Sri Lanka is facing a signicant dengue outbreak in 2026, fueled by heavy rains, the onset of the southwest monsoon, and widespread ooding since mid-May. Case numbers climbed sharply from 25,082 in early May to nearly 92,854 by 18 August, marking roughly a 600% increase over the same period last year. The National Dengue Control Unit (NDCU) recorded more than 7,500 new cases in August alone, prompting concern over a potential epidemic. The outbreak was concentrated in the Western, Southern, North Western, Sabaragamuwa, and Central provinces, with the Western Province accounting for nearly half of all cases nationwide and Colombo District alone representing 55.1% of the national total.
During Week 32, Colombo recorded 747 cases, followed by Gampaha (759) and Kalutara (257), with notable numbers also reported in Matara, Kandy, Ratnapura, Galle, Kurunegala, Jana, and Kegalle. On 8 June, a three-day nationwide mosquito control campaign was launched, covering 14 districts and 72 Medical Ocer of Health divisions, alongside strict enforcement measures including "red notice" warnings for properties harboring mosquito breeding sites. In response, the Simplied Early Action Protocol was initially activated on June 3, 2026, covering 23 high-risk zones across ve districts: Colombo, Gampaha, Kalutara, Kandy, and Jana. With the additional 35 highrisk zones identied within the same districts where the sEAP was active, there was an urgent need to expand the intervention throughout the sEAP districts, particularly as the dengue outbreak had spread beyond the originally identied high-risk zones during the sEAP preparedness phase.
Dengue cases in Sri Lanka surged to their highest levels in July. Data from the National Dengue Control Unit (NDCU) as of mid-August 2026 shows that July marked the worst month of the outbreak, with 29,964 cases reported. During mid-July, weekly suspected cases consistently exceeded 7,300 across the country. Overall, the July surge brought the cumulative 2026 caseload to over 92,000, with 69 dengue-related deaths and a case fatality rate of 0.07%.
The geography of the outbreak also shifted: Gampaha district overtook Colombo as the most aected district nationally (13,795 versus 19,068 cases as of 18 August), while the Western Province's overall share eased slightly to around 52.6–52.8% as the Southern Province's contribution grew to roughly 15.6–15.7%, indicating a redistribution of burden rather than a national slowdown. A new and concerning development emerged in mid-July: A cluster of 71 cases, including ve hospitalizations, was identied among University of Colombo students in July, prompting the University of Moratuwa and the University of the Visual and Performing Arts to temporarily close their campuses—the rst institutional clusters recorded in this outbreak.
Separately, disease-monitoring analysis (BEACON) agged that the escalation thresholds it had set out on 3 July had since been breached: high-risk MOH divisions had expanded well beyond the 124 threshold, the case fatality rate had climbed above the historical 0.05% baseline, and case counts had shown no decline through July. Analysts noted that Gampaha's rise to the top of the case burden was signicant given documented insecticide resistance in local Aedes aegypti and Ae albopictus populations, implying that fogging and adulticide measures may be delivering diminishing returns exactly where the burden is now heaviest. The sharp spike in July matches Sri Lanka’s typical post-monsoon dengue pattern, as rainwater creates ideal breeding sites for Aedes mosquitoes. The decline in August is likely due to the rapid rollout of the national "Stop Dengue Now" program, greater community awareness, and targeted surveillance in high-risk areas.
Dengue cases remain highly concentrated in a few areas. During July and August, the Western Province accounted for 52% to 56% of all cases nationwide. Gampaha and Colombo are the national epicenters, mainly due to high population density and urban infrastructure. Kandy is the most aected area outside the Western Province. Other key districts with ongoing transmission include Matara, Kalutara (5,964 cases), Galle (5,063 cases), and Ratnapura (4,946 cases).
The cases over 92,000 recorded by 18 August had already surpassed full-year totals from recent endemic years, including 2025's 51,000 cases, and at the prevailing rate of about 1,100 cases per day, a 100,000-case total was projected to be reached by end-August — well before the October–December northeast monsoon peak — putting the 2019 epidemic total of 105,049 cases within plausible range for the current season alone. The analysis identied the August–September inter-monsoon trough, during which incidence has historically declined, as the critical factor determining whether the health system enters the next monsoon season already saturated.
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