Since April 2020, several diagnostic companies have suggested that production dedicated to the most widely used malaria rapid diagnostic tests (RDTs) will be reallocated to covid-19 RDTs. In resource limited countries, RDTs are the main and often the only diagnostic tool for malaria. Together with the malaria community, we are concerned that the decision of the main manufacturer of malaria RDTs will have a negative impact on malaria programmes worldwide. Differential diagnosis of fever during the covid-19 pandemic without the aid of malaria RDTs will be even more challenging.
Without malaria RDTs, healthcare workers in high endemic countries will resort to presumptive treatment, risking inappropriate use of antimalarials and development of drug resistance. This will eventually lead to an increased demand for artemisinin-based combination therapy (ACT), which is already facing supply difficulties due to the covid-19 pandemic.
WHO has urgently called for minimizing the disruption to malaria programmes caused by covid-19, based on their modelling showing its potentially catastrophic consequences.
RDTs are relatively inexpensive and easier to use, develop, and manufacture than laboratory-based tests, but still require performance validation. An RDT is an instrument-free test device that consists mainly of a plastic cassette enclosing a test strip. There are different kinds of RDT products for various diseases in the market. In low- and middle-income countries (LMICs), the most important diseases that are diagnosed by RDT besides malaria include HIV, hepatitis B, hepatitis C, syphilis, cryptococcal disease, tuberculosis (TB-LAM test), and CD4 count (for advanced HIV disease). The price for an RDT varies per disease, with the reference price per test from the Global Fund pooled procurement mechanism for malaria RDT being the lowest at 0.22 to 0.40 USD.4 The malaria RDT is the only one for which companies have reallocated manufacturing lines. In comparison, the price for a covid-19 RDT ranges from 4 to 10 USD. There are some reports that plastic cassettes and strips to make RDTs are in short supply because of the rush by many companies to produce covid-19 RDTs.
Approaching these issues from a resource allocation perspective, the principle of utility (best outcomes) justifies that resources should be allocated to their capacity to do the most good. There has been a remarkable effort and speed in developing various SARS-CoV-2 test assays—detection of viral RNA by lab based or point of care PCR, detection of antigen by immunochromatographic tests or RDT and detection of antibody (IgM or IgG) by lab-based ELISA, IFA (immunofluorescence assay), or RDT. In particular, the number of RDTs that have been developed is impressive.
A smaller proportion of these tests have received regulatory approval for emergency use by stringent regulatory authorities. Independent evaluation of these RDTs are slowly becoming available. For antigen based RDT, overall sensitivity and specificity is reported to be 57.6% and 99.5%, respectively. For IgM/IgG antibody based RDT, the range is reported to be from 83% to 93% sensitivity and 80% to 100% specificity.
The standard test for diagnosing covid-9 is detection of viral RNA by PCR. RDTs are currently not recommended by WHO for diagnosing covid-19.
There are, however, continuing discussions on the possible use of RDTs, especially in LMICs where access to PCR testing remains a challenge.
We urge that all stakeholders and decision makers adopt an evidence-based approach to testing decisions, and not be driven by unproven public health approaches or commercial or political interests. Decisions that impact the allocation of resources should not be made by individuals or individual companies alone. Global public health policy and processes requires fairness and accountability by all stakeholders.
Credit: The BMJ Opinion