Validity of Lot Quality Assurance Sampling to optimize falciparum malaria surveys in low-transmission areas

To control the reappearance of malaria in the Madagascan highlands, indoor house-spraying of DDT was conducted from 1993 until 1998. Before the end of the insecticide-spraying programme, a surveillance system was set up to al low rapid identification of new malaria epidemics. When the number of suspe cted clinical malaria cases notified to the surveillance system exceeds a p redetermined threshold, a parasitological survey is carried out in the comm unity to confirm whether or nut transmission of falciparum malaria is incre asing. Owing to the low specificity of the surveillance system, this confir mation stage is essential to guide the activities of the control programme. For this purpose, Lot Quality Assurance Sampling (LQAS), which usually req uires smaller sample sizes, seemed to be a valuable alternative to conventi onal survey methods. In parallel to a conventional study of Plasmodium falc iparum prevalence carried out in 1998, we investigated the ability of LQAS to rapidly classify zones according to a predetermined prevalence level. Tw o prevalence thresholds (5% and 15%) were tested using various sampling pla ns. A plan (36, 2), meaning that at least 2 individuals found to be positiv e among a random sample of 36, enabled us to classify a community correctly with a sensitivity of 100% and a specificity of 94%. LQAS is an effective tool for rapid assessment of falciparum malaria prevalence when monitoring malaria transmission.