The number of dengue cases has gone up to 105,000 in Sri Lanka with 301 deaths, the Sri Lanka Red Cross Society said on Tuesday.

The Red Cross said it was rapidly scaling up emergency assistance to help contain one of the country’s worst-ever outbreak of dengue in recent times, reports Xinhua news agency.

The number of cases this year is already nearly double the number of dengue infections recorded in all of 2016 when 55,150 people were diagnosed with the disease.

“Dengue is endemic here but one reason for the dramatic rise in cases is that the virus currently spreading has evolved and people lack the immunity to fight off the new strain,” Novil Wijesekara from the Sri Lanka Red Cross said in a statement.

Compounding the crisis, monsoon rains and floods have left pools of stagnant water and rotting rain-soaked trash, which have been ideal breeding sites for mosquitoes.

Ongoing downpour and worsening sanitation conditions raise concerns the disease will continue to spread.