Scientists across the world are trying to piece together a perplexing puzzle: how exactly the coronavirus affects the body, and how it spreads from person to person.
In recent months, they have learned that the virus can live on some surfaces for three days and that it can stay suspended in tiny aerosolized droplets for about 30 minutes. The virus has been detected in saliva, urine and feces.
Now researchers in China have found that the coronavirus, or bits of it, may linger in semen. But the paper, published Thursday in JAMA Network Open, a peer-reviewed open-access medical journal, does not prove that the virus can be sexually transmitted.
The doctors tested semen from 38 patients at Shangqiu Municipal Hospital in Henan province in central China. All the subjects, who ranged in age from 15 to 59, had previously tested positive for the coronavirus.
Researchers detected genetic material from the coronavirus in the semen of six patients, around 16%. Four patients with positive semen samples "were at the acute stage of infection," wrote Dr. Weiguo Zhao of the Eighth Medical Center of Chinese People's Liberation Army General Hospital in Beijing and Dr. Shixi Zhang of the Shangqiu Municipal Hospital in Henan.
Two were recovering, "which is particularly noteworthy," they added. It had been 16 days since one of the men had first shown symptoms, according to a chart featured in the study.
Zhao and Zhang could not immediately be reached for comment.
From the early days of the outbreak, public health experts have been saying that though the coronavirus could be transmitted through kissing, they did not believe it could be sexually transmitted.
The new finding does not contradict this. If semen tests positive for the coronavirus, that does not mean that infectious virus is present, said Dr. Stanley Perlman, a professor of microbiology, immunology and pediatrics at the University of Iowa, who was not involved in the study.
"This is an interesting finding, but it must be confirmed that there is infectious virus - not just a virus product in the semen," he said. The semen tests may have detected only fragments of viral RNA, he added.
Perlman pointed out that unlike Zika, which is carried in the blood, the coronavirus primarily infects people via an oral or a nasal pathway.
At the moment, there still is no evidence that a person could be infected by sexual contact or an intrauterine insemination procedure with infected sperm. Transmission during sex is far more likely by the usual means: infectious respiratory droplets.
Still, some doctors are eager for more research into the coronavirus and semen for other reasons. If scientists were to find infectious virus present in semen, there may be implications for the safety of oral sex and the handling of semen.
Across the world, many fertility clinics have stopped accepting new patients - not only to reduce patient traffic, but also because of concerns that donor sperm might infect women trying to get pregnant.
There's an urgent need for more studies, noted Dr. Amir Kashi of the Shahid Beheshti University of Medical Sciences in Tehran, Iran, in a paper titled, "COVID-19 and Semen: An Unanswered Area of Research."