The regional hospitals and remote medical centers and clinics of the Costa Rican Social Security Fund (CCSS) will soon begin to test for the virus that causes the covid-19. However, the test they will use is different from the one already used in other public hospitals in the metropolitan area and in the Instituto Costarricense de Investigación y Enseñanza en Nutrición y Salud (Inciensa) – Costa Rican Institute for Research and Teaching in Nutrition and Health.
Both tests work with Polymerase chain reaction (PCR) technology, which allows high reliability; but in regional hospitals, a test called GeneXpert will be used, which allows faster results, without the need for analysis by a molecular biology laboratory.
GeneXpert technology produced by the California-based firm Cepheid, can process nose swab samples in a mere 45 minutes.
This modality is more convenient for remote medical centers that do not have a molecular biology laboratory and only in case of doubt, the sample needs to be sent to be corroborated by a conventional PCR test.
Last Sunday, Mario Ruiz Cubillo, medical manager of the CCSS, announced at a press conference that this Monday, GenXpert equipment will begin to be distributed to regional hospitals and medical centers to increase the country’s diagnostic capacity.
“We are doing everything possible to make the tests of a high level of reliability,” said Ruiz.
He added: “even centers such as the CAIS de Cañas, or the Monseñor Sanabria Hospital (Puntarenas), the San Carlos Hospital, the Valverde Vega Hospital (San Ramón) will be able to carry out these tests and this will allow us to have better care for possible patients and treat them if necessary ”.
GeneXpert technology is not new, what is new is its application for the detection of SARS-CoV-2, the virus that causes covid-19. Previously, it has been used to detect tuberculosis.
PCR remains key
The CCSS already has the first reagents for the GeneXpert tests, but their use is intended for regions outside the Greater Metropolitan Area (GAM).
The differences between conventional tests and faster tests are part of the reasons.
“The GeneXpert uses disposable cartridges. It is an integrated principle of PCR. All chemicals come inside the cartridge. In conventional PCR there are three kits: extraction, reverse transcription and amplification, they are all needed to be able to do the test. The GeneXpert has them all in a single cartridge,” explained bioinformatics and genetics specialist Allan Orozco.
“I find them very good for rural areas where you have nothing. It works anywhere; in the middle of the jungle, you put it under a tree and with a battery it works. Standard PCR doesn’t like the jungle, only formal clinical laboratories,” he added.
However, due to its high demand worldwide, large quantities is difficult to obtain and stock in the country.
“The problem is the following: these tests do not work without cartridges and the company is sending very few to the country; about 600 or 700 per week. There is a voracious demand in international markets,” Orozco explained.
Another vital difference is that, unlike standard tests that determine in a matter of hours whether the virus is present or not, GeneXpert tests can give three possible results: 1- positive, 2- probably positive, and 3-negative .
If this rapid test yields a likely positive conclusion, conventional PCR should be run to determine the definitive answer. In that case, the final diagnosis can be issued by the Inciensa or some molecular biology laboratory of a CCSS hospital.
Ruiz, indicated that this test will be applied to those who qualify as a suspicious case.
“The test is done on patients who meet established diagnostic criteria to be candidates for it,” said the medical manager.
Among those criteria are: having respiratory symptoms that are not explained by any other cause, or loss or decrease in the sense of smell or changes in taste, or people whose treating doctor sees that the test should be performed.