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FIND Assesses Rapid Tests for Ebola While Cepheid GeneXpert Being Used in Current Outbreak


NEW YORK (360Dx) – The Foundation for Innovative New Diagnostics (FIND) recently evaluated four rapid immunoassay-based tests that can be used for screening and triaging of patients suspected of having Ebola, revealing variable sensitivities and specificities.

In the Ebola outbreak currently raging in the Democratic Republic of Congo, an assay from Cepheid is also being used to simplify the PCR-based confirmatory testing workflow.

The ongoing outbreak in DRC has already led to more than 1,000 cases and nearly 700 deaths, and many global aid agencies are concerned about the potential of a "perfect storm" for Ebola transmission — there is a large number of uprooted refugees in the region who have been forced into temporary camps and are crossing borders due to a violent political upheaval. They lack trust in authorities, according to a recent assessment, and are becoming more inaccessible to medical aid.

Similarly, the medical authorities and local infrastructure that may wish to use Ebola assays to stem this outbreak need to have trust in their performance.

As Cassandra Kelly-Cirino, director of Emerging Threats at FIND, noted in an interview, to be able to get an emergency use authorization (EUA) or emergency use assessment and listing (EUAL), either from the US Food and Drug Administration or World Health Organization, a company really doesn't need very much data. "You can use negative blood samples that have been spiked with a pathogen, or maybe just even nucleic acid," Kelly-Cirino said.

In order to clarify how certain tests perform, FIND decided that a comparative assessment of rapid Ebola tests "would provide some deeper data for regulatory bodies, and for countries, to be able to understand what are they procuring and how to use the tests."

The FIND evaluation compared five Ebola lateral flow rapid diagnostic tests (RDTs) from four diagnostics makers — SD Biosensor, Intec, Corgenix, and Senova — on 320 patient samples collected during the Ebola outbreak in West Africa that began in 2014.

As described in a PLoS One study published earlier this month, FIND scientists compared the tests to a gold-standard Ebola RT-PCR test from Altona, and found sensitivities ranging from approximately 80 percent to 98 percent, and specificities ranging from 80 percent to 100 percent. However, no single RDT had both high sensitivity and high specificity.

Separately, the scientists also compared another PCR-based test — a non-commercial test commonly called the Trombley assay — to the Altona Ebola test, and found that the Trombley RT-PCR assay had a lower limit of detection than the Altona test with some RDTs having higher sensitivity than the Altona assay when the Trombley assay was used as the bench mark, according to the study and also mirroring previous results with the Altona test.

The FIND scientists interpreted their results to mean that all of the tested RDTs "may be considered suitable for use in an outbreak situation," such as for so-called rule-out testing in communities, or for things like testing cadavers to deem them safe for local burial customs.

In general, rapid tests may be critical to stem an outbreak in Ebola infections for a number of reasons. They can be used to rule out infection or triage sick people to quarantine, but PCR-based testing is required to confirm an infection.

Unfortunately, outbreak settings are very difficult environments in which to do the lab work required for PCR, Kelly-Cirino said, particularly to perform the extraction protocols on potentially infectious blood samples that are required for manual PCR.

Most responders are doing this lab work in "a hot zone, so right where the patients are, which means that they've got pop up, temporary laboratory facilities, which don't necessarily have air conditioning, and they're in various layers of personal protective equipment," she said, adding, "It's also a very stressful situation." To make matters worse in the DRC outbreak, aid workers there are not necessarily safe due to the conflict in the region.

The stress can also come in part from the fact that the Ebola virus is highly contagious and can be transmitted in body fluids, and there is no treatment for the infection.

It also has a very high case fatality rate. The 2014 outbreak in West Africa — which purportedly began with one 18-month-old boy in rural Guinea who contracted Ebola after playing near a tree where infected bats were roosting — sickened approximately 20,000 people in three countries, and led to more than 11,000 deaths, according to the US Centers for Disease Control and Prevention. The agency also estimated 30,000 children were orphaned during the outbreak, and resources were diverted from vaccination programs, leaving them more vulnerable to other diseases.

Agencies like WHO and FDA supported a number of companies making tests available through emergency use authorizations during the 2014 West Africa Ebola outbreak.

"Once it was identified as a PHEIC — a Public Health Emergency of International Concern — there were a lot of companies stepping up and saying, 'We've manufactured a test, we've got something that should go into countries,'" Kelly-Cirino said. A lot of industry players were also calling countries directly advocating use of their tests, so FIND "felt very strongly that there was a comparative assessment needed that went beyond the original, often limited, data that most industry companies had on their tests."

For FIND, it is also critical to understand the performance of lateral flow assays so that agencies can understand how to implement them to triage patients, Kelly-Cirino said.

"Countries or responding agencies like MSF or WHO – those going in and coordinating the responses – can take the data we provide and decide, based on sensitivities and specificities of the test, how they want to implement it within the region," she said.

Newer RDTs and the rise of rapid, automated PCR

When the PLoS study was done, there were only a limited number of RDTs available, Kelly-Cirino noted, but there are now others available that need to be tested, as well.

"One of the things that we've been discussing with a lot of different groups including WHO, the Bill & Melinda Gates Foundation, and different government donors, is the need to look at all the currently available lateral flow assay tests and do a head-to-head comparison of them. … [C]ountries aren't quite clear about which ones they should take up and implement because the performance data are so limited," she said.

Positive tests, however, require confirmation, in part because sequestering a feverish person into quarantine together with Ebola patients could be a death sentence should it turn out her fever was caused by malaria or typhoid.

Testing for Ebola using PCR is the gold standard but results reporting in outbreak scenarios has previously taken up to a week. According to Doctors Without Borders, a medical aid agency also known as Médecins Sans Frontières (MSF), in the current Ebola outbreak in DRC, the wait time has shrunk to hours due to adoption of the Cepheid GeneXpert system, enabling Ebola testing to be done rapidly and close to transmission zones. "One caveat is that many patients may test negative for the first few days of symptoms, so a negative Ebola test needs to be repeated after 72 hours if Ebola is strongly suspected," the group said on its website.

A representative at Cepheid confirmed that the firm's Ebola test, which runs on the rapid, automated GeneXpert system, is being used in the field in DRC currently. A report last summer noted there were 150 instruments being used in DRC outbreak at that time, but the Cepheid representative said that number is now higher.

Cepheid was awarded $3.3 million from the Paul G. Allen Family Foundation and the Bill & Melinda Gates Foundation in late 2014 to develop the test, and it was subsequently cleared for emergency use by the FDA and WHO. It has also shown good performance results in published studies.

A 2016 evaluation of the test in Sierra Leone, published in PLoS Medicine, found the test had "excellent performance compared to an established RT-PCR benchmark" on whole blood and buccal swab samples in a field laboratory setting.

And, a PLoS Neglected Tropical Diseases evaluation in Liberia published last year described a mobile laboratory co-located at an Ebola treatment unit that was equipped with a GeneXpert molecular diagnostic platform. The laboratory "contributed significantly to the EVD response in Liberia," including supporting surveillance, outbreak detection, contact tracing, and management of confirmed cases, the study authors noted. And, importantly, the laboratory was run by local laboratory technicians rather than international experts on short missions, making it a more sustainable option in prolonged outbreaks.

"The redeployment and strategic placement of these GeneXpert instruments to complement [Ebola] isolation facilities throughout the country has strengthened preparedness and response capabilities" for future outbreaks in Liberia, the authors said.

Overall, adopting RDTs more widely and combing them with the Cepheid system could facilitate early detection and isolation, according to a recent commentary in The Lancet, although the authors noted that the "exact strategy or combinations used should ultimately be determined by teams on the ground who have granular understanding of the communities and settings involved."

As a sign of things to come, FIND last year initiated a new Diagnostics for Epidemic Preparedness strategy that aims to pair assay developers with instrument manufacturers. As part of this program, FIND awarded funding to assist in porting a Lassa fever assay developed by Altona onto a new product called the Flex cartridge system being developed by Cepheid for its GeneXpert platform.