Comparison of field and expert laboratory microscopy for active surveillance for asymptomatic Plasmodium falciparum and Plasmodium vivax in western Thailand.

Abstract

Abstract. Microscopy of Giemsa-stained thick and thin films by a skilled microscopist has remained the standard laboratory method for the diagnosis of malaria. However, diagnosis of malaria with this method is problematic since interpretation of results requires considerable expertise, particularly at low parasite levels. We compared the efficacy of "field" and "expert laboratory" microscopy for active surveillance of Plasmodium falciparum and P. vivax in western Thailand. Field microscopy consisted of an approximately five-minute read (50−100 fields) of a thick film at ×700 using a natural light source, whereas expert laboratory microscopy consisted of a 20-minute read (number of parasites per 500 leukocytes) at ×1,000 using a high-quality, well-maintained microscope with an artificial light source. All discordant and 20% of concordant results were cross-checked blindly. A total of 3,004 blood films collected between May and November 2000 were included in the study, of which 156 (5.2%) were positive for P. falciparum, 177 (5.9%) for P. vivax, and 4 (0.1%) for both P. falciparum and P. vivax by expert microscopy. A total of 84.4% (135 of 160) of the P. falciparumpositive slides and 93.9% of the P. vivax-positive slides had a parasitemia of less than 500/L. Field microscopy was specific (99.3%) but not sensitive (10.0%) for the diagnosis of P. falciparum malaria, with a positive predictive value (PPV) of 43.2% and a negative predictive value (NPV) of 95.1%. The corresponding specificity and sensitivity for the diagnosis of P. vivax malaria were 99.2% and 7.1%, respectively, with a PPV of 38.7% and an NPV of 93.9%. Field microscopy, as defined in this study, is not an effective method for active malaria surveillance in western Thailand, where prevalence and parasitemia rates are low.

The Role of Laboratory Supervision in Improving the Quality of Malaria Diagnosis: A Pilot Study in Huambo, Angola

“…15 Although there is value in maintaining microscopic skills, the variability in technical capacity introduces a serious concern regarding diagnostic accuracy that has been reduced with the use of RDTs in other settings. [16][17][18][19] On the other hand, there are benefits of maintaining microscopy skills and not depending solely on RDTs. With microscopy, parasite density can be quantified.…”

Comparison of the Novel Partec Rapid Malaria Test to the Conventional Giemsa Stain and the Gold Standard Real-Time PCR

“…The reliable diagnosis of malaria requires laboratories at which rapid, sensitive, and specific tests are available at affordable cost. However, in many countries of malaria endemicity, laboratory techniques to confirm the clinical suspicion of malaria are considered to be too labor intensive (3) and unreliable, due to a lack of skilled microscopists, limited supplies, inadequate maintenance of microscopes and reagents, and inadequate or absent quality control systems (7). In general, the screening of Giemsa stains (GS) by light microscopy is still considered the gold standard (11).…”

“…This method is cheap and simple but labor intensive and time consuming and requires well-trained personnel (21), particularly for the detection of low levels of parasites (10). In resource-poor areas, microscopic diagnosis has been shown to be insensitive and nonspecific, especially when parasitemias are low or mixed infections are present (1,7). The sensitivity of thick-film microscopy is 10 to 30 parasites/l of blood (10).…”

Evaluation of three different DNA extraction methods from blood samples collected in dried filter paper in Plasmodium subpatent infections from the Amazon region in Brazil

“…In recent years asymptomatic Plasmodium infections have been reported in the Amazon region 2,15 . Although a thick smear is the gold standard for malaria diagnosis, this method is not efficient for diagnosing sub patent parasites in asymptomatic Plasmodium infections 5,14 . Molecular methods such as the Polymerase Chain Reaction (PCR) are efficient for increasing the sensitivity and specificity of Plasmodium diagnosis 3,13 especially in pauciparasitemics (individuals with few parasites detected in the blood) 13 .…”