Keep the quality high: the benefits of lot testing for the quality control of malaria rapid diagnostic tests

Background

The production and use of malaria rapid diagnostic tests (RDTs) has risen dramatically over the past 20 years. In view of weak or non-existing in vitro diagnostics (IVD) regulations and post-marketing surveillance (PMS) systems in malaria endemic countries, the World Health Organization, later joined by the Foundation for Innovative New Diagnostics, established an independent, centralized performance evaluation and Lot Testing (LT) programme to safeguard against poor quality of RDTs being distributed through the public health sector of malaria endemic countries. RDT performances and manufacturer quality management systems have evolved over the past decade raising questions about the future need for a centralized LT programme.

Results

Between 2007 and 2017, 6056 lots have been evaluated, representing approximately 1.6 Billion RDTs. A total of 69 lots (1.1%) failed the quality control. Of these failures, 26 were detected at receipt of the RDT lot in the LT laboratory, representing an estimated 7.9 million poor quality RDTs, and LT requesters were advised that RDTs were not of sufficient quality for use in patient management. Forty-three were detected after long-term storage in the laboratory, of which 24 (56%) were found to be due to a major issue with insufficient buffer volume in single use buffer vials, others predominantly showing loss of sensitivity. The annual cost of running the programme, based on expenses recorded in years 2014–2016, an estimated volume of 700 lots per year and including replenishment of quality control samples, was estimated at US$ 178,500 ($US 255 per lot tested).

Conclusions

Despite the clear benefits of the centralized LT programme and its low cost compared with the potential costs of each country establishing its own PMS system for RDTs, funding concerns have made its future beyond 2020 uncertain. In order to manage the risks of misdiagnosis due to low quality RDTs, and to ensure the continued safety and reliability of malaria case management, there is a need to ensure that an effective and implementable approach to RDT quality control continues to be available to programmes in endemic countries.

A review of the WHO malaria rapid diagnostic test product testing programme (2008-2018): performance, procurement and policy

Malaria rapid diagnostic tests (RDTs) emerged in the early 1990s into largely unregulated markets, and uncertain field performance was a major concern for the acceptance of tests for malaria case management. This, combined with the need to guide procurement decisions of UN agencies and WHO Member States, led to the creation of an independent, internationally coordinated RDT evaluation programme aiming to provide comparative performance data of commercially available RDTs. Products were assessed against Plasmodium falciparum and Plasmodium vivax samples diluted to two densities, along with malaria-negative samples from healthy individuals, and from people with immunological abnormalities or non-malarial infections. Three measures were established as indicators of performance, (i) panel detection score (PDS) determined against low density panels prepared from P. falciparum and P. vivax wild-type samples, (ii) false positive rate, and (iii) invalid rate, and minimum criteria defined. Over eight rounds of the programme, 332 products were tested. Between Rounds 1 and 8, substantial improvements were seen in all performance measures. The number of products meeting all criteria increased from 26.8% (11/41) in Round 1, to 79.4% (27/34) in Round 8. While products submitted to further evaluation rounds under compulsory re-testing did not show improvement, those voluntarily resubmitted showed significant increases in P. falciparum (p = 0.002) and P. vivax PDS (p < 0.001), with more products meeting the criteria upon re-testing. Through this programme, the differentiation of products based on comparative performance, combined with policy changes has been influential in the acceptance of malaria RDTs as a case-management tool, enabling a policy of parasite-based diagnosis prior to treatment. Publication of product testing results has produced a transparent market allowing users and procurers to clearly identify appropriate products for their situation, and could form a model for introduction of other, broad-scale diagnostics.

Melioidosis in patients with suspected tuberculosis in Cambodia: a single-center cross-sectional study

SETTING

Melioidosis-Burkholderia pseudomallei infection-is increasingly recognized in Cambodia, a country with a high incidence of tuberculosis (TB). Melioidosis and TB can be clinically indistinguishable.

OBJECTIVE

To quantify the proportion of patients with clinically suspected TB who had melioidosis by testing sputum for B. pseudomallei.

DESIGN

This was a prospective, 6-month cross-sectional single-center study at a Cambodian provincial referral hospital among patients with suspicion of TB who provided sputum specimens for testing. TB was diagnosed using sputum Xpert^® MTB/RIF molecular assay or culture; melioidosis was diagnosed using sputum culture for B. pseudomallei.

RESULTS

Of 404 patients evaluated for possible TB, 52 (12.9%, 95%CI 9.8-16.5) had TB. Four patients (1.0%, 95%CI 0.3-2.5) had melioidosis; none had concurrent TB or an existing medical risk factor for melioidosis, although two were farmers, an occupational risk factor.

CONCLUSION

One per cent of patients being evaluated for TB at a Cambodian provincial referral hospital had culture-proven respiratory melioidosis, a highly lethal infection. None had previously recognized medical conditions that would increase their risk of melioidosis. Testing for melioidosis should be considered in patients presenting with suspected TB in Cambodia.

Malaria rapid diagnostic test as point-of-care test: study protocol for evaluating the VIKIA Malaria Ag Pf/Pan

Background

Malaria rapid diagnostic tests (RDTs) are generally considered as point-of-care tests. However, most of the studies assessing the performance of malaria RDTs are conducted by research teams that are not representative of the classical end-users, who are typically unskilled in traditional laboratory techniques for diagnosing malaria. To evaluate the performance of a malaria RDT by end-users in a malaria-endemic area, a study protocol was designed and the VIKIA® Malaria Ag Pf/Pan test, previously evaluated in 2013, was re-evaluated by representative end-users.

Methods

Twenty end-users with four different profiles in seven communes in Kampot Province (Cambodia) were selected. A set of 20 calibrated aliquots, including negative samples, low positive samples (200 parasites/μL of Plasmodium falciparum and Plasmodium vivax) and high positive samples (2,000 parasites/μL of P. falciparum and P. vivax) was used. Testing was performed directly by the end-users without any practical training on the VIKIA® Malaria Ag Pf/Pan kit.

Results

All results obtained by the end-users were consistent with the expected results, except for the low positive (200 parasites/μL) P. vivax aliquot (35% of concordant results). No significant difference was observed between the different end-users. End-user interviews evaluating ease-of-use and ease-of-reading of the VIKIA® Malaria Ag Pf/Pan kit recorded 159 positive answers and only one negative answer. Out of 20 end-users, only one considered the test was not easy to perform with the support of the quick guide.

Conclusions

The data presented in this study clearly demonstrate that the performance of the VIKIA® Malaria Ag Pf/Pan test when performed by traditional end-users in field conditions is similar to that obtained by a research team and that this RDT can be considered as a point-of-care tool/assay. Furthermore, the protocol designed for this study could be used systematically in parallel to conventional evaluation studies to determine the performance of malaria RDTs in field conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0633-3) contains supplementary material, which is available to authorized users.

Circulating antibodies against Plasmodium falciparum histidine-rich proteins 2 interfere with antigen detection by rapid diagnostic tests

BACKGROUND

Rapid diagnostic tests (RDTs) for detection of Plasmodium falciparum infection that target P. falciparum histidine-rich protein 2 (PfHRP2), a protein that circulates in the blood of patients infected with this species of malaria, are widely used to guide case management. Understanding determinants of PfHRP2 availability in circulation is therefore essential to understanding the performance of PfHRP2-detecting RDTs.

METHODS

The possibility that pre-formed host anti-PfHRP2 antibodies may block target antigen detection, thereby causing false negative test results was investigated in this study.

RESULTS

Anti-PfHRP2 antibodies were detected in 19/75 (25%) of plasma samples collected from patients with acute malaria from Cambodia, Nigeria and the Philippines, as well as in 3/28 (10.7%) asymptomatic Solomon Islands residents. Pre-incubation of plasma samples from subjects with high-titre anti-PfHRP2 antibodies with soluble PfHRP2 blocked the detection of the target antigen on two of the three brands of RDTs tested, leading to false negative results. Pre-incubation of the plasma with intact parasitized erythrocytes resulted in a reduction of band intensity at the highest parasite density, and a reduction of lower detection threshold by ten-fold on all three brands of RDTs tested.

CONCLUSIONS

These observations indicate possible reduced sensitivity for diagnosis of P. falciparum malaria using PfHRP2-detecting RDTs among people with high levels of specific antibodies and low density infection, as well as possible interference with tests configured to detect soluble PfHRP2 in saliva or urine samples. Further investigations are required to assess the impact of pre-formed anti-PfHRP2 antibodies on RDT performance in different transmission settings.

Performance of the CareStart™ G6PD deficiency screening test, a point-of-care diagnostic for primaquine therapy screening

Development of reliable, easy-to-use, rapid diagnostic tests (RDTs) to detect glucose-6-phosphate dehydrogenase (G6PD) deficiency at point of care is essential to deploying primaquine therapies as part of malaria elimination strategies. We assessed a kit under research and development called CareStart™ G6PD deficiency screening test (Access Bio, New Jersey, USA) by comparing its performance to quantitative G6PD enzyme activity using a standardized spectrophotometric method ('gold standard'). Blood samples (n = 903) were collected from Cambodian adults living in Pailin province, western Cambodia. G6PD enzyme activities ranged from 0 to 20.5 U/g Hb (median 12.0 U/g Hg). Based on a normal haemoglobin concentration and wild-type G6PD gene, the normal values of G6PD enzymatic activity for this population was 3.6 to 20.5 U/g Hg (95(th) percentiles from 5.5 to 17.2 U/g Hg). Ninety-seven subjects (10.7%) had <3.6 U/g Hg and were classified as G6PD deficient. Prevalence of deficiency was 15.0% (64/425) among men and 6.9% (33/478) among women. Genotype was analyzed in 66 G6PD-deficient subjects and 63 of these exhibited findings consistent with Viangchang genotype. The sensitivity and specificity of the CareStart™ G6PD deficiency screening test was 0.68 and 1.0, respectively. Its detection threshold was <2.7 U/g Hg, well within the range of moderate and severe enzyme deficiencies. Thirteen subjects (1.4%, 12 males and 1 female) with G6PD enzyme activities <2 U/g Hg were falsely classified as "normal" by RDT. This experimental RDT test here evaluated outside of the laboratory for the first time shows real promise, but safe application of it will require lower rates of falsely "normal" results.

Global sequence variation in the histidine-rich proteins 2 and 3 of Plasmodium falciparum: implications for the performance of malaria rapid diagnostic tests

Background

Accurate diagnosis is essential for prompt and appropriate treatment of malaria. While rapid diagnostic tests (RDTs) offer great potential to improve malaria diagnosis, the sensitivity of RDTs has been reported to be highly variable. One possible factor contributing to variable test performance is the diversity of parasite antigens. This is of particular concern for Plasmodium falciparum histidine-rich protein 2 (PfHRP2)-detecting RDTs since PfHRP2 has been reported to be highly variable in isolates of the Asia-Pacific region.

Methods

The pfhrp2 exon 2 fragment from 458 isolates of P. falciparum collected from 38 countries was amplified and sequenced. For a subset of 80 isolates, the exon 2 fragment of histidine-rich protein 3 (pfhrp3) was also amplified and sequenced. DNA sequence and statistical analysis of the variation observed in these genes was conducted. The potential impact of the pfhrp2 variation on RDT detection rates was examined by analysing the relationship between sequence characteristics of this gene and the results of the WHO product testing of malaria RDTs: Round 1 (2008), for 34 PfHRP2-detecting RDTs.

Results

Sequence analysis revealed extensive variations in the number and arrangement of various repeats encoded by the genes in parasite populations world-wide. However, no statistically robust correlation between gene structure and RDT detection rate for P. falciparum parasites at 200 parasites per microlitre was identified.

Conclusions

The results suggest that despite extreme sequence variation, diversity of PfHRP2 does not appear to be a major cause of RDT sensitivity variation.

[The management of stroke in Phnom Penh, Cambodia]

Stroke ranks first among nervous pathologies in Kampuchea. It's a main cause of disability and mortality in our country. We conducted a prospective study including 100 patients hospitalized in the service of general medicine at the Calmette hospital in Phnom Penh. We analyzed the principal risk factors, clinical signs, nature of stroke, complications and markers of the vital and functional prognosis. This work shows the difficulties encountered in the initial care of stroke: delay or absence of hospitalization, cost of complementary examinations to be carried out to determine the nature and the aetiology of stroke and very low level of follow-up to ensure secondary prevention and functional rehabilitation. It can be explained in part by the socioeconomic and cultural level. Research like this one which assesses local needs for stroke prevention, treatment and rehabilitation should be conducted in developing countries to inform the planning and allocation of health care resources in order to reduce the burden of illness associated with stroke. The progressive improvement of the medical structures, and of the socioeconomic and cultural level will facilitate stroke care management.

Large sequence heterogeneity of the small subunit ribosomal RNA gene of Plasmodium ovale in cambodia

Plasmodium ovale malaria has been reported in various countries in southeast Asia, but never in Cambodia. Using a species-specific polymerase chain reaction (PCR) targeting the small subunit (SSU) ribosomal RNA (rRNA) gene, we detected P. ovale in nearly 4% of the inhabitants of a northeastern Cambodian village. Plasmodium ovale was associated with at least one other Plasmodium species, and two quadruple infections were detected. The diagnosis was confirmed by microscopy and by SSU rRNA PCR product sequencing. The sequences shared 96-99% identity with published sequences, and displayed a substantial heterogeneity with 2-4 different haplotypes per sample. Nine distinct SSU rRNA haplotypes were identified, including seven novel variants. Phylogenetic analysis showed two major genetic clusters, suggesting amplification of two distinct gene sets and/or P. ovale variants from each sample. Our data indicate that P. ovale was overlooked in Cambodia until now, and call for the implementation of larger prevalence surveys and accurate diagnosis methods in this country.