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Comparison of real-time PCR and microscopy for malaria parasite detection in Malawian pregnant women.

Rantala AM, Taylor SM, Trottman PA, Luntamo M, Mbewe B, Maleta K, Kulmala T, Ashorn P, Meshnick SR - Malar. J. (2010)

Bottom Line: These molecular methods will enable further studies on the effects of these submicroscopic infections on maternal health and birth outcomes.If a Ct value of 38 was used as a cut-off, specificity improved to 94.6% with no change in sensitivity.Determination of the possible contribution of these submicroscopic infections to poor birth outcomes and maternal health is critical.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of International Health, University of Tampere Medical School, Tampere, Finland.

ABSTRACT

Background: New diagnostic tools for malaria are required owing to the changing epidemiology of malaria, particularly among pregnant women in sub-Saharan Africa. Real-time PCR assays targeting Plasmodium falciparum lactate dehydrogenase (pfldh) gene may facilitate the identification of a high proportion of pregnant women with a P. falciparum parasitaemia below the threshold of microscopy. These molecular methods will enable further studies on the effects of these submicroscopic infections on maternal health and birth outcomes.

Methods: The pfldh real-time PCR assay and conventional microscopy were compared for the detection of P. falciparum from dried blood spots and blood smears collected from the peripheral blood of 475 Malawian women at delivery. A cycle threshold (Ct) of the real-time PCR was determined optimizing the sensitivity and specificity of the pfldh PCR assay compared to microscopy. A real-time PCR species-specific assay was applied to identify the contribution to malaria infections of three Plasmodium species (P. falciparum P. ovale and P. malariae) in 44 discordant smear and pfldh PCR assay results.

Results: Of the 475 women, P. falciparum was detected in 11 (2.3%) by microscopy and in 51 (10.7%) by real-time PCR; compared to microscopy, the sensitivity of real-time PCR was 90.9% and the specificity 91.2%. If a Ct value of 38 was used as a cut-off, specificity improved to 94.6% with no change in sensitivity. The real-time PCR species-specific assay detected P. falciparum alone in all but four samples: two samples were mixed infections with P. falciparum and P. malariae, one was a pure P. malariae infection and one was a pfldh PCR assay-positive/species-specific assay-negative sample. Of three P. malariae infections detected by microscopy, only one was confirmed by the species-specific assay.

Conclusions: Although microscopy remains the most appropriate method for clinical malaria diagnosis in field settings, molecular diagnostics such as real-time PCR offer a more reliable means to detect malaria parasites, particularly at low levels. Determination of the possible contribution of these submicroscopic infections to poor birth outcomes and maternal health is critical. For future studies to investigate these effects, this pfldh real-time PCR assay offers a reliable detection method.

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Comparison of P. falciparum infections detected by microscopy and the pfldh real-time PCR assay at delivery by calendar months.
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Figure 1: Comparison of P. falciparum infections detected by microscopy and the pfldh real-time PCR assay at delivery by calendar months.

Mentions: Of 475 women at delivery, P. falciparum was detected in 11 (2.3%) by microscopy. Three additional patients had P. malariae monoinfections detected microscopically. In contrast, 51 (10.7%) samples were positive for P. falciparum by the pfldh PCR assay (Table 3). Of the 11 samples found to have P. falciparum by microscopy, 10 were positive in the pfldh PCR assay. Of the 464 microscopy-negative samples, 41 were positive in the pfldh PCR assay. Compared to microscopy, the sensitivity of real-time PCR for detection of P. falciparum was 90.9% and the specificity 91.2%. Submicroscopic infections were most prevalent during and after the rainy season in January-April, while microscopic malaria prevalence peaked only at the earlier part of the rainy season (January and February) (Figure 1). Thus, for example, there were 9 cases of P. falciparum by pfldh PCR, vs 1 by microscopy in April, while in July PCR and microscopy detected the same number of infections (one each).


Comparison of real-time PCR and microscopy for malaria parasite detection in Malawian pregnant women.

Rantala AM, Taylor SM, Trottman PA, Luntamo M, Mbewe B, Maleta K, Kulmala T, Ashorn P, Meshnick SR - Malar. J. (2010)

Comparison of P. falciparum infections detected by microscopy and the pfldh real-time PCR assay at delivery by calendar months.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2984567&req=5

Figure 1: Comparison of P. falciparum infections detected by microscopy and the pfldh real-time PCR assay at delivery by calendar months.
Mentions: Of 475 women at delivery, P. falciparum was detected in 11 (2.3%) by microscopy. Three additional patients had P. malariae monoinfections detected microscopically. In contrast, 51 (10.7%) samples were positive for P. falciparum by the pfldh PCR assay (Table 3). Of the 11 samples found to have P. falciparum by microscopy, 10 were positive in the pfldh PCR assay. Of the 464 microscopy-negative samples, 41 were positive in the pfldh PCR assay. Compared to microscopy, the sensitivity of real-time PCR for detection of P. falciparum was 90.9% and the specificity 91.2%. Submicroscopic infections were most prevalent during and after the rainy season in January-April, while microscopic malaria prevalence peaked only at the earlier part of the rainy season (January and February) (Figure 1). Thus, for example, there were 9 cases of P. falciparum by pfldh PCR, vs 1 by microscopy in April, while in July PCR and microscopy detected the same number of infections (one each).

Bottom Line: These molecular methods will enable further studies on the effects of these submicroscopic infections on maternal health and birth outcomes.If a Ct value of 38 was used as a cut-off, specificity improved to 94.6% with no change in sensitivity.Determination of the possible contribution of these submicroscopic infections to poor birth outcomes and maternal health is critical.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of International Health, University of Tampere Medical School, Tampere, Finland.

ABSTRACT

Background: New diagnostic tools for malaria are required owing to the changing epidemiology of malaria, particularly among pregnant women in sub-Saharan Africa. Real-time PCR assays targeting Plasmodium falciparum lactate dehydrogenase (pfldh) gene may facilitate the identification of a high proportion of pregnant women with a P. falciparum parasitaemia below the threshold of microscopy. These molecular methods will enable further studies on the effects of these submicroscopic infections on maternal health and birth outcomes.

Methods: The pfldh real-time PCR assay and conventional microscopy were compared for the detection of P. falciparum from dried blood spots and blood smears collected from the peripheral blood of 475 Malawian women at delivery. A cycle threshold (Ct) of the real-time PCR was determined optimizing the sensitivity and specificity of the pfldh PCR assay compared to microscopy. A real-time PCR species-specific assay was applied to identify the contribution to malaria infections of three Plasmodium species (P. falciparum P. ovale and P. malariae) in 44 discordant smear and pfldh PCR assay results.

Results: Of the 475 women, P. falciparum was detected in 11 (2.3%) by microscopy and in 51 (10.7%) by real-time PCR; compared to microscopy, the sensitivity of real-time PCR was 90.9% and the specificity 91.2%. If a Ct value of 38 was used as a cut-off, specificity improved to 94.6% with no change in sensitivity. The real-time PCR species-specific assay detected P. falciparum alone in all but four samples: two samples were mixed infections with P. falciparum and P. malariae, one was a pure P. malariae infection and one was a pfldh PCR assay-positive/species-specific assay-negative sample. Of three P. malariae infections detected by microscopy, only one was confirmed by the species-specific assay.

Conclusions: Although microscopy remains the most appropriate method for clinical malaria diagnosis in field settings, molecular diagnostics such as real-time PCR offer a more reliable means to detect malaria parasites, particularly at low levels. Determination of the possible contribution of these submicroscopic infections to poor birth outcomes and maternal health is critical. For future studies to investigate these effects, this pfldh real-time PCR assay offers a reliable detection method.

Show MeSH
Related in: MedlinePlus