Comparison of diagnostics for the detection of asymptomatic Plasmodium falciparum infections to inform control and elimination strategies

Abstract

The global burden of malaria has been substantially reduced over the past two decades. Future efforts to reduce malaria further will require moving beyond the treatment of clinical infections to targeting malaria transmission more broadly in the community. As such, the accurate identification of asymptomatic human infections, which can sustain a large proportion of transmission, is becoming a vital component of control and elimination programmes. We determined the relationship across common diagnostics used to measure malaria prevalence -polymerase chain reaction (PCR), rapid diagnostic test and microscopy -for the detection of Plasmodium falciparum infections in endemic populations based on a pooled analysis of cross-sectional data. We included data from more than 170,000 individuals comparing the detection by rapid diagnostic test and microscopy, and 30,000 for detection by rapid diagnostic test and PCR. The analysis showed that, on average, rapid diagnostic tests detected 41% (95% confidence interval = 26-66%) of PCR-positive infections. Data for the comparison of rapid diagnostic test to PCR detection at high transmission intensity and in adults were sparse. Prevalence measured by rapid diagnostic test and microscopy was comparable, although rapid diagnostic test detected slightly more infections than microscopy. On average, microscopy captured 87% (95% confidence interval = 74-102%) of rapid diagnostic test-positive infections. The extent to which higher rapid diagnostic test detection reflects increased sensitivity, lack of specificity or both, is unclear. Once the contribution of asymptomatic individuals to the infectious reservoir is better defined, future analyses should ideally establish optimal detection limits of new diagnostics for use in control and elimination strategies.

Estimation of Plasmodium falciparum Transmission Intensity in Lilongwe, Malawi, by Microscopy, Rapid Diagnostic Testing, and Nucleic Acid Detection

“…Specifically, submicroscopic malaria has been associated with older age, presumably due to partial immunity. 6,15,16 Although high levels of bed net usage during the study period suggested that bed nets may be partly responsible for this finding, bed net usage was not a risk factor for subpatent infection in our models, a finding consistent with prior reports. 16 Submicroscopic infections are also thought to be more common in settings of low transmission intensity.…”

“…1 Even if most subpatent infections in these young children are asymptomatic, they may represent a transmission reservoir that requires further study and may need to be addressed by ongoing malaria control efforts. 6 Age less than 5 years was a risk factor for subpatent malaria in our cohort, a finding that differs from other published reports. Specifically, submicroscopic malaria has been associated with older age, presumably due to partial immunity.…”

“…6,10 Although malaria prevalence as determined by PCR and RDT differed by only 16%, there was only moderate agreement between tests (kappa = 0.44), likely due in part to the large number of "false-positive" RDT results (Figures 1 and 2). "False-positive" RDT results have been described in the setting of persistent circulating HRP2 antigen after clearance of P. falciparum parasitemia, indicating not a failure of the assay itself but recently resolved malaria.…”

“…[3][4][5] Infections not detected by microscopy or RDT, often referred to as subpatent infections, can often be detected by nucleic acid detection methods. 6 Though infections detected by microscopy and RDT are likely responsible for the majority of transmission, further studies are needed to assess the impact of subpatent infections on the transmission reservoir. 7,8 In the context of vaccine trials, these low-level, subpatent parasitemias may confound estimates of transmission intensity used to study vaccine efficacy.…”

Molecular investigation of sub-microscopic and mixed Plasmodium species infection in North-Central Nigeria

“…In a systematic review, Okell et al [18] also found that older age groups were generally associated with increased sub-microscopic carriages. Our results are in tandem agreement with previous studies showing that molecular detection techniques have greater sensitivity and specificity than either microscopy for the identification of single and mixed species infections [23,[39][40][41][42], as well as sub-microscopic infections [11,43]. The detection of Plasmodium parasites at very low density parasitaemia is difficult by microscopy and thus requires a molecular approach especially for surveillance or epidemiological studies [44].…”