For this CP2 study the Faculty of Medicine, University of Colombo contributed samples from individuals in eight adjacent villages in Kataragama, a farming district in the dry lowland coastal plains of southeast Sri Lanka. Malaria transmission in the area is considered as "unstable" but endemic - it varies seasonally and is highest after the monsoon rainfalls in the winter (EIR 0-4 ib/p/year). Of special interest for CP2 is that in this setting, infections with Plasmodium vivax are more common than infections with Plasmodium falciparum, and that severe clinical symptoms are very rare.

The original study was a cohort study with active case detection of 1951 individuals  that were followed for 19 months during 1992/93. To obtain blood and DNA samples for CP2, 1133 of these individuals were traced again in 2006/7.

Description of Study Population

The sample population is almost entirely of Sinhala ethnic background (except for 7 Tamil individuals). Socio-demographic information on the entire population had been recorded since 1986.

Adults (>15) make up almost two thirds of the original (1992) study population (see summary on the right). At the time of plasma and DNA sampling, the entire population was older than 14 years

Morbidity and Infection Density

During the 1992 observation period, any infection with malaria parasites (Plasmodium vivax and falciparum) was recorded and parasite density determined relative to the number of red blood cells. About half of the infected individuals had only P.vivax infections, a quarter only P. falciparum. A self-reported history of malaria attacks since 1992 was asked in the 2006 observation period.

Clinical Information

Extensive clinical information was recorded for all 441 cases in this survey. A summary clinical score was then computed for 11 symptoms with a maximum score of 33. Temperature or haemoglobin levels were not included in this score and are not available for any given malaria attack, since only symptomatic infections were recorded.