Comparison of PCR and microscopy for the detection of asymptomatic malaria in a Plasmodium falciparum/vivax endemic area in Thailand.
OBJECTIVE
The main objective of this study was to compare the performance of nested PCR with expert microscopy as a means of detecting Plasmodium parasites during active malaria surveillance in western Thailand.


METHODS
The study was performed from May 2000 to April 2002 in the village of Kong Mong Tha, located in western Thailand. Plasmodium vivax (PV) and Plasmodium falciparum (PF) are the predominant parasite species in this village, followed by Plasmodium malariae (PM) and Plasmodium ovale (PO). Each month, fingerprick blood samples were taken from each participating individual and used to prepare thick and thin blood films and for PCR analysis.


RESULTS
PCR was sensitive (96%) and specific (98%) for malaria at parasite densities > or = 500/microl; however, only 18% (47/269) of P. falciparum- and 5% (20/390) of P. vivax-positive films had parasite densities this high. Performance of PCR decreased markedly at parasite densities <500/microl, with sensitivity of only 20% for P. falciparum and 24% for P. vivax at densities <100 parasites/microl.


CONCLUSIONS
Although PCR performance appeared poor when compared to microscopy, data indicated that the discrepancy between the two methods resulted from poor performance of microscopy at low parasite densities rather than poor performance of PCR. These data are not unusual when the diagnostic method being evaluated is more sensitive than the reference method. PCR appears to be a useful method for detecting Plasmodium parasites during active malaria surveillance in Thailand.
Coleman
Russell E
RE
Departments of Entomology and Immunology, US Army Medical Component, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand. russell.coleman@na.amedd.army.mil
Sattabongkot
Jetsumon
J
Promstaporm
Sommai
S
Maneechai
Nongnuj
N
Tippayachai
Bousaraporn
B
Kengluecha
Ampornpan
A
Rachapaew
Nattawan
N
Zollner
Gabriela
G
Miller
Robert Scott
RS
Vaughan
Jefferson A
JA
Thimasarn
Krongtong
K
Khuntirat
Benjawan
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D016778:Malaria, Falciparum / Q000175:diagnosis* / Q000469:parasitology; D016780:Malaria, Vivax / Q000175:diagnosis* / Q000469:parasitology; D008297:Male; D008859:Microscopy, Polarization / Q000379:methods*; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000235:genetics / Q000302:isolation & purification*; D010966:Plasmodium vivax / Q000235:genetics / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D013785:Thailand