Page 115 - Invited Paper Session (IPS) - Volume 2

IPS186 Fagbamigbe, A. F.
sensitivity in the current study is comparable to the sensitivity of 89% but
lower than the specificity of 88% reported in an earlier longitudinal study in
Tanzania [8]. In the same report, 63% sensitivity and 94% specificity were
obtained in the cross-sectional component of the study. The authors noted
that these measurements of discriminatory analysis varied widely and it
depended on the presence of fever and the parasite density [8].
Murungi et al. noted that poor specificity in a diagnostic test may
negatively impact RDT-based diagnostic strategies for malaria [27]. The wide
disparities in the performance of RDTs against the microscopy and the PCR
motivated Murungi et al to explore the accuracy of the HRP2 and pLDH RDTs
and the microscopy in a two-step algorithm among 276 individuals. The
authors found varying and very high levels of sensitivity and specificity
depending on the stage of malaria. They concluded that certain RDTs could
be more accurate in new cases and initial diagnosis than in malaria case
monitoring and treatment and vice-versa [27].
On the predictive accuracy of the RDTs used in malaria diagnosis in the
current study, the PPV was low at 58% while the NPV was relatively high at
94% respectively. This finding suggests that the likelihood of having malaria
when the RDT test is positive is only about half while the likelihood of being
disease-free when the RDT test is negative is very high. In contrast, Hopkins et
al found that the PPV of the HRP2-based test was 98% compared with “the
expert” microscopy, with an NPV of 97% for the HRP2-based test [15]. Also, a
study carried out in Burkina Faso found the PPV and NPV of RDT to be 9% and
99.8% respectively in the dry season compared with 82% and 84% respectively
in the rainy season for infants to over 99% for adults [14]. However, it is worth
noting that PPVs are functions of disease prevalence.
Also, the level of anaemia influenced both the discriminatory and the
predictive accuracies of the RDTs. The RDTs were totally sensitive and less than
40% specific among children with severe anaemia. The higher the severity of
anaemia in children, the higher the sensitivity and the lower the specificity. In
a similar trend, PPV reduced with reducing anaemia severity while the NPV
increased with a reduction in the level of severity of anaemia.
Although, all the tests in the current study were carried out during the
same dry season which eliminated seasonal variability. It cannot be
ascertained in the current study if the dry season influenced the accuracies of
the RDTs in a study conducted in Burkina Faso. Bisofi et al. had found a
significant effect of seasonality in the discriminatory accuracy of RDT. It was
reported that while the sensitivity and specificity of the RDT were 86% and
90% respectively in the dry season, the figures were 94% and 78% respectively
in the rainy season [14]. The same study found seasonal variability in PPV and
NPV of RDT to be 9% and 99.8% respectively in the dry season compared with
82% and 84% respectively in the rainy season among infants [14]. In addition,

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