Colombo, Aug 13 : Dengue fever has killed seven people so far this year in Sri Lanka, while the number of infected persons increased to 21,000, health officials here said. Most recently, over 300 confirmed dengue cases were reported and over 90 of them were in Colombo, Xinhua news agency reported citing the officials as saying on Thursday. They also said there was an increase in the mosquito population and warned of the risk of of dengue spreading further in the coming days, especially in urban and semi-urban areas. Preventing the spread of Dengue should be given special attention as there was an increased risk of the mosquito-borne disease with the prevailing monsoon rains, according to the officials. According to official data, April saw the highest number of dengue cases with 1,860 infections. Medical experts have urged the public to seek immediate medical service if they suffer high fever, uncontrolled vomiting, abdominal pain, or dizziness among other symptoms of dengue. /IANS