The state Health Department is investigating five syphilis cases in West Hawaii, the highest number of cases reported on Hawaii island in the past five years.

"It’s an unusual count," said Luke Hasty, program coordinator of the department’s STD/AIDS Prevention Branch. "To see five cases so far this year, it’s more than what we would expect."

Hawaii island had a total of four syphilis cases in the five-year period from 2008 through 2012 — two cases in 2009 and one each in 2011 and 2012.

The Health Department issued a medical advisory to physicians statewide Monday to raise awareness of a possible syphilis outbreak.

"Physicians don’t necessarily know what other physicians are seeing during the same time period," Hasty said.

Each of the five cases this year has affected men. Most of the cases involve men who have had sex with men, the department said. Health officials said they are concerned because there may be people who are infected and unaware of the illness who are traveling to other islands or abroad, risking a spread of the disease.

Hasty said the department is trying to find out the identities of the sexual partners in the current cases. "The only reason why we want to know is to make sure they get tested," he said. "If it goes untreated and unrecognized, it can be very severe."

Syphilis is a sexually transmitted disease passed from one person to another by a specific bacterium during unprotected sexual contact, according to a news release by the Health Department. The early stage of an infection is a painless ulcer that looks like a sore on the genitals, vagina or rectum. The sore could go away without treatment. Skin rashes also can occur and resolve without treatment.

Damage caused by syphilis could surface within a few years to a few decades from the initial infection. It can cause serious damage to the brain, nerves, eyes, heart, liver, bones and joints if not adequately treated. Infection also could increase a person’s chances of contracting HIV.

Health officials observed a spike in syphilis cases statewide from 2008 through 2010, numbering in the 20s and 30s those years compared to a typical number of 10 or fewer. He said it’s unclear what caused the increase to occur during that three-year period. It could be due to increased screening efforts, he said.

Sexual partners of an infected person are urged to get tested for syphilis even if they don’t see any signs of infection or illness.

For more information about possible syphilis infection, call your health care provider or the Department of Health’s STD/AIDS Prevention Branch at 733-9281 on Oahu, 821-2741 on Kauai, 984-2129 on Maui or 974-4247 on Hawaii island.