State Department of Health officials reported four more cases of dengue fever Thursday, bringing the total to 19 on Hawaii island.

The increase came as vector control crews worked to contain the outbreak of locally acquired dengue by spraying insecticide to kill virus-carrying mosquitoes outside the homes in the area of those who have fallen ill.

Meanwhile, a person living in Kalama Valley on Oahu was suspected of contracting dengue fever while in Southeast Asia, prompting a visit by health officials to some residents in that neighborhood.

Officials said the Kalama Valley visit was unrelated to the outbreak on the Big Island and is done as a routine precaution. Test results related to the Kalama Valley case are still pending, and vector control workers found no mosquito larvae in the area of the person’s dwelling, said Health Department spokeswoman Janice Okubo.

Hawaii County officials kept Hookena Beach in South Kona closed after several cases of dengue were connected to people who had visited the area.

Dr. Melissa Viray, deputy state epidemiologist for Hawaii, said the state is continuing to investigate how the disease came to the Big Island.

Officials said the outbreak began Sept. 15, and people were probably infected five to seven days before symptoms set in.

State health officials announced the first Hawaii island dengue fever cases Oct. 29.

Symptoms can include a fever, joint or muscle pains, headache or pain behind the eyes, and a rash.