Puerto Rico's health secretary declared an epidemic on Monday following a spike in dengue cases.

The U.S. territory of 3.2 million people has reported at least 549 cases so far this year, compared with a total of 1,293 cases for all of last year. The majority of cases have been reported in the capital of San Juan.

More than 340 people have been hospitalized for the mosquito-borne virus, according to the island’s health department.

Puerto Rico last declared a dengue epidemic in 2012.

More than 5 million dengue cases were reported worldwide last year, with nearly 80% of them occurring in the Western Hemisphere, according the World Health Organization. The region has reported some 3 million cases so far this year, with health officials noting that higher rainfall along with humidity and heat linked to climate change have contributed to a rise in cases.

The virus can cause crushing headaches, fever, vomiting, a rash and other symptoms. While most infected people don’t get symptoms, severe cases can lead to plasma leakage and death.