Story highlights 25 residents and 8 visitors, including 4 children, diagnosed with dengue fever since September

This is the first outbreak of dengue fever on Hawaii's Big Island

Kona Ironman participants asked to notify the Hawaii Department of Health if they have fever and two additional symptoms

(CNN) More than eight million tourists flock to the Hawaiian islands every year. Those packing their bags need to be sure to pack mosquito repellant.

That's because state health officials are investigating a cluster of dengue fever. Thirty-three people on Hawaii's Big Island have become sick with the mosquito-borne disease since September, according to Hawaii state health officials . This is the first locally transmitted outbreak of the viral illness on the Big Island and the first outbreak in the state since five people were infected on the island of Oahu in 2011

Twenty-five of those infected in this current outbreak are residents of the Big Island, while eight are visitors. Four children are among those who have become ill. All patients have recovered or are recovering.

The most recent case was identified on November 2. The first patient began exhibiting symptoms on September 11.

Dengue is transmitted to humans when they are bit by infected mosquitoes.

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