The performance and utility of rapid diagnostic assays for Plasmodium falciparum malaria in a field setting in the Lao People's Democratic Republic.

Rapid diagnostic assays for malaria have the potential to improve the management and control of the disease in developing countries. The objectives of the present study were to evaluate, in a field setting, the performance of several such assays for Plasmodium falciparum infection and to examine the usefulness of these assays in identifying subjects for treatment trials in rural field sites. Residents of 12 villages in Laos who presented with fever were eligible for inclusion. Blood was collected by fingerprick for a dipstick assay, developed by the Program for Appropriate Technology in Health (PATH), performed and interpreted in the field by local healthcare workers. Compared with 'blinded' reference microscopy (N =196), the sensitivity and specificity of the PATH assay were 96.2% and 93.0%, respectively. Two rapid diagnostic assays (PATH and OptiMAL) were also performed on the subset of subjects eligible to participate in an in-vivo treatment trial (N = 97), and the results again compared with those of 'blinded' reference microscopy. In this subset, a subject was considered a 'true positive' if found positive by microscopy or the alternate rapid assay. Using this modified reference standard, the sensitivity and specificity of the PATH assay were 96.7% and 94.4%, and those of the OptiMAL assay were 91.8% and 100%, respectively. Both of the rapid assays tested therefore appear suitable for use in rural field settings by local healthcare providers and can accurately identify participants for treatment trials.

Plasmodium falciparum malaria in Laos: chloroquine treatment outcome and predictive value of molecular markers.

A 28-day treatment trial was undertaken, to determine the efficacy of chloroquine in Laos and to assess the predictive value of molecular markers (cg2, pfmdr1, and pfcrt) that were previously linked to chloroquine resistance. In total, 522 febrile patients were screened for falciparum malaria by rapid diagnostic assays. Of 81 patients (15.5% prevalence) who were positive by the assays and microscopy, 48 were eligible to participate in the 28-day trial. Nine patients defaulted. Chloroquine cured 54% (95% confidence interval, 45.8-61.8) of falciparum-infected patients. Of 18 (46%) patients with treatment failure, 13 (72%) experienced high-grade resistance. Polymorphisms in cg2 and the N86Y mutation in PfMDR1 were not predictive of treatment outcome. A mutation in PfCRT (K76T) was perfectly associated with in vivo chloroquine resistance. However, K76T was also present in in vivo-sensitive isolates, which suggests that the presence of this mutation was necessary, but not sufficient, to predict in vivo outcome in this cohort.