Epidemiological, Clinical, and Diagnostic Characteristics of a Large-Scale Upsurge of Dengue in the Rohingya Refugee Camps and Host Communities in Coxs Bazar, Bangladesh, 2021 to 2024: A Retrospective Study

This retrospective study of 35,581 RDT-confirmed dengue cases in Coxs Bazar (2021–2024) reveals a large-scale, sustained upsurge predominantly affecting Rohingya refugees, characterized by seasonal peaks, high pediatric burden, and specific predictors of severe disease, underscoring the urgent need to shift from episodic outbreak responses to integrated, long-term preparedness strategies in humanitarian settings.

The Gist

Imagine a crowded neighborhood where thousands of people are living in makeshift shelters, like a giant, temporary city built from bamboo and tarps. In this place, a new, invisible enemy arrived in 2021: Dengue fever, a mosquito-borne virus that causes high fevers and severe pain.

This paper is like a detailed detective report written by a team of health investigators (mostly from the International Organization for Migration) who watched this enemy grow over four years (2021–2024) in the Rohingya refugee camps in Cox's Bazar, Bangladesh. They wanted to understand how the virus behaved, who it hurt the most, and how to stop it.

Here is the story of their findings, broken down simply:

1. The Enemy's Growth Spurt

When the virus first arrived in late 2021, it was like a small spark. But by 2022, it had exploded into a massive fire.

• The Numbers: They tracked over 35,000 confirmed cases. That's a huge crowd of sick people!
• Who got sick? Most were refugees (90%), but the local neighbors (host communities) got sick too.
• The Pattern: The virus loves the rainy season (monsoon). Think of the rain as a "green light" for mosquitoes. Every year, the sickness peaked during the rains, but the timing shifted slightly later each year, and the "tail" of the sickness lasted longer. It wasn't just a one-time burst anymore; it was becoming a permanent resident.

2. The "Who" and "Why"

The investigators looked at who was getting hit hardest:

• The Young and Old: While children (under 14) made up nearly half the cases, the older adults (60+) were in the most danger of needing to stay in the hospital.
• Men vs. Women: More men got sick than women. The researchers guess this is because men often spend more time outside working or socializing, putting them in the "line of fire" for mosquito bites.
• The Danger Zone: The biggest risk factors for ending up in a hospital bed were:
  • Waiting too long to see a doctor.
  • Having other health problems (like diabetes or heart issues).
  • Having specific "warning signs" like severe stomach pain or low blood pressure.

3. The "Detective Work" (Diagnosis)

The paper explains a tricky game of "hide and seek" between the virus and the tests used to find it.

• The Early Game (NS1 Test): If you get sick and go to the doctor immediately (within the first 2 days), the virus is still wearing a bright red coat (NS1 antigen). The test sees it easily.
• The Late Game (IgM Test): If you wait 5 or more days, the virus takes off the red coat and puts on a blue one (IgM antibodies). If the doctor only looks for the red coat, they might miss the patient!
• The Lesson: You need both types of tests available. If you rely on only one, you'll miss a huge chunk of sick people, especially those who arrive late.

4. The Good News and The Bad News

• The Good News: The death rate was incredibly low (less than 0.1%). This is like saying out of 1,000 people who got sick, only one died. Why? Because the health teams set up a great safety net. They had clinics everywhere, community workers who checked on patients daily, and clear rules for when to send people to the hospital.
• The Bad News: The virus isn't going away. It's shifting from a "sudden storm" to a "constant drizzle." The conditions in the camps (crowded living, stagnant water, poor drainage) are like a mosquito paradise. As long as these conditions exist, the virus will keep coming back, year after year.

5. The Big Takeaway: Changing the Strategy

The authors argue that we need to stop treating Dengue like a firefighter (who only shows up when there's a fire) and start treating it like a security guard (who is there every day, watching for trouble).

The New Plan:

• Stop waiting for the outbreak: Instead of reacting when cases spike, we need constant monitoring.
• Clean up the nest: You can't just kill mosquitoes; you have to drain the stagnant water and fix the trash systems where they breed.
• Better Tests: Make sure every clinic has both the "Red Coat" and "Blue Coat" tests so no one is missed.
• Speed is Key: Teach the community to come to the doctor fast. The longer you wait, the more likely you are to get seriously sick.

In a nutshell: This paper tells us that in these crowded refugee camps, Dengue has moved in for the long haul. To win the battle, the community needs to stop playing catch-up and start building a permanent shield of clean water, constant surveillance, and fast medical care.

Technical Summary

1. Problem Statement

Dengue fever emerged as a significant public health threat in the Rohingya refugee camps in Cox's Bazar, Bangladesh, starting in October 2021. Despite the presence of over 1.1 million refugees living in overcrowded, resource-limited conditions with poor sanitation and water management, there was a critical lack of evidence regarding the epidemiology, clinical presentation, and diagnostic patterns of dengue in this specific protracted humanitarian setting. Previous studies focused on urban or national settings in Bangladesh, leaving a gap in understanding how dengue behaves in displacement camps. The study aimed to characterize the transmission dynamics, clinical severity, and diagnostic profiles of the massive upsurge to inform future outbreak preparedness and response strategies.

2. Methodology

• Study Design: Retrospective observational study.
• Setting: Rohingya refugee camps and host communities in Ukhiya and Teknaf Upazilas, Cox's Bazar, Bangladesh.
• Data Source: Anonymized surveillance data from the International Organization for Migration (IOM) dengue patient database.
• Study Population: All individuals diagnosed with dengue across 36 IOM-supported health facilities (22 health posts, 12 primary healthcare centers, and 2 integrated infectious disease treatment centers) between October 1, 2021, and December 31, 2024.
• Case Definition:
  • Suspected: Acute febrile illness.
  • Confirmed: Positive for NS1 antigen or IgM via Rapid Diagnostic Test (RDT).
• Data Analysis:
  • Descriptive Statistics: Summarized demographics, clinical features, and outcomes.
  • Epidemiological Modeling: Weekly incidence was modeled using phase-specific Poisson regression to determine growth and decay rates, doubling times, and halving times for epidemic phases (2021–2024).
  • Predictive Modeling: Multivariable logistic regression was used to identify predictors of inpatient admission and to analyze the association between presentation delay and RDT positivity patterns (NS1 vs. IgM), adjusting for age and sex.

3. Key Contributions

• Scale: This is the largest documented dengue outbreak in a refugee or displacement setting globally, analyzing over 35,000 confirmed cases.
• Epidemiological Transition: The study provides evidence that dengue in Cox's Bazar has shifted from episodic outbreaks to sustained, year-round transmission with endemic characteristics.
• Diagnostic Timing: It establishes a clear correlation between the delay in seeking care and the type of RDT positivity (NS1 vs. IgM), offering critical guidance for diagnostic protocols in humanitarian settings.
• Risk Stratification: It identifies specific demographic and clinical predictors for severe outcomes (inpatient admission) in a refugee population, highlighting the vulnerability of older adults, those with comorbidities, and those presenting late.

4. Key Results

Epidemiological Characteristics

• Caseload: 35,581 RDT-confirmed cases.
  • 90.2% were Rohingya refugees; 9.8% were host community members.
• Trends: Cases increased annually from 1,011 (2021) to a peak of 12,149 (2024).
• Seasonality: Peaks occurred during the monsoon/post-monsoon period (weeks 25–38).
• Transmission Dynamics:
  • Growth rates decreased over time (doubling time increased from 1.54 weeks in 2021 to 7.61 weeks in 2024).
  • Decay rates remained relatively consistent (halving time ~4.4–6.0 weeks), indicating prolonged epidemic tails.
  • The epidemic peak shifted later each year, suggesting a shift in transmission dynamics.

Demographics

• Median Age: 17 years (IQR 7–30).
• Age Distribution: 46.0% of cases were children (0–14 years).
• Sex: 54.4% Male, 45.6% Female.
• Location: 85.0% of cases in Ukhiya, 14.8% in Teknaf.

Clinical Characteristics & Outcomes

• Severity:
  • 8.0% required inpatient admission.
  • 10.1% presented with WHO warning signs (Group B).
  • 0.4% classified as severe dengue (Group C).
  • Case Fatality Rate (CFR): <0.1% (4 deaths reported).
• Symptoms: Most common were fever (50.2%), headache (58.7%), and malaise (55.1%). Notably, atypical symptoms were frequent, including cough (30.8%) and gastrointestinal issues (nausea, vomiting, abdominal pain).
• Predictors of Inpatient Admission (Multivariable Analysis):
  • Age: Older age significantly increased risk (≥60 years: aOR 2.31).
  • Delay: Each day of delay in presentation increased admission risk (aOR 1.06/day).
  • Clinical Signs: Presence of WHO warning signs (aOR 26.60) and low systolic BP (aOR 2.84).
  • Comorbidities: Chronic co-morbidities increased risk six-fold (aOR 6.07).
  • Population: Refugees had higher odds of admission than host community members (aOR 1.39).
  • Sex: Males had lower odds of admission than females (aOR 0.88).

Diagnostic Patterns

• RDT Positivity:
  • NS1 Antigen only: 62.1% (Median delay: 2 days).
  • IgM/IgG only: 33.6% (Median delay: 5 days).
  • Dual Positivity: 4.3% (Median delay: 4 days).
• Delay Correlation: Longer delays from symptom onset were strongly associated with IgM-only positivity. Relying solely on NS1 testing would miss a significant portion of cases presenting later in the illness course.

5. Significance and Policy Implications

The study concludes that dengue in Cox's Bazar is no longer a short-term outbreak but a sustained endemic threat requiring a paradigm shift in response strategies.

• From Outbreak Response to Sustained Preparedness: Health systems must move from reactive, episodic interventions to year-round surveillance, vector control, and resource allocation.
• Integrated Diagnostics: Health facilities must stock both NS1 antigen and IgM/IgG RDTs. Relying only on NS1 will lead to missed diagnoses in patients presenting after day 5, which is common in humanitarian settings due to delayed care-seeking.
• Community Engagement: Reducing the delay in presentation is critical. Strengthening community-based referral systems and risk communication is essential to prevent progression to severe disease.
• Targeted Monitoring: High-risk groups (elderly, those with comorbidities, and refugees) require specific monitoring and early intervention protocols.
• Vector Control: Environmental management (stagnant water removal, waste management) remains the primary prevention strategy, given the high correlation between stagnant water and transmission.

This research provides a foundational evidence base for humanitarian organizations and the Bangladesh government to design long-term, integrated dengue control programs in protracted displacement settings.