Traces of the virus behind COVID-19 have been detected in the semen of patients suffering from the deadly disease.
Chinese researchers tested 38 patients infected with SARS-CoV-2 and found the virus present in semen from six of them, according to a study published in journal JAMA Network Open.
A prior study in the US failed to find the virus in semen, but the patients in that study weren't looked at in some cases until three months after they'd been diagnosed.
The virus has also shown up in tests on patients' faeces and urine in other studies.
"Owing to the imperfect blood-testes/deferens/epididymis barriers, SARS-CoV-2 might be seeded to the male reproductive tract," the new study reads.
The authors say it's not clear yet if the disease can be transmitted sexually. Four of the six men were still "very sick" with the disease and unlikely to be engaging in sexual activity, and the other two had just recovered.
"If it could be proved that SARS-CoV-2 can be transmitted sexually in future studies, sexual transmission might be a critical part of the prevention of transmission, especially considering the fact that SARS-CoV-2 was detected in the semen of recovering patients," the study said.
One of the men whose semen tested positive had been showing symptoms of COVID-19 for 16 days.
"It may be wise to avoid sexual contact with men until they are 14 days without symptoms," Peter Schlegel of the American Society for Reproductive Medicine told the Associated Press.
University of Iowa microbiologist Stanley Perlman told the New York Times it could be that the virus present in semen is no longer infectious and otherwise harmless.
SARS-CoV-2 is known to spread via respiratory droplets, which are generally unavoidable during sex anyway.
"To avoid contact with the patient's saliva and blood may not be enough, since the survival of SARS-CoV-2 in a recovering patient's semen maintains the likelihood to infect others," the study said.
Initially 50 men were chosen to take part in the research, being aged 15 or over and admitted to Shangqiu Municipal Hospital between January 26 and February 16, but 12 of them "were unable to provide a semen specimen because of erectile dysfunction, being in a comatose state, or dying prior to recruitment".