What is the fine-grained topic of the following text: To confirm reports of a recent increase in transmission of stable malaria in the Oksibil Valley, which is at an elevation of 1,250–1,500 meters in the Jayawijaya Mountains of Irian Jaya, Indonesia, five malariometric surveys were conducted in four villages between May 1990 and July 1991. Only return the topic.
Investigation of increased malaria transmission in the Oksibil Valley, Indonesia