Dengue Returns to Guam: The First Local Cases Since 1944

On September 9, 2019, a Guam resident with no travel history developed a dengue-like illness. The next day the Guam Public Health Laboratory found dengue virus type 3 (DENV-3) in the patient’s blood — the island’s first locally acquired dengue case since 1944.

A fast response

• September 11: the Guam Department of Public Health and Social Services began enhanced surveillance and alerted every health care provider on how to get patients tested.
• September 13: the Government of Guam declared a state of emergency.

Teams visited homes within 656 feet (200 m) of where each confirmed local case lived — handing out information, searching for more cases, removing mosquito breeding sites, setting mosquito traps and applying pesticide where residents agreed. Billboards, pamphlets and sessions in schools and communities spread the word, and hospitals, medical societies and most clinics were briefed on caring for dengue patients.

The outbreak

A suspected case was a feverish Guam resident with at least two of: muscle aches, headache, joint pain, eye pain, rash or bleeding signs. A confirmed case needed laboratory proof.

From September 9 to November 25, officials identified 249 suspected cases:

• 213 had PCR testing at the island’s lab; private labs off the island ran antibody tests for 124
• 17 (7%) were confirmed — 13 locally acquired and 4 linked to travel
• 11 local cases were confirmed as DENV-3 by PCR, and 2 by antibody testing

Local cases fell ill between September 3 and November 11. Their median age was 12 (range under 1 to 67), 62% were male, and two were hospitalized. Cases clustered in the more densely populated north and center of the island.

Suspected and confirmed dengue cases on Guam by date of symptom onset, 2019. Image from CDC’s report.

Why it happened now

Dengue outbreaks are common in the Pacific Islands; DENV-3 was then spreading in the Marshall Islands, Palau, the Philippines and Yap. Guam sees imported cases almost every year: 42 from 1988 to 2018 and 3 more in 2019 before the outbreak — all 45 linked to travel, most often from the Philippines (69%).

The 1944 outbreak was spread by the mosquito Aedes aegypti. After it, and a Japanese encephalitis outbreak in 1947, the U.S. military ran extensive mosquito control that eradicated A. aegypti from Guam. Surveys now find no A. aegypti — but they do find Aedes albopictus, another mosquito that can carry dengue. The 2019 outbreak shows that dengue can spread locally on Guam, most likely through A. albopictus.

Lessons

Future preparedness for mosquito-borne viruses on Guam must close the gaps in detection and response that dengue’s return exposed.

Sources

Based on Kern-Allely S, Pobutsky A, Hancock WT, "Notes from the Field: First Evidence of Locally Acquired Dengue Since 1944 — Guam, 2019," MMWR Vol. 69, No. 13, CDC, with the passage cut off in the imported copy completed from the same report in PubMed Central (PMC7119517); a work of the United States government in the public domain.