An Indian resident who tested positive for Ebola—and was cured—has landed in Delhi from Liberia.

The 26-year-old man is being isolated in a facility at Delhi’s Indira Gandhi International airport, The Times of India reports.

According to the Times, the man had already been treated for Ebola in West Africa, currently does not have symptoms and tested negative for the virus before he flew. However, his semen tested positive for the virus.

He had a medical clearance certificate from the Liberian government saying the had been treated and was confirmed negative from blood tests—that would deem him Ebola-free, according to the World Health Organization and Centers for Disease Control and Prevention (CDC). His blood also tested negative in India. Semen can test positive after clinical clearance for up to three months, according to the CDC. The agency recommends abstinence from sex—including oral sex—for at least three months. If abstinence cannot be followed, the CDC recommends condoms to prevent disease spread.

The patient in India is being kept in isolation in a health facility at the airport until his semen tests negative.

It’s not likely that he poses a threat, given the negative test from his blood, but experts have long been concerned that a spread of Ebola in India could be devastating given the population size.

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