For a month, Rick Wright’s life has been in limbo. More than a dozen times, the Redwood City man has been tested for coronavirus — yet results swing back and forth, never assuring him that he is, or is not, harboring the virus.

“I’m sitting in a holding pattern,” said Wright, who never felt sick after being evacuated from the Diamond Princess cruise ship in Japan last month but was quarantined at a San Francisco hospital for eight days and then at home, to protect his family and community. “You’re happy one day, then sad the next. You just want to be cleared and have your life back.”

He’s not alone in this mystery. As testing increases, so do reports of inconclusive test results.

In general, the test for COVID-19 is very reliable, especially in people with symptoms. But the specter of so-called “false negatives,” of wrongly telling people they’re free of the virus when they are actually infected, looms menacingly over the effort to detect and control the disease as quickly as possible.

Because the virus can be transmitted by people without symptoms, ambiguous results can send infected people out into the community.

Last Saturday, after testing negative, a Stanford student left campus by car with five other students. But on Sunday, he learned that he tested positive, according to the Stanford Daily.

At The Forum at Rancho San Antonio retirement community in Cupertino, a male employee in the Skilled Nursing Unit was tested three times, six days apart. Twice he got good news. The third time, in an account that alarmed family members of the frail and elderly residents, he tested positive. According to conversations and emails sent to a family member, it has not been confirmed whether he somehow became infected during a hospital visit — or if his initial results were false.

The U.S. Centers for Disease Control and Prevention has not disclosed how sensitive its test is to detect very low levels of the virus.

When Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, was asked about it in a recent interview with the Journal of the American Medical Association, he hedged.

“If (the test is) positive, you absolutely can make a decision,” he said.

The uncertainty of test reliability means that quarantined passengers of the Grand Princess cruise trip at Travis Air Force Base are being held for a full 14 days — even though they test negative.

“I can almost see my house from here — but I can’t go there,” said Carl Mianecke, 76, of Napa, who tested negative but won’t be released from quarantine for another five days.  “I’ve resigned myself to it. I’m reading, watching TV and using my computer to work, but I would like to get home to make some real food.”

One of the first reports of suspect test results came during the initial outbreak of the disease in China. A young man with intermittent fever tested negative, then positive — then negative, twice.

“This case highlights that a single negative result of the test does not exclude COVID-19,” wrote Qinjian Hao and his team at Sichuan’s Center of Gerontology and Geriatrics, in a published report.

Such cases may risk “a potentially higher spread of the disease in the hospital and community because of delayed quarantine of the missed case,” the team warned.

The test is called Reverse Transcriptase PCR (RT-PCR). It measures tiny bits of viral RNA, a chain of cells that carry genetic information, that swim in oceans of cells in a patient’s sputum.

Test results may be inconclusive for several reasons, according to the expert virologists and the CDC.

There’s the possibility of simple technical errors, such as improper collection, handling or shipping. Or the test’s reagents (key chemical components of the kit) may be flawed, creating diagnostic inaccuracy.

It’s possible that the patient who tested negative, then later positive, is carrying levels of the virus that are so low they’re below the threshold of detection.

“Viral load goes up and down,” said Dr. Charles Chiu, director of UC San Francisco’s Viral Diagnostics and Discovery Center. “That’s the natural course of the disease. You can test a patient and they’ll be positive one day and negative the next day.”

There’s another possibility: If the patient isn’t showing symptoms, they may not have coughed up enough of the virus from their lungs into their upper respiratory tract, where test samples are taken.

It’s also possible the test can’t detect some strains of the virus, according to the CDC. RNA viruses like the COVID-19 pathogen have a lot of genetic variability. Although efforts were made to design test assays that target the parts of the viral genome that are shared by all strains, said the CDC, there might be a mismatch.

“We don’t have a test that can definitely say someone is not infected,” said Dr. John Swartzberg, a specialist in infectious disease and clinical professor emeritus at UC Berkeley’s School of Public Health.

“We know by the time symptoms appear, we will find it,” he added. “And we also know in a small number we can find it before symptoms. We don’t know how long before.

“We are asking more of the test than it can give us,” he said.

For Wright, the ambiguity has changed his life. To be safe, he remained alone at home, in self-quarantine, for 19 days. His wife, Kathy, who was also on the cruise but never tested positive, moved out of the home to stay with her sister; they waved to each other through the window.

His most recent test was taken eight days ago. Will it be definitive?

“I’m still waiting for results,” he said.