March 6 (UPI) -- Although the number of new cases of coronavirus continues to climb, well over half of those diagnosed with the disease have been declared fully recovered, according to data from the World Health Organization.
However, reports suggest a new subset of patients affected by the disease, known as COVID-19, may be emerging: A handful of the 60,000 or so people declared cured after treatment have been readmitted to hospitals days or weeks later because their symptoms have returned.
So far, most of these cases of reinfection have been in China, where the outbreak started, and research documenting these cases -- and confirming that they are, in fact, instances of reinfection -- remains lacking, experts say.
"I do not know of any cases at present where I would be definitively convinced that a person had fully recovered from the disease and had been reinfected as opposed to relapsed," William Hanage, assistant professor of epidemiology at the T.H. Chan School of Public Health at Harvard University, told UPI. "A lot of people are concerned about it, but I don't think we have any good evidence for it."
There is a distinction between relapse -- where a patient could be temporarily asymptomatic, only to have the flu-like symptoms of COVID-19 return -- and reinfection. For reinfection, a person would be ruled cured of the virus, and then catch it again, likely from another source, or perhaps with a different strain.
WHO guidance on COVID-19, which has continuously evolved as researchers learn more the disease, suggests it can be considered cured if a patient has no detectable levels of the virus on two consecutive polymerase chain reaction assay tests of swabs taken from their larynx or nasal passages.
Although most currently available tests for COVID-19 are based on PCR assays -- including one developed and distributed by U.S. health agencies and private manufacturers -- there are "subtle differences" between the approaches being used in different countries, Hanage said, which may be causing some of the confusion surrounding reinfection.
He cited the case of an Israeli passenger on the Diamond Princess cruise ship who was diagnosed with COVID-19 and treated in Japan as one example. Following treatment, and two successive negative PCR tests for the virus, he was declared cured and cleared to return to Israel.
When he arrived home, he was screened for the disease again, and the results came back positive.
"It wasn't that he was reinfected on the plane back to Israel," Hanage said. "This happened because of the slightly different way physicians in Japan administer these tests, compared to how it's done in Israel."
WHO guidance on testing and cured cases, however, is accurate based on the vast majority of the data on COVID-19 currently available, he added.
According to Justin Lessler, an associate professor at the Johns Hopkins Bloomberg School of Public Health, reinfection is possible with other coronaviruses -- and may be with COVID-19.
"Nothing is known specifically for COVID-19," he said, adding, that "it is unlikely reinfection could occur so rapidly that we would see it in the current epidemic wave."
If reinfection does occur, he said, "it is likely that subsequent infections would be more mild."
Complicating matters concerning recovery and reinfection further is the shortfall in COVID-19 testing capacity, particularly in the United States. The U.S. Centers for Disease Control and Prevention first began distributing its version of the PCR assay for the virus in mid-February, only to find out the test yielded inclusive results during quality control assessments a few days later.
The agency has scrambled to supply public health labs across the country with viable testing kits since the discovery, and the Food and Drug Administration has ramped up efforts with private diagnostics manufacturers to get similar products in place at hospitals, clinics and doctors offices.
Lessler said that while testing capacity in the United States "is expanding quickly," the shortage thus far has limited clinicians' ability at "capturing new cases, not validating recovery."
Hanage noted that as testing expands, "we're going to see a lot of cases coming out of the woodwork" -- and only once officials have a handle on how many people have actually been infected can they better understand issues like disease transmission and reinfection.
"The U.S. doesn't have sufficient testing capacity now," he said. "Even with 1.5 million tests available, as Vice President Mike Pence has promised, you still need 1.5 million pairs of hands of trained personnel to administer to them. It's tough enough at the moment for us to be figuring out exactly who is infected. The question of reinfection is almost a second-order issue."