁷ Laboratory confirmation is severely limited; during the 2023 Banadir cholera outbreak, only 25 stool samples were tested, undermining epidemiological precision. ¹⁷ Oral cholera vaccine (OCV) campaigns have reached over 1.2 million persons annually since 2017, reducing case fatality rates from 1.5% in 2017 to approximately 0.1% to 0.6% in 2024 to 2025. ¹⁷ However, endemic transmission persists, suggesting that vaccination alone cannot interrupt transmission without complementary Water, sanitation, and hygiene (WASH) and water-security interventions.

A comprehensive understanding of cholera epidemiology in Somalia requires an integrated examination of water insecurity, urbanization dynamics, and health system capacity. Multiple narrative and systematic reviews have addressed cholera epidemiology in sub-Saharan Africa^2,18and water-sanitation links to waterborne diseases, ⁶ and individual studies have documented cholera outbreaks in Somalia.^7,14 However, no comprehensive synthesis of Somali evidence has systematically integrated epidemiological data with environmental, urbanization, and structural health system factors to characterize how water insecurity, the Water, sanitation, and hygiene (WASH) infrastructure, rapid urbanization, and climate dynamics are interconnected drivers of endemic cholera transmission. This synthesis addresses this gap by bringing together peer-reviewed literature, surveillance reports, and technical documents from the WHO, UNICEF, UN-Habitat, and the Somali Ministry of Health to construct a coherent evidence base for policy and programmatic action.

Methods

Study Design

This narrative review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for narrative reviews (Figure A1). ¹⁹ Narrative design permits a broad investigation of interconnected themes (water scarcity, urbanization, Water, sanitation, and hygiene (WASH) infrastructure, climate variability, and cholera epidemiology) across heterogeneous study types and temporal/geographical contexts, which is appropriate for understanding complex system-level drivers in fragile health settings.

Data Sources and Search Strategy

The literature was systematically retrieved from 3 peer-reviewed bibliographic databases: PubMed (via MEDLINE), Scopus, and Web of Science. Searches were conducted from 20- Nov-205 to 26-Nov-2025, covering English-language publications from January 2000 to December 2025. Gray literature was supplemented by authoritative international organizations such as the World Health Organization (WHO), United Nations Children’s Fund (UNICEF), UN Habitat, Federal Ministry of Health (Somalia), Water, sanitation, and hygiene (WASH) Cluster, and International Organization for Migration (IOM).

The search terms combined Medical Subject Headings (MeSH) and keywords through Boolean operators across 4 conceptual domains:

• Cholera: “cholera” OR “Vibrio cholerae” OR “acute watery diarrhea” OR “AWD”

• Water Security: “water scarcity” OR “water access” OR “water supply” OR “Water, sanitation, and hygiene (WASH)” OR “water sanitation hygiene”

• Urbanization: “urbanization” OR “urban settlement” OR “informal settlement” OR “IDP” OR “internally displaced person*”

• Geography: “Somalia” OR “Somali region” OR “Horn of Africa”

Example search string (PubMed):(cholera OR “Vibrio cholerae” OR “acute watery diarrhea”) AND (Water, sanitation, and hygiene (WASH) OR “water sanitation” OR “water scarcity” OR “water access”) AND (Somalia OR “Somali region” OR “Horn of Africa”)

Similar searches were adapted for Scopus and the Web of Science. Gray literature searches used organizational websites and document repositories.

Study Selection

The inclusion Criteria: Peer-reviewed journal articles, government health ministry reports, WHO, UNICEF, World Bank, and humanitarian organization publications (2000-2025) that provided empirical data on the following:

• Cholera incidence, prevalence, epidemiological trends, or outbreak investigations in Somalia or comparative African contexts

• Water access, water quality, sanitation infrastructure, or Water, sanitation, and hygiene (WASH) coverage in Somalia

• Urbanization patterns, settlement characteristics, or internally displaced person populations in Somalia

• Health system capacity, surveillance systems, or disease response in Somalia

Exclusion Criteria:

• Non-peer-reviewed sources (Wikipedia, ResearchGate, Academia.edu)

• Opinion editorials without empirical data

• Publications in languages other than English

• Research unrelated to cholera, water/sanitation, urbanization, or Somalia

Two independent reviewers screened the titles and abstracts using standardized eligibility criteria and resolved disagreements through consensus or consultation with a third reviewer. Full-text articles that met the inclusion criteria underwent a detailed examination.

Data Extraction

Data were extracted using a standardized form capturing:

• Bibliographic information (author, year, publication type)

• Geographic focus (country, subnational region)

• Study design and population

• Key findings on cholera epidemiology, water security, Water, sanitation, and hygiene (WASH) infrastructure, urbanization, and health system response

• Outcome measures and effect estimates (where applicable)

Quality Appraisal

The included studies underwent quality assessment using the Critical Appraisal Skills Programme (CASP) checklist adapted for mixed-methods research. The domains evaluated included the clarity of research aims, methodological appropriateness, study design rigor, data collection validity, analysis transparency, and relevance of findings. Studies scoring lower on quality criteria were noted but included in the synthesis, with appropriate weighting in narrative integration to acknowledge limitations in surveillance and observational data from fragile health systems.

Thematic Synthesis

The data synthesis followed the inductive thematic synthesis framework proposed by Thomas and Harden in 3 iterative stages.

1. Initial coding: Line-by-line coding of study findings to identify concepts, themes, and relationships relevant to water security, Water, sanitation, and hygiene (WASH), urbanization, climate variability, and cholera transmission.

2. Descriptive theme development Concepts were organized into descriptive themes across key dimensions: (i) water access and infrastructure, (ii) sanitation and hygiene practices, (iii) population displacement and urbanization dynamics, (iv) climate variability and seasonality, (v) health system capacity and surveillance, and (vi) cholera epidemiology and disease burden.

3. Analytical synthesis: Analytical themes were constructed to explain how water insecurity, urbanization dynamics, climate variability, and health system fragility intersect to shape cholera transmission patterns in Somalia. Thematic patterns, contradictions, and evidence gaps were integrated into a coherent narrative to address review questions.

Study Characteristics

Figure 1.

Figure 1.

PRISMA 2020 flow diagram of study selection for the narrative review.

Results

Cholera Epidemiology and Disease Burden in Somalia (2000-2025)

Cholera has remained endemic to Somalia throughout the 2000 to 2025 period, with uninterrupted transmission and recurrent epidemic spikes. ²⁰ The most significant outbreak occurred in 2017, when over 78 000 suspected cases and 1159 deaths were reported, corresponding to a case fatality rate (CFR) of 1.5%. ²¹ Following a period of lower transmission, cholera resurgence was documented in 2023 and 2024, with 18 304 and 21 944 suspected cases, respectively, with a CFR of approximately 0.6%. ¹⁷ By August 2025, the WHO reported an additional 7484 suspected cases and 9 deaths, indicating ongoing endemic transmission at a lower intensity. ¹⁷

Spatial analysis revealed cholera hotspots concentrated in riverine districts along the Shabelle and Juba rivers (Beletweyne, Kismayo, and Jowhar) and urban peripheries, particularly the Banadir region (Mogadishu). ¹⁷ Children under 5 years of age consistently account for over 50% of confirmed cases and associated mortality, a burden exacerbated by malnutrition. ¹⁷ Internally displaced people (IDPs) in overcrowded settlements with minimal Water, sanitation, and hygiene (WASH) infrastructure experience disproportionately high attack rates. ¹⁷ Epidemiological trends show a strong temporal association between cholera incidence and climate anomalies, with outbreaks frequently following El Niño-induced flooding and prolonged drought. ¹⁷ Oral cholera vaccine (OCV) campaigns have reached over 1.2 million persons annually since 2017, contributing to a reduction in CFRs from 1.5% in 2017 to approximately 0.1% to 0.6% in 2024 to 2025. However, persistent endemic transmission despite vaccination suggests that structural water and sanitation interventions are essential complements to immunization for sustainable control. ¹⁷

Water Insecurity as an Epidemiological Driver

Water insecurity fundamentally underpins the risk of cholera in Somalia. The nation’s arid and semi-arid climate renders the population dependent on intermittent rainfall; more than 90% of the land is classified as water scarce. ⁸ Between 2000 and 2025, Somalia experienced 5 major drought cycles, most severely the 2020 to 2023 drought affecting 7.8 million people. ⁹ Groundwater is the primary drinking water source outside the Juba and Shabelle River basins; however, approximately 70% of boreholes and hand-dug wells exceed the WHO salinity threshold of 1500 µS/cm, with fluoride contamination affecting 65% of the tested wells. ⁸ Salinity issues stem from evaporitic geological formations, seawater intrusions in coastal zones, and prolonged drought-induced concentrations of dissolved minerals. ⁸

Drought-induced water scarcity forces populations to rely on shallow, unprotected wells and contaminated surface water from rivers, where Vibrio cholerae persists as an aquatic organism. ⁵ Studies indicate that drought-driven reductions in per capita water availability below hygiene thresholds severely limit handwashing practices and increase the risk of fecal-oral transmission. ²² Emergency water trucking, while operationally necessary, introduces secondary contamination; unchlorinated tanker water frequently tests positive for Escherichia coli, and cost spikes during crises force vulnerable households to return to unsafe riverine sources.^11,23

WASH Infrastructure Deficits and Transmission Pathways

National water, sanitation, and hygiene (WASH) coverage is critically inadequate. Only 41.1% of Somali households utilized improved sanitation facilities, ¹² and approximately 28% practiced open defecation. ²⁰ The drought-flood cycle amplifies the transmission pathways. During flash floods, surface runoff washes fecal matter from open defecation sites into shallow aquifers and surface bodies of water. ¹¹ Inadequate sanitation infrastructure, particularly the absence of functional latrines in displacement camps, prevents safe waste containment. Extreme weather events breach these minimal systems and saturate water points. ²⁰ In riverine districts along Juba and Shabelle, the absence of functional drainage systems means that heavy rainfall inundates pit latrines, mixing raw sewage with floodwaters and contaminating shallow wells used for drinking water. ¹⁶ Consequently, the convergence of poor water quality, insufficient latrine coverage, and climate-driven flooding sustains persistent Vibrio cholerae transmission corridors across Somalia. ²⁰ Only 38% of the population has access to basic sanitation, ensuring that climatic shocks rapidly convert chronic infrastructure deficits into an acute epidemic risk. ²⁰

Rapid Urbanization and Informal Settlements: Structural Vulnerability

Somalia’s urbanization rate is one of the fastest in the world. Urban populations have grown from approximately 24% in 2000 to 45% by 2020, with projections reaching 54% by 2025.^12,13 This urbanization has been driven by relative urban peace, recurrent droughts and floods, and conflict-related displacements. ¹⁴ Consequently, approximately 2.6 million IDPs, representing approximately 17% of the total population, are concentrated in urban centers such as Mogadishu, Kismayo, and Garowe. ¹⁴

Approximately 85% of IDP sites are informal, located on private land without tenured security, and lack formal municipal planning. ¹³ These settlements are characterized by extreme overcrowding, lack of tenure security, and absence of basic services, creating densities that facilitate rapid disease transmission.^13,14 Informal settlements are systematically excluded from municipal water grids, and piped water connections are almost non-existent in many IDP zones. ¹⁵ Residents depend on expensive, unregulated water vendors or unsafe shallow wells. ²⁴ Households without access to treated municipal water face significantly elevated odds of cholera acquisition as they are forced to consume water from sources directly compromised by inadequate drainage and sewage overflow. ¹⁵

The absence of functional drainage systems in peripheral zones indicates that heavy rainfall inundates poorly constructed latrines, causing raw sewage to contaminate floodwaters and shallow wells across densely populated districts. ¹⁶ This creates a “fecal-oral“ transmission cycle that is sustained by the continued reliance on contaminated water sources. The failure of municipal waste management to reach informal settlements generates persistent reservoirs of Vibrio cholerae that resurge during each rainy season. ¹⁷

Climate Variability, Drought-Flood Cycles, and Epidemic Amplification

Somalia’s climate is characterized by highly unpredictable rainfall patterns and strong sensitivity to oceanic drivers, including the El Niño-Southern Oscillation (ENSO), Western V Gradient, and Indian Ocean Dipole. ¹ The country has experienced 8 failed rainy seasons since 2010. ¹ Climate projections indicate an increasing frequency and intensity of extreme rainfall and temperatures, compounding water scarcity, and flood risk. ¹⁰

Between 2024 and 2025, Somalia endured its worst drought in approximately 40 years, triggered by 4 consecutive failed rainy seasons (April-June and October-December). ⁸ This prolonged drought created acute water scarcity affecting approximately 6.4 million people, with boreholes becoming non-functional and traditional water sources drying up. ⁹ Communities were forced to rely on expensive and often contaminated trucked water, intensifying the transmission risk. ²⁰

The drought-flood paradox further exacerbates vulnerability; while droughts deplete water sources and concentrate contaminants, sporadic intense rainfall triggers devastating floods that contaminate water sources, destroy sanitation infrastructure, and displace populations. ⁹ The 2023 Deyr floods exemplified this pattern, causing over 17 000 cholera cases as floodwaters breached the sanitation infrastructure in the Banadir and Hiraan regions. ¹⁷ Epidemiological trends reveal a strong temporal correlation between cholera incidence and climate anomalies; outbreaks frequently follow El Niño-induced flooding and prolonged droughts, with water disruptions jeopardizing safe water access and contaminating the environment with Vibrio cholerae. ¹⁷

Health System Capacity and Surveillance Constraints

Somalian disease surveillance and response capacity are severely constrained, limiting the ability to detect and respond to cholera outbreaks. International Health Regulations (IHR) compliance was assessed at 31 out of 100, with fewer than 0.4 health workers per 10 000 population. ⁷ The Integrated Disease Surveillance and Response (IDSR) system, established in 2020 to 2021, operates at a capacity of only 30%. ⁷ Laboratory confirmation capacity is severely limited; during the 2023 Banadir outbreak, only 25 stool samples were tested, substantially limiting the epidemiological precision. ¹⁷

Real-time reporting through an Early Warning Alert and Response System (EWARS) has been implemented; however, coverage remains geographically patchy, especially in remote and conflict-affected areas. ²⁰ Coordination among government, non-governmental organizations (NGOs), and United Nations (UN) actors shows inconsistent data sharing and resource allocation. ⁷

Integrated Pathways: How Water Insecurity, Urbanization, and Climate Intersect in Cholera Transmission

Cholera outbreaks in Somalia have emerged from intersecting vulnerabilities that create predictable transmission cascades. Prolonged droughts precipitate mass rural-to-urban displacement, forcing populations into overcrowded informal settlements that lack basic water and sanitation infrastructure. ¹⁷ Water scarcity forces reliance on shallow wells and river sources contaminated with Vibrio cholerae, while inadequate sanitation facilities sustain fecal-oral transmission cycles. ²⁰ Conversely, intense rainfall events trigger urban flooding that collapses fragile drainage systems, inundating pit latrines and contaminating surface water across densely populated districts. ¹⁶

The 2023 Deyr floods illustrate this cascade: floodwaters breached sanitation infrastructure in peripheral urban zones, causing over 17 000 cholera cases in Banadir and Hiraan. ¹⁷ These dynamics operate within the baseline of endemic Water, sanitation, and hygiene (WASH) deficits: only 38% of Somalis have access to basic sanitation and 28% practice open defecation, ²⁰ ensuring that climate shocks rapidly convert chronic risk into acute epidemics. The convergence of water insecurity, inadequate sanitation, high population density in informal settlements, and climate-driven extreme events thus creates a sustained transmission system in which Vibrio cholerae circulates continuously, with outbreak magnitude driven by climatic variations and population displacement.

Discussion

Summary of Key Findings

This narrative synthesis examined the epidemiological, environmental, and structural evidence of cholera transmission in Somalia from 2000 to 2025. Three intersecting determinants have emerged as linked to endemic cholera: (1) chronic water insecurity driven by an arid climate, recurrent droughts, and dependence on unsafe informal water sources; (2) rapid urbanization and proliferation of informal settlements lacking adequate Water, sanitation, and hygiene (WASH) infrastructure, generating high-density, high-transmission environments; and (3) fragile health surveillance systems with limited laboratory capacity and weak integration of climate and water resource monitoring with disease response. Spatial hotspot clusters in riverine and urban peripheries. Children under 5 years of age and IDPs bear a disproportionate disease burden. While oral cholera vaccination reduced case fatality rates, endemic transmission persisted, indicating that structural Water, sanitation, and hygiene (WASH) and water security interventions are essential.

Comparison With Broader Literature

These findings align with the regional and global evidence on cholera epidemiology in water-insecure, rapidly urbanizing contexts. Systematic reviews of cholera in sub-Saharan Africa have similarly documented the primacy of Water, sanitation, and hygiene (WASH) infrastructure deficits and water insecurity as epidemiological drivers.^2,18 Global analyses emphasize the role of climate variability in triggering spike outbreaks in endemic zones.^5,10 The literature on informal urban settlements in low-income countries documents systematically elevated waterborne disease risk due to high density, limited sanitation, and exclusion from municipal services. ¹³

However, this synthesis contributes to novel integration of Somali-specific evidence. While prior reviews examined individual drivers (cholera epidemiology, urbanization, or Water, sanitation, and hygiene (WASH)), this analysis characterizes the interconnected temporal and spatial dynamics by which water insecurity, rapid urbanization, and climate variability jointly sustain endemic transmission. The emphasis on drought-flood cyclicity-rather than static “water scarcity”-reflects the actual climate dynamics driving Somali epidemiology and has not been emphasized in prior regional reviews. Additionally, the documentation of surveillance underreporting and laboratory capacity limitations provides granular evidence of the detection gaps underlying reported case figures, illuminating the gap between the estimated and officially reported cholera burden in Somalia.

Evidence Quality and Limitations

However, this synthesis has several limitations. Surveillance data from fragile health systems are subject to substantial under-reporting, particularly in inaccessible rural and conflict-affected zones. Laboratory confirmation capacity is severely limited; the 2023 Banadir outbreak tested only 25 stool samples, meaning that most cases were suspected rather than confirmed, potentially biasing estimates of disease burden. ¹⁷ The synthesis included heterogeneous study types (peer-reviewed publications, gray literature from humanitarian organizations, surveillance reports) with varying methodological rigor. While quality appraisal was applied, observational and cross-sectional designs cannot establish causal inference, and the lack of quantitative meta-analysis limits the precision of effect estimates.

Gray literature bias is possible; published peer-reviewed articles may differ systematically from unpublished surveillance reports in focus, geographic scope, or case definitions. No randomized trials or prospective cohort studies specifically examining water interventions in Somalia were identified; evidence of intervention effectiveness derives from regional studies in other contexts, potentially limiting local applicability. Narrative synthesis, while appropriate for complex system-level questions, does not quantify the relative contribution of individual determinants (water insecurity vs urbanization vs climate) to cholera transmission; this decomposition would require quantitative modeling or multivariate analysis, which is not possible with available data.

Additionally, data on certain determinants-particularly the prevalence of specific Water, sanitation, and hygiene (WASH) practices in IDP settlements and the quantitative relationship between piped water access and cholera incidence in Mogadishu-are sparse and rely on indirect inference from aggregate statistics. The review was limited to English-language literature, potentially missing important contributions in other languages. Finally, surveillance data are concentrated in urban areas and accessible regions, and the true disease burden in remote and conflict-affected zones may be substantially underestimated.

Strengths and Contributions of This Review

Despite these limitations, this study has several strengths. It systematically searched multiple databases and gray literature sources, adhering to the PRISMA guidelines for narrative synthesis and applying standardized quality appraisal. Inductive thematic synthesis using Thomas and Harden’s framework permitted the identification of emergent themes and patterns not driven by preconceived theoretical models. The focus on Somalia, a specific, severely affected country with distinct climate and urbanization dynamics, provides actionable details relevant to national and international stakeholders.

Critically, this synthesis explicitly integrates epidemiological data with environmental and structural evidence, moving beyond the siloed examination of individual drivers, to characterize how water insecurity, urbanization, and climate variability interact dynamically to shape transmission patterns. The documentation of drought-flood cyclicity as a key mechanism distinguishes this analysis from prior work that focuses on static water scarcity. The synthesis also clearly highlights surveillance and laboratory capacity gaps, quantifying the detection limitations that underlie reported case counts and demonstrating why surveillance improvements are critical cholera control interventions.

Implications for Practice and Policy

The convergence of chronic water insecurity, rapid informalization of urban settlements, and fragile surveillance systems indicates that cholera control in Somalia cannot succeed through health sector interventions alone. Vaccination campaigns have measurably reduced severe outcomes, but have not interrupted endemic transmission, demonstrating the necessity of complementary structural interventions. Public health authorities should prioritize integrated, multi-sectoral interventions.

1. Integration of climate and Water, sanitation, and hygiene (WASH) monitoring: Linking hydrometeorological forecasts (ENSO and rainfall anomalies) to cholera hotspot mapping and preparedness triggers can enable proactive outbreak responses aligned with predicted high-risk periods.

2. Transition from emergency to sustainable water systems: Emergency water trucking, while operationally necessary during acute crises, perpetuates dependence on expensive, contaminated supplies, and diverts resources from durable piped water infrastructure. Medium-term investment in climate-resilient water systems in endemic districts (Baidoa, Kismayo, and Beletweyne) is essential.

3. Formalization of IDP settlements: Permanent rather than temporary shelter, combined with planned Water, sanitation, and hygiene (WASH) infrastructure, reduces transmission risk and provides equity in access to municipal services.

4. Strengthening surveillance and laboratory capacity: The expansion of stool sample collection and laboratory confirmation (starting with hotspot districts) improves outbreak detection and enables antimicrobial resistance monitoring and serotype characterization.

5. Multi-sectoral coordination: Health, urban planning, water resource management, and climate adaptation sectors must align their budgets and accountability mechanisms. Siloed responses perpetuate the cyclical pattern of reactive humanitarian interventions, without structural improvement.

Implications for Practice and Policy

The findings indicate that cholera control in Somalia requires coordinated, multi-sectoral action extending beyond health-sector interventions alone. While oral cholera vaccination has reduced case fatality rates, sustained transmission reflects persistent structural vulnerabilities related to water insecurity, inadequate sanitation infrastructure, rapid urbanization, and weak surveillance systems. Evidence supports prioritizing climate-informed preparedness, gradual transition from emergency water provision to resilient piped systems, planned upgrading of informal settlements with integrated WASH services, and strengthening laboratory-confirmed surveillance in endemic districts. Detailed operational and implementation-oriented recommendations are provided in Annex 1.

Implications for Future Research

Future research should include:

1. Quantitative modeling linking specific Water, sanitation, and hygiene (WASH) interventions (piped water, latrine coverage, hygiene promotion) to cholera incidence in Somali contexts, enabling evidence-based prioritization of investments.

2. Prospective surveillance studies in IDP settlements are needed to characterize contamination pathways, identify population-level water and sanitation risk factors, and enable real-time detection and response.

3. Climate-epidemiology analysis uses satellite-derived rainfall data, oceanic indices (ENSO and IOD), and surveillance data to quantify the lead time between climate anomalies and outbreak peaks, enabling predictive modeling.

4. Qualitative research on barriers to and enablers of Water, sanitation, and hygiene (WASH) practice change, water source choice, and health-seeking behavior in urban poor and IDP populations informing behavior change communication strategies.

5. Health economics analysis of the cost-benefit of sustained Water, sanitation, and hygiene (WASH) investment versus repeated humanitarian emergency response provides business case evidence for long-term financing models.

Conclusion

Cholera persistence in Somalia from 2000 to 2025 reflects structural vulnerabilities driven by chronic water insecurity, rapid urbanization with inadequate WASH infrastructure, and fragile surveillance capacity. Climate-driven drought–flood cycles intensify transmission by disrupting water access and contaminating sanitation systems, particularly in informal urban settlements hosting large internally displaced populations. Although oral cholera vaccination has reduced case fatality rates, endemic transmission persists, underscoring that vaccination alone is insufficient without sustained investments in safe water, sanitation infrastructure, and surveillance systems. Achieving cholera control aligned with Global Task Force on Cholera Control targets will require integrated, multi-sectoral action linking climate adaptation, urban planning, water resource management, and public health surveillance.