Short Sleeves and Work Outdoors Drove a Dengue Outbreak in Northern Yemen

Dengue fever has long been endemic in Yemen, but a cluster of suspected cases in a remote northern district has now given researchers a rare, detailed look at what actually fuels an outbreak in a fragile, conflict-affected setting. When surveillance officers in Amran governorate noticed a surge of suspected dengue in Harf Sufyan district in early September 2023, a rapid investigation team was dispatched within days. The resulting case-control study, published in BMC Infectious Diseases, confirms the outbreak and pinpoints two strikingly simple risk factors: wearing short-sleeved clothing and working outdoors.

The investigation began on September 5, 2023, just one day after the surveillance officer in Amran governorate reported an increased number of suspected dengue fever cases in Harf Sufyan. A joint team from Yemen’s electronic Integrated Disease Early Warning System, known as eIDEWS, and the Rapid Response program traveled to the district to confirm whether an outbreak existed, determine its risk factors, and recommend control measures. Their work offers a technical template for outbreak response in one of the world’s most challenging public health environments.

The team conducted a descriptive case-control study in Harf Sufyan from September 5 to October 29, 2023, using a 1:2 matching ratio. Cases were defined according to the standard World Health Organization case definition of dengue fever, while controls were any person living in the same area whose house was adjacent to the homes of cases and who had not developed dengue fever. Data were collected on individual, environmental, and behavioral risk factors. Attack rates, odds ratios, and confidence intervals were calculated, with a p-value below 0.05 considered statistically significant.

Laboratory confirmation strengthened the descriptive picture. A total of 34 patients tested positive for dengue fever IgM antibodies, and 68 controls were enrolled. Males made up 58 percent of the confirmed cases, and 43 percent were younger than 30 years of age. The overall attack rate was 0.9 per 100 of the population. The first case fell in epidemiological week 37 of 2023, and the outbreak reached its peak in week 39, a compressed epidemic curve typical of explosive dengue transmission in a susceptible population.

Multivariate analysis cut through the noise of dozens of candidate exposures. Only two factors remained significantly associated with dengue infection after adjustment: wearing shorts and T-shirts, which carried an odds ratio of 17 with a confidence interval of 4.8 to 60.1, and working, which carried an odds ratio of 23 with a confidence interval of 2.9 to 33.2. In practical terms, people who wore short-sleeved clothing were roughly 17 times more likely to be infected, and those who worked were roughly 23 times more likely, than their neighbors who did not share those exposures.

The biological logic behind these findings is straightforward. Dengue virus is transmitted by Aedes mosquitoes, principally Aedes aegypti, which bite during daytime hours and preferentially attack exposed skin. Short sleeves and T-shirts leave forearms and legs uncovered, maximizing the surface area available to a day-biting vector. Outdoor work places people in the open during the very hours when Aedes aegypti is most active, multiplying the number of potential infective bites. In Harf Sufyan, where many residents labor in fields and open-air workplaces, the combination of exposed skin and occupational daytime presence created ideal conditions for rapid viral amplification.

The demographic profile of the outbreak adds context. With males comprising a majority of cases and nearly half of patients under 30, the epidemic pattern mirrors the working-age structure of the exposed population rather than any special vulnerability of children or the elderly. An attack rate of 0.9 per 100 may sound modest, but in a district with limited health infrastructure, even a small proportion of clinically ill patients can overwhelm primary care facilities, particularly when dengue can progress to severe dengue, dengue hemorrhagic fever, or dengue shock syndrome in a minority of infections.

The authors conclude that dengue fever is emerging as an important disease in Harf Sufyan district of Amran governorate. Occupational exposure and wearing short-sleeved clothing were identified as the primary significant risk factors, a finding with immediate operational value. Because the protective behavior is as simple as covering more skin, the study recommends increasing community awareness about dengue infection, its mode of transmission, and control measures, along with the use of protective clothing. Such messaging can be delivered through existing community networks without costly equipment or pharmaceutical intervention.

The broader significance of the study extends beyond a single district. Yemen’s health system has been battered by years of conflict, and the eIDEWS and Rapid Response infrastructure demonstrated here shows that even under strain, rapid outbreak confirmation and analytic epidemiology remain feasible. The case-control design, executed with a 1:2 ratio and standard WHO case definitions, produced actionable odds ratios within weeks of the initial alert. For other districts in the Eastern Mediterranean Region where dengue is expanding, the Yemeni experience suggests that vector-borne risk assessment should focus on daytime occupational exposure and clothing coverage as first-line behavioral targets.

For a virus with no specific antiviral treatment and a vaccine landscape still uneven in endemic countries, behavioral prevention remains the backbone of dengue control. The Harf Sufyan outbreak, confirmed through 34 IgM-positive cases and dissected through multivariate analysis, distilled that backbone into two measurable exposures. As dengue continues its global expansion into new territories, the lesson from northern Yemen is that the fight against the virus can begin with something as ordinary as a long-sleeved shirt and as fundamental as recognizing who, in a community, faces the greatest daytime exposure to the mosquitoes that carry it.

Subject of Research: Epidemiology

Article Title: Risk factors associated with dengue fever outbreak in Harf Sufyan district-Amran governorate, Yemen, 2023: case control study

Article References: Al-Marrani, W., Alyusfi, R., & Ghaleb, Y. (2026). Risk factors associated with dengue fever outbreak in Harf Sufyan district-Amran governorate, Yemen, 2023: case control study. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14690-9

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14690-9

Keywords: dengue fever, Yemen, outbreak investigation, case-control study, Aedes aegypti, risk factors, public health, vector-borne disease, Risk, factors, associated, dengue