Dengue Fever Outbreak in Hawaii First in 50 Years

By Andrew Ten Have, MD, MPH

KAILUA-KONA, Hawaii (Reuters Health) - The Hawaii Department of Health (DOH) is warning all Hawaiian physicians to be on the alert for possible dengue fever cases, in response to the first documented local transmission of the virus in Hawaii since 1943.

As of October 8, the CDC has confirmed 34 cases of dengue in residents of the rural, wet, mosquito-prone region of East Maui. There are roughly 100 additional suspected cases in Maui at this time, with laboratory confirmation pending. Although Hawaii DOH officials are also working up several suspected cases on Oahu, Hawaii and Kauai, the outbreak is currently limited to East Maui, affecting mostly residents in the rural towns of Hana and Nahiku.

In addition, 27 cases of dengue fever were reported prior to September 20 in Hawaii, but these early cases were in individuals who recently traveled to Asian and Pacific countries where the disease is currently epidemic.

The current outbreak is historically unusual because the incidence of the infection is increasing among residents who have no history of recent travel and also because the Aedes Aegypti mosquito has not been seen in Hawaii since it was supposedly eradicated by pesticide spraying in 1943.

According to the CDC, Hawaii's Asian tiger mosquito, or Aedes albopictus, is not an ``efficient'' carrier of the virus. The Aedes Aegypti mosquito is thought to be the natural carrier of the virus and is the prevalent mosquito in epidemic areas outside of Hawaii. A CDC entomologist is currently on-site in East Maui investigating these issues.

A large dengue fever epidemic is now sweeping across Asia and the Pacific, with approximately 8,000 cases reported in the Philippines, 4,000 cases in Malaysia and 1,000 cases in Singapore, all reported in the first half of 2001, with less than half these numbers reported in all of 2000. According to Dr. Philip Bruno, chief of the Hawaii DOH Communicable Diseases Division, the Hawaii outbreak appears to be an extension of the Asia-Pacific epidemic, which is almost inevitable as travelers go back and forth between Hawaii and countries like the Philippines.

In an interview with Reuters Health, Bruno said, ``East Maui is an ecological niche in Hawaii; it is a fairly lush and isolated region that uniquely sustains transmission of the virus back and forth between mosquito and human. This eco-environment is found in only a few other places in Hawaii. In addition, the Hawaiian Aedes albopictus mosquito should inhibit the spread of an epidemic. For these reasons, we feel that the Hawaii outbreak will not extend to a large number of people or get out of control, and will remain mild in comparison to the large epidemic affecting other tropical areas.''

The Hawaii DOH has responded to the outbreak with an aggressive mosquito control and eradication campaign in East Maui, community education efforts and an October 2 warning to all Hawaii physicians.

Life-threatening complications of dengue are rare but can be severe, especially in second infections with another type of the virus. There are four types of dengue fever virus, and unfortunately immunity to one does not confer immunity to the others.

The most severe epidemics are occurring in tropical areas that are now experiencing a second wave of infection with a new type of dengue fever virus. All confirmed cases in the Maui outbreak have been uncomplicated and have not required hospitalization.

According to Bruno, a small number of travelers have contracted the infection while visiting Maui, while the great majority of travelers have not. Nevertheless, Bruno advises mainland physicians to consider dengue fever as a possible diagnosis in any traveler experiencing fever, plus two other dengue fever signs or symptoms, such as rash, headache or joint pain. Travel must have been completed within 2 weeks of onset of illness, to either Hawaii or other countries where dengue fever is epidemic (most of East Asia and the Pacific basin).

Travelers to these tropical areas, including East Maui, are advised to wear long-sleeved shirts and long pants, to use mosquito repellents containing 20% to 30% DEET on any exposed skin and to wear light-colored clothing, as mosquitoes are attracted to dark colors. Travelers are also advised to avoid outdoor activities that increase their risk of infection, such as camping in mosquito-infested areas of East Maui.