The Centers for Disease Control and Prevention’s Dengue Branch, working out of San Juan, reported on May 14 that 3,798 dengue cases were identified in the U.S. states and the District of Columbia during 2024, a 359 percent increase over the 2010–2023 annual average of 828 cases. The figures, published in the Morbidity and Mortality Weekly Report by Sandra J. Kiplagat and colleagues (MMWR, Vol. 75, No. 18, pages 227–233), are surveillance data, not modeling: each case is a laboratory-confirmed or probable infection reported through the national arboviral surveillance system, ArboNET. Of the 3,798 cases, 3,693 (97.2 percent) were travel-associated and 105 (2.8 percent) were locally acquired. Six patients died, all of them returning travelers with severe dengue, for a case-fatality rate of 0.2 percent. Hospitalization was reported for 36.1 percent of cases.
The 2024 total is the highest U.S. count in the 14 years the dataset covers, and the trajectory tracks the regional one. The Pan American Health Organization’s end-of-year situation report for the Americas, covering epidemiological weeks 1 through 52 of 2024 and published January 16, 2025, recorded 13,063,434 dengue cases and 8,431 deaths across the region — the highest annual figure since PAHO began collecting dengue data in 1980 and roughly three times the 2023 regional total. Brazil alone accounted for 10,266,017 of those cases, with Argentina, Mexico, and Colombia next in volume. The four dengue serotypes (DENV-1 through DENV-4) circulated simultaneously across at least nine countries in the region during the year.
Where the U.S. cases came from, and who they were
The MMWR analysis breaks down the 3,693 travel-associated cases by country of likely exposure. The three leading sources named in the Discussion were Mexico (892 cases, 25.4 percent), Cuba (633 cases, 18.1 percent), and India (225 cases, 6.4 percent). Locally acquired cases were reported from three states only: Florida (85 cases across 10 counties), California (18 cases across three counties), and Texas (two cases in two counties). Puerto Rico is reported separately under the U.S. territories surveillance line and is not included in the 3,798 figure; the territory’s own 2024 dengue numbers are tracked by the Puerto Rico Department of Health in coordination with the CDC Dengue Branch.
The demographic breakdown carries the usual caveats of surveillance data, but two figures are worth naming. About 21.8 percent of cases occurred in adults aged 50–59, the largest single age group, with the next-largest cohorts in adults aged 40–49 and 60–69. And 57.5 percent of all cases were among Hispanic or Latino persons; among the 105 locally acquired cases, the share rose to 66.7 percent. The MMWR authors note that this distribution reflects, in part, travel patterns between the United States and dengue-endemic countries in the Caribbean and Latin America, where travel by U.S. residents with family or community ties to those regions is concentrated. The surveillance data do not, on their own, support a claim about underlying susceptibility differences between groups.
The Los Angeles County cluster, as the closest look at local transmission
The most detailed published account of a 2024 U.S. locally acquired cluster appeared in CDC’s Emerging Infectious Diseases journal in May 2026 (Vol. 32, No. 5), by Aisling M. Vaughan and colleagues at the Los Angeles County Department of Public Health. Between August and November 2024, the county identified 14 locally acquired dengue cases across six neighborhoods (designated A through F) in the broader Los Angeles area. Eight of the 14 cases sat in a single neighborhood in the central San Gabriel Valley, and six of those eight occurred within a one-mile radius over a seven-week period; the investigators characterized that sub-cluster as consistent with an outbreak involving ongoing local transmission. The remaining six cases were spread across five additional neighborhoods, with neighborhood B roughly 37 miles from neighborhood A at the maximum span, and were treated by investigators as multiple independent introductions from returning travelers rather than a single seeded chain. Serotype information was available for 11 of the 14 patients: DENV-3 in eight, DENV-1 in one, and indeterminate as either DENV-1 or DENV-3 in two. Aedes aegypti mosquitoes were collected near case residences, but no DENV-positive mosquitoes were detected in the surveillance trapping that followed. The vector was present; the virus, in the trapped samples, was not.
During 2024, a record 3,798 dengue cases were reported, representing a 359% increase above the 2010–2023 annual average. — Sandra J. Kiplagat and colleagues, CDC Dengue Branch, MMWR 75(18):227–233, May 14, 2026
What the data say, and where the inference has to stop
Three drivers are commonly cited for the regional dengue increase: warmer and wetter conditions that expand the seasonal range and breeding window of Aedes aegypti and Aedes albopictus, the post-2020 rebound in international travel volume between the United States and Latin America and the Caribbean, and concurrent large outbreaks in source countries that raise the probability any given traveler is infected. The MMWR surveillance summary documents the U.S. case totals and the country-of-exposure distribution. It does not attempt to attribute the increase to any single driver, and the present reporting does not either: the 2024 dataset can characterize who got sick and where they were exposed, but the relative weight of climate, travel volume, and source-country epidemic intensity in producing the 359 percent jump is a separate analytical question, and one the MMWR authors do not answer.
What the surveillance data do support is a narrower point about the U.S. response posture. Locally acquired transmission requires a competent local vector, an infectious imported case in the right place at the right time, and a window in which the mosquito can bite and pass the virus. The 105 locally acquired cases in 2024 were concentrated in three states where Aedes aegypti is established and where vector-surveillance and mosquito-control programs sit at the county and mosquito-control-district level — Miami-Dade, Hillsborough, and Manatee counties in Florida; Los Angeles, San Diego, and Long Beach jurisdictions in California; the lower Rio Grande Valley in Texas. CDC’s dengue surveillance page (accessed May 18, 2026) describes routine state-level surveillance as the primary mechanism for detecting and responding to local transmission. The capacity for that detection varies by jurisdiction, and the Los Angeles County investigation, which ran multi-agency entomological and clinical surveillance for four months, is an instance of what a well-resourced response looks like.
What to track
Three specifics are worth following in named sources. The CDC Dengue Branch’s ArboNET-derived weekly case counts for 2026, posted to the agency’s dengue surveillance pages, are the running U.S. total and will be the first place a sustained shift above the 2024 trajectory shows up. PAHO’s weekly dengue situation reports for the Americas (the most recent at this writing covers epidemiological week 14, 2026) carry the regional comparator. And the next MMWR cycle on 2025 U.S. surveillance, expected in the second quarter of 2026, will indicate whether the 2024 figure was a single-year peak driven by the regional outbreak or the new operating baseline. The locally acquired column is the one to watch in either case. It is the smaller number now, and the leading indicator if it changes.