Data and study characteristics
The literature search generated 466 results in PubMed, 354 in Scopus, 271 in Web of Science and 909 in Elsevier (Fig. 1). After removing duplicates, 1202 articles were left for screening. Following screening of titles and abstracts, 295 studies were retained for more detailed evaluation. The most common reason for exclusion was the unavailability of data for analysis. Other reasons for exclusion including experimental studies, cohort studies, and reviews. As a result, 46 articles were selected in the study for full data extraction (5, 7–9, 21–23, 25, 26, 29–65).
Description Of Included Studies
Of the 46 included studies, six studies (13%) were published from 1988 to 1999, followed by 11 studies (24%) from 2000 to 2010 and 29 studies (63%) from 2011 to June 2019 (Table 1). Majority of studies were conducted in Malaysia Borneo (31/46; 67.4%), followed by Peninsular Malaysia (13/46; 28.3%) and in both areas (2/46; 4.3%). In term of sampling strategy, 33 studies derived from hospital data, 12 studies from population data and only one study from the combination of both hospital and population data.
Table 1
Summary of main features of included articles.
No. | References | Sample size (N) | Period of sample collection1 | Study area2 | Prevalence by microscopy, n (%) | Pf, Pv, Pm, Po by microscopy; n (%) | Pk by microscopy; n (%) | Mixed infection by microscopy; n (%) | Prevalence by PCR, n (%) | Pf, Pv, Pm, Po by PCR; n (%) | Pk by PCR; n (%) | Mixed infection by PCR; n (%) |
1 | Jiram AI et al. 2019 | 1995 | 2013–2014 | Borneo | 0 (0.0) | 0 (0.0) | 0 | 0 (0.0) | 145 (7.3) | 116 (80) | 9 (6.2) | 20 (13.8) |
2 | Cooper DJ et al 20193 | 3867 | 2015–2017 | Borneo | 3788 (98.0) | 264 (7.0) | 3524 (93.0) | 0 (0.0) | 3580 (99.5) | 283 (7.9) | 3262 (91.1) | |
3 | Grigg MJ et al. 2018 | 852 | 2012–2016 | Borneo | 846 (99.3) | 81 (9.6) | | 7 (0.8) | | | | |
4 | Grigg MJ et al. 20183 | 872 | 2012–2016 | Borneo | 854 (97.9) | 309 (36.2) | 529 (61.9) | | 789 (97.3) | 300 (38.0) | 482 (61.1) | 6 (0.8) |
5 | Jeffree SM et al. 2018 | 470 | 2012 | Borneo | 11 (2.3) | 11 (100.0) | 0 (0.0) | 0 (0.0) | | 0 | | |
6 | Liew JWK et al. 2018 | 3757 | 2016–2017 | Peninsular | 164 (4.4) | 164 (100.0) | 0 (0.0) | 0 (0.0) | 43 (26.5) | 43 (100.0) | | |
7 | Siner A et al. 2017 | 3002 | 2014–2015 | Borneo | 5 (0.2) | 0 (0.0) | 5 (100.0) | 0 (0.0) | 9 (0.3) | 1 (11.1) | 7 (77.8) | |
8 | Grigg MJ et al. 20173 | 414 | 2012–2015 | Borneo | 414 (100) | | | | 412 (99.5) | 90 (21.8) | 268 (65.0) | 2 (0.5) |
9 | Mohd Abdul Razak MR et al. 20163 | 4257 | 2008–2009, 2011, 2014 | Borneo | 112 (2.6) | 60 (53.6) | | | 112 (2.6) | | | |
10 | Britton S et al. 20163 | 261 | 2012 | Borneo | 149 (57.1) | | | | 149 (57.1) | 88 (59.1) | 56 (37.6) | 1 (0.7) |
11 | Stanis CS et al. 20163 | 129 | 2012–2013 | Borneo | 109 (84.5) | 101 (92.7) | 6 (5.5) | 2 (1.8) | 103 (79.8) | 35 (34.0) | 68 (66.0) | |
12 | Fornace KM et al 20163 | 2006 | 2008–2012 | Borneo | 1847 (100) | 1847 (1847) | 0 (0.0) | 0 (0.0) | 346 (100.0) | 33 (9.5) | 313 (90.5) | |
13 | Jiram AI et al. 2016 | 306 | | Peninsular | | | | | 113 (36.9) | 59 (52.2) | 23 (20.4) | 31 (52.5) |
14 | Othman N et al 20153 | 94 | 2007–2010 | Borneo | 94 (100) | 93 (98.9) | 0 (0.0) | 1 (1.1) | 94 (100) | 92 (98.9) | | 2 (2.1) |
15 | Fornace KM et al 2015 | 1147 | 2012–2014 | Borneo | 1 (0.1) | | | | 206 (18.0) | | 20 (9.7) | |
16 | Lee PC et al 2015 | 207 | 2012–2013 | Borneo | | | | | 207 (100) | 53 (25.7) | 152 (73.4) | |
17 | Chua KH et al. 2015 | 229 | 2008–2010 | Borneo | 215 (93.9) | 214 (99.5) | 0 (0.0) | 1 (0.5) | 226 (98.7) | 185 (89.4) | 36 (15.9) | 2 (0.9) |
18 | Barber BE et al. 2015 | 774 | 2012–2013 | Borneo | 774 (100) | 757 (97.8) | 0 (0.0) | 17 (2.2) | | | | |
19 | Vythilingam I et al. 2014 | 4353 | 2009–2013 | Peninsular | 1284 (29.5) | 1262 (98.3) | 0 (0.0) | 22 (1.7) | | | | |
20 | Foster D et al. 2014 | 84 | 2010–2011 | Borneo | | | | | 84 (100.0) | 15 (17.9) | 69 (82.1) | |
21 | Yusof R et al. 20143 | 457 | | Borneo and Peninsular | 457 (100) | 274 (60.0) | 181 (39.6) | 2 (0.4) | 453 (99.1) | 185 (40.8) | 256 (56.5) | 12 (2.6) |
22 | Braima et al 2013 | 1623 | 2006–2012 | Peninsular | 1623 (100) | 1522 (93.8) | 75 (4.6) | 26 (1.6) | | | | |
23 | Goh XT et al. 20133 | 189 | 2008–2011 | Borneo | 189 (100) | 186 (98.4) | 0 (0.0) | 3 (1.6) | 178 (94.2) | 134 (75.3) | 42 (24.0) | 2 (1.1) |
24 | Barber BE et al. 20133 | 387 | 2010–2011 | Borneo | 387 (100) | 221 (57.1) | 150 (38.8) | 16 (4.1) | 295 (100.0) | 165 (55.9) | 130 (44.1) | |
25 | Barber BE et al. 20123 | 18993 | 2009–2011 | Borneo | 653 (3.4) | 558 (85.5) | 0 (0.0) | 95 (14.5) | 475 (97.9) | 58 (12.2) | 345 (72.3) | 48 (10.1) |
26 | Khin D et al. 20113 | 445 | 2009 | Borneo | 445 (100) | 318 (71.5) | 0 (0.0) | 25 (5.6) | 343 (100.0) | | 256 (74.6 ) | 87 (25.4) |
27 | Norahmad NA et al. 2011 | 619 | 2008–2009 | Borneo | 58 (9.4) | 31 (53.4) | | | | | | |
28 | William T et al. 20113 | 78 | 2007–2009 | Borneo | 78 (100) | 0 (0.0) | 0 (0.0) | 0 (0.0) | 63 (100.0) | 2 (3.2) | 56 (88.9) | 5 (7.9) |
29 | Barber BE et al 20113 | 220 | 2009 | Borneo | 220 (100) | 184 (83.6) | 0 (0.0) | 36 (16.4) | 155 (96.3) | 9 (5.8) | 127 (81.9) | 12 (7.7) |
30 | Daneshvar C et al. 2009 | 188 | 2006–2008 | Borneo | 188 (100) | 60 (31.9) | 121 (64.4) | 7 (3.7) | | | | |
31 | Lee KS et al. 20093 | 47 | 1996 | Borneo | 47 (100) | 47 (100.0) | 0 (0.0) | 0 (0.0) | 36 (76.6) | 1 (2.8) | 29 (80.6) | 6 (16.7) |
32 | Kaur Gurpreet 2009 | 520 | 2000–2001 | Peninsular | 126 (24.2) | 126 (100.0) | 0 (0.0) | 0 (0.0) | | | | |
33 | Vythilingam I et al. 20083 | 111 | 2005–2008 | Borneo and Peninsular | 111 (100) | 108 (97.3) | 0 (0.0) | 3 (2.7) | 111 (100.0) | 33 (29.7) | 65 (58.6) | 13 (11.7) |
34 | Cox-Singh J et al. 20083 | 960 | 2001–2006 | Borneo | 960 (100) | 958 (99.8) | 0 (0.0) | 2 (0.2) | 960 (100.0) | 664 (69.2) | 243 (25.3) | 53 (5.5) |
35 | Nimir AR et al. 2006 | 382 | 1998–2003 | Peninsular | 382 (100) | 347 (90.8) | 0 (0.0) | 35 (9.2) | | | | |
36 | Jamaiah I et al. 2006 | 94 | 1999–2004 | Peninsular | 94 (100) | 89 (94.7) | 0 (0.0) | 5 (5.3) | | | | |
37 | Jamaiah I et al. 2005 | 86 | 1994–2003 | Peninsular | 86 (100) | 76 (88.4) | 0 (0.0) | 8 (9.3) | | | | |
38 | Singh B et al. 20043 | 208 | 2000–2002 | Borneo | 208 (100) | 208 (100.0) | 0 (0.0) | 0 (0.0) | 208 (100.0) | 82 (39.4) | 106 (51.0) | 20 (9.6) |
39 | Koh KH et al. 2004 | 31 | 1996–2001 | Borneo | 31 (100) | 30 (96.8) | 0 (0.0) | 1 (3.2) | | | | |
40 | Norhayati M et al. 2001 | 310 | | Peninsular | 34 (11) | 34 (100.0) | 0 (0.0) | 0 (0.0) | | | | |
41 | Singh B et al. 1999 | 129 | | Borneo | 36 (27.9) | 31 (86.1) | 0 (0.0) | 5 (13.9) | 43 (33.3) | 32 (74.4) | 0 (0.0) | 11 (25.6) |
42 | Jamaiah I et al. 1998 | 134 | 1983–1992 | Peninsular | 134 (100) | 123 (91.8) | 0 (0.0) | 11 (8.2) | | | | |
43 | Singh B et al. 1996 | 166 | | Borneo | 68 (41) | 62 (91.2) | 0 (0.0) | 6 (8.8) | 73 (44.0) | 65 (89.0) | 0 (0.0) | 8 (11.0) |
44 | Sidhu PS et al 1991 | 64 | 1984–1988 | Peninsular | 64 (100) | 62 (96.9) | 0 (0.0) | 2 (3.1) | | | | |
45 | Gordon DM et al. 1991 | 268 | | Peninsular | 60 (22.4) | 50 (83.3) | 0 (0.0) | 10 (16.7) | | | | |
46 | Lee M et al. 1988 | 94 | 1986 | Peninsular | 45 (47.9) | 23 (51.1) | 0 (0.0) | 22 (48.9) | | | | |
1Total of six studies has no data on period of sample collection. Some studies do not explicitly stratify the number of cases in each year. |
2 Borneo including the states of Sabah and Sarawak in East Malaysia |
3Studies with PCR diagnosis derived from a subset of microscopy positive data Pf = P. falciparum; Pv = P. vivax; Pm = P. malariae; Po = P. ovale and Pk = P. knowlesi |
In term of malaria diagnosis method, 28 studies utilised both microscopy and PCR but in 18 of them, the samples tested for PCR were chosen from the microscopy positive cases for malaria species confirmation. Of those 18 studies tested for PCR, ten studies (7–9, 33–35, 38, 51, 53, 57) used all the microscopy positive cases, six studies (5, 30, 44, 46, 48, 49) used more than 70% of the cases, one study (45) used for 2.5% randomly selected cases, and one study (36) used for 19% of microscopy positive cases for either two Plasmodium spp. namely P. malariae or P. knowlesi. Furthermore, of the 28 studies, ten studies (12, 22, 23, 26, 29, 32, 39, 50, 59, 61) conducted PCR in the whole samples regardless of the microscopy results in order to trace the sub-microscopic infections. In addition, 18 studies utilised only one method of detection for malaria. Among them, 15 studies (31, 40, 41, 43, 47, 52, 54–56, 58, 60, 62–65) and three studies (25, 37, 42) were using microscopy and PCR, respectively.
In overall, the median sample size for cases were 308 (range 31-18993) for microscopy and 261 (range 47-4257) for PCR. Most microscopy measurements used Giemsa-stained thick and thin smears (n = 38), while the remaining studies (n = 8) used only thick smear. In term of PCR method, majority of studies used conventional nested PCR (n = 22), followed by three studies used multiplex PCR and two studies used real-time PCR. Other studies (n = 4) reported combination of different PCR methods; conventional/multiplex/real-time PCR, loop-mediated isothermal amplification (LAMP) assays (35), conventional/multiplex PCR assays (26), conventional/real-time PCR assays (12), and multiplex/real-time PCR assays (25).
Trend Of Malaria Cases By Species
The cumulative number and trend of confirmed malaria species by year of sampling is show in Fig. 2. Based on the year of sampling, detection of Plasmodium species by microscopy were highest in 2012 (43) for P. vivax, P. malariae/P. knowlesi and P. falciparum. Whereas, highest number of P. knowlesi cases was reported in 2016 with 529 cases (30) and only one (9, 39, 41, 43) and two (50, 53) cases of P. ovale were reported. Except for P. knowlesi, there was a declining trend of all human malaria species throughout the study period. Similarly, the identification of Plasmodium species by PCR revealed that P. knowlesi cases rose steadily throughout the year and peaked in 2017 (5). The trend of human malaria cases by PCR was low with less than 30 cases reported in 2017 and no mixed infection reported.
Prevalence Measurements
The prevalence of malaria cases measured by PCR was consistently higher than the prevalence measured by microscopy (Fig. 3). The mean prevalence by PCR and microscopy were 48.5% (95% confidence interval [CI]: 47.8–49.1) and 31.2% (95% CI: 30.8–31.6), respectively. Across the studies, prevalent by microscopy correlated significantly with prevalent by PCR (Correlation of determination, R2: 0.7782, P < 0.0001).
Sensitivity And Specificity Of Detection Methods
The performance of microscopy and PCR in detecting Plasmodium spp. are shown in Fig. 4. In total, 21 studies were included; 18 studies were undertaken in Malaysia Borneo (5, 7, 22, 23, 26, 30, 36, 38, 39, 44–46, 49, 51, 53, 57, 59, 61), one study was in Peninsular Malaysia (32) and two studies were in both Peninsular Malaysia and Malaysia Borneo (8, 9). Overall, the summary estimate of sensitivity by microscopy was highest for P. knowlesi (35% [95% CI: 34–36]), followed by P. malariae (25% [95% CI: 24–26]) and P. vivax (14% [95% CI: 14–15]), and lowest for P. falciparum (11% [95% CI: 10–11]). Nevertheless, the summary estimate of specificity by microscopy was similar in all species ranged 40% − 43%.
Similar to microscopy, the summary estimate of sensitivity by PCR was highest for P. knowlesi with 56% (95% CI: 55–57). Whereas, the summary estimate of sensitivity by PCR for P. vivax, P. falciparum and P. malariae were 14% (95% CI: 13–15), 11% (95% CI: 10–11) and 1.6% (95% CI: 1.4–1.9), respectively. On the other hand, the specificities of summary estimate for species-specific were less than 35% with P. knowlesi, P. vivax, P. falciparum and P. malariae were 34.5% (95% CI: 34–35), 34% (95% CI: 33–35), 16.5% (95% CI: 16–17) and 2.3% (95% CI: 2–3), respectively.