The odd result highlights that Venezuela is going about testing its citizens unlike any other country: Mass deployment of a rapid blood antibody test from China that checks for proteins developing a week or more after someone is infected, while using on a much smaller scale the gold-standard nasal swab exam that detects the virus from the onset.
Doctors warn Venezuela’s approach could be missing untold numbers who test negative because they do not yet have high antibody levels but could nonetheless have the virus and be spreading it to others.
“We could be letting people slip under the table who have the infection,” said a doctor at the University of the Andes medical school, speaking on condition of anonymity for fear of reprisals. Physicians in and outside Venezuela say the antibody test is best utilized not as a diagnostic tool but to help assess how widespread the virus is in a community, when to lift quarantines or to identify potential plasma donors.
Yet defenders say Venezuela, mired in a profound economic and public health crisis that began years before the pandemic, has little choice but to rely on it as a first-line test. The nation is one of the least-prepared to confront the pandemic, with hospitals routinely lacking basics like running water, gloves and masks, and thousands of physicians having emigrated in recent years.
“With limited staff and financial resources, the country has to explore other options such as the rapid test,” Dr. Gerardo de Cosío, head of the Venezuela office of the Pan American Health Organization and the World Health Organization, told The Associated Press.
De Cosío, who has worked with government health officials on the nation’s strategy, said Venezuela is further hampered in terms of machines and personnel available to process nasal swab tests, which can take hours.
The antibody test comes from Chinese biotech company Wondfo and takes about 20 minutes to yield a result, health workers say. Those who test positive are then given a nasal swab exam to confirm, a process that can take days because a single lab in Caracas is processing almost all of them. Those who come back negative but have numerous coronavirus symptoms or were in contact with an infected person also undergo the swab test.
Only swab-test positives are added to the country’s official case count, several physicians told AP. Government officials, who did not respond to a request for information on the matter, have not said exactly who is getting tested, but doctors and TV images indicate subway workers, hospital staff and returning fishermen and migrants are among those being tested. It's not clear how many positives the antibody tests have yielded.
“I’m not sure I would choose to do exactly what they’re doing,” said Dr. Angela Caliendo, a professor of medicine at Brown University and board member of the Infectious Diseases Society of America. Still, she too noted Venezuela’s resource difficulties and said “they have a lot of these tests that are inexpensive to run (and) they’re getting quite a bit of data.”
Bruised by years of economic calamity and more recently by U.S. sanctions, President Nicolás Maduro appealed for international help in March even before the country's first confirmed case. Allies Beijing, Havana and Moscow plus the United Nations sent tests, medical gear and, in Cuba’s case, doctors.
One of the largest shipments from China arrived at the end of last month carrying a half-million antibody tests. As of March 31, according to the U.N. Office for the Coordination of Humanitarian Affairs, Venezuela had done just 1,779 swab tests with an 8% positive rate.
In the two weeks since, authorities say they have conducted more than 250,000 tests, and Pan American Health Organization figures show all but about 3,000 were antibody tests. “We are at the forefront of Latin America,” Vice President Delcy Rodríguez declared.
But it’s an inexact comparison since the rest of the region relies on the genetic swab test. Neighboring Colombia, for example, has conducted about 50,000 tests, all swabs. Mexico health undersecretary Hugo López-Gatell has expressed disdain for the antibody tests, saying they’re about as reliable as a coin toss. Chile has also ruled out using them as a diagnostic tool.
“It’s complementary to what we are doing,” Chilean Health Minister Jaime Mañalich said. “But it doesn’t work for a general screening of the population.” The Wondfo test has approval from an EU regulating agency, but some physicians warn that many exams are being pushed to market without rigorous testing and it’s not yet known how sensitive they are.
Venezuelan officials say 143 coronavirus cases were confirmed during the second half of March, and 61 since the dramatic ramping up with antibody tests. “What’s seen normally is that when a country increases testing, cases increase,” said Enrique Acosta, of the Max Planck Institute for Demographic Research in Germany. “I look at (Venezuela's) numbers with concern.”
Experts say the antibody tests do have value as a broader public health tool and are likely to be used more around the world in the months ahead. “It does give you a snapshot of what is going on with the virus,” said Dr. Carl Fichtenbaum, an infectious disease specialist at the University of Cincinnati, but "it's probably a bottom number.”
Some physicians believe it’s possible the virus has not yet begun to spread widely in Venezuela, which could help explain the still-low case numbers. The country was largely cut off from the world even before the pandemic, and severe gasoline shortages make even domestic travel difficult.
A strict quarantine – the first nationwide shutdown in Latin America – could also be slowing the virus. In the coastal state of Nueva Esparta, a military plane arrives about every three days to pick up nasal specimens for transport to the lab in Caracas. Until results come back, doctors must rely on potentially imperfect information from antibody testing.
“It’s all we have right now,” said Dr. Elesban Gómez, head of the state’s public health unit. “It’s the only thing to guide us.”
Christine Armario reported from Bogota, Colombia. Associated Press writers Eva Vergara in Santiago, Chile, and Christopher Sherman in Mexico City contributed to this report.