From a total of 535 blood samples collected from Chinese migrants, 162 (30.28%) tested positive for malaria infections, of which 99 (61.11%) were positive for P. falciparum, three (1.85%) were positive for P. vivax, five (3.09%) for P. malariae, 50 (30.86%) for P. ovale, while five had mixed infections. The median, maximum, and minimum age of the study participants were 40.87, 64 and 18, respectively. More than 98.32% of the study participants were male. The microscopy and PCR malaria positivity rates, used as the reference standards, were 30.28%, while the malaria positivity rates using the novel RDT and the commercial RDT were 22.43% and 25.98%, respectively. The PCR malaria positivity rate, used as a reference standard, was 30.28%.
Visual comparison of the results of the novel and commercial RDT in the Plasmodium blood sample test
The novel malaria RDT could differentiate P. falciparum (colour in T1) and P. vivax (colour in T2, no colour in T1). A positive test for P. malariae or P. ovale infection was indicated by colour in T3 (no colour in T1 and T2). However, it was challenging distinguishing between P. ovale and P. malariae infections. The commercial RDT test could differentiate P. falciparum (T1 displaying colour) from other Plasmodium species (P. vivax, P. malariae, or P.ovale). The presence of these three Plasmodium was indicated by colour in T3 (no colour in T1 and T2). However, this test could not distinguish between these three species. (Fig. 1)
The detection of different Plasmodium species using the two RDTs
Using the microscopy and PCR results as the reference standards (a case was regarded positive when either test result was positive), the novel malaria RDT had a total sensitivity of 74.1%, specificity of 93.0%, and test efficiency of 87.3%, Kappa = 0.690 (P < 0.0001). The sensitivity of detecting P. falciparum, P. vivax, P. malariae, and P. ovale was 91.9%, 100%, 20.0%, and 44.0%, respectively. The commercial RDT had a total sensitivity of 86.0%, specificity of 89.3%, and test efficiency of 88.2%, Kappa = 0.729 (P < 0.0001). The sensitivity of detecting P. falciparum, P. vivax, P. malariae, and P. ovale was 96.0%, 100%, 40.0%, and 70.0%, respectively ( Tables 2 and 3).
Table 2
Test results of the two RDTs in imported cases
Microscopy results | Number of cases | Number of positive cases |
Commercial RDT | | Novel malaria RDT |
Pf | Pan | | Pf | Pv | Pan |
Pf | 99 | 95 | / | | 91 | / | / |
Pv | 3 | 0 | 3 | | 0 | 3 | / |
Pm | 5 | 0 | 2 | | 0 | 0 | 1 |
Po | 50 | 0 | 35 | | 0 | 0 | 22 |
Mix | 5 | 2 | 2 | | 2 | 1 | 0 |
Total | 162 | 139 | | 120 |
(-) | 373 | 40 | | 26 |
(Among the five mix infection cases, two were Po and Pf, one was Po and Pv, and two were Po and Pm). Pf, P. falciparum; Pv, P. vivax,; Pm, P. malariae; Po, P.ovale.
Table 3
Diagnostic performance of the novel and commercial RDTs in the detection of malaria
Diagnostic parameter | Total | | Pf | | Pv | | Pm | | Po |
Commercial | Novel | | Commercial | Novel | | Commercial | Novel | | Commercial | Novel | | Commercial | Novel |
True positive | 139 | 120 | | 95 | 91 | | 3 | 3 | | 2 | 1 | | 35 | 22 |
True negative | 333 | 347 | | 333 | 347 | | 333 | 347 | | 333 | 347 | | 333 | 347 |
False positive | 40 | 26 | | 40 | 26 | | 40 | 26 | | 40 | 26 | | 40 | 26 |
False negative | 23 | 42 | | 4 | 8 | | 0 | 0 | | 3 | 4 | | 15 | 28 |
Sensitivity (%) (95% CI) | 85.8 | 74.1 | | 96.0 | 91.9 | | 100 | 100 | | 40.0 | 20.0 | | 70.0 | 44.0 |
79.25–90.60 | 66.49–80.49 | | 89.39–98.70 | 84.24–96.19 | | 31.00-100 | 31.00-100 | | 7.26–82.96 | 1.05–70.12 | | 55.22–81.71 | 30.27–58.65 |
Specificity (%) (95% CI) | 89.3 | 93.0 | | 89.3 | 93.0 | | 89.3 | 93.0 | | 89.3 | 93.0 | | 89.3 | 93.0 |
85.58–92.14 | 89.83–95.31 | | 85.58–92.14 | 89.83–95.31 | | 85.58–92.14 | 89.83–95.31 | | 85.58–92.14 | 89.83–95.31 | | 85.58–92.14 | 89.83–95.31 |
Diagnostic efficiency (%) | 88.2 | 87.3 | | 90.7 | 92.8 | | 89.4 | 93.1 | | 88.6 | 92.1 | | 87.0 | 87.2 |
Differential analysis of P. falciparum and other Plasmodium species
The commercial RDT had a specificity of 89.3%, with a P. falciparum-detection sensitivity of 96.0% (Kappa = 0.752; P < 0.0001), while its detection sensitivity for other Plasmodium species was 69.0% (Kappa = 0.502; P < 0.0001). The novel malaria RDT had a specificity of 93.0%, with a P. falciparum-detection sensitivity of 91.9% (Kappa = 0.796;P < 0.0001) and a detection sensitivity of 44.8% for other Plasmodium species (Kappa = 0.396; P < 0.0001) (Table 4).
Table 4
Comparison of test results between P. falciparum and other species
Microscopy results | Sample number | Commercial RDT | | Novel malaria RDT |
Positive | Negative | Detection rate (%) | | Positive | Negative | Detection rate (%) |
Pf | 99 | 95 | 4 | 96.0 | | 91 | 8 | 91.9 |
Other Plasmodium species | 58 | 40 | 18 | 69.0 | | 26 | 32 | 44.8 |
Mix. | 5 | 4 | 1 | 80.0 | | 3 | 2 | 60.0 |
(-) | 373 | 40 | 333 | 10.7 | | 26 | 347 | 7.0 |
A differential visual comparison between the commercial and novel malaria RDTs showed a statistically significant difference (χ2 = 14.73; P = 0.0001) in the P. falciparum detection rate, with a good consistency according to Kappa analysis. Furthermore, a statistically significant difference (χ2 = 24.50; P < 0.0001) regarding the detection rate of other Plasmodium species was observed with Kappa analysis-based average consistency (Kappa = 0.716).