The virus which causes COVID-19 has been detected in blood donated by someone who recovered from the disease nearly six weeks earlier.
And while doctors here say there's probably no risk to recipients, there's concern asymptomatic patients, or people who've previously been infected and recovered, pose a "risk to the safety of the blood supply".
According to a report in journal Annals of Internal Medicine, published by the American College of Physicians, the donor "had symptoms of upper respiratory infection in early March, including body aches and sore throat without fever".
They didn't get tested for COVID-19 at the time, and fully recovered.
In mid-April, the operators of the unnamed blood donation service tested donations they'd received for SARS-CoV-2, the virus behind COVID-19 and came up with a positive result.
"The confirmation of [the virus in the blood] more than one month after symptom resolution is concerning in light of current guidelines, which do not recommend SARS-CoV-2 screening in the general... donor population," they said.
"In this case, plasma viral RNA was reproducibly detected at a time point that exceeded recommendations for deferral based on time since symptom resolution (14 days)."
It's not known at this stage whether the disease can be spread via blood transfusion.
The NZ Blood Service told Newshub there's "no risk" as "there are no cases of respiratory viruses being transmitted by transfusion".
"While traces may remain in the bloodstream, there is no evidence that they can pass on infection," a spokesperson said.
Regardless, the Blood Service says anyone who's been overseas or potentially exposed should wait 28 days before donating.
The doctors in the case report said even if SARS-CoV-2 can be transmitted via the blood, the patient in this case only had a small amount so it probably wasn't a risk - but they're not taking any chances, with much about the virus still a mystery.
"Furthermore, the risk for transmission of other transfusion-transmitted viral infections, such as HIV-1, is correlated with virus load, indicating that if bloodborne transmission is possible, the low level of SARS-CoV-2 detected in this case was unlikely to be transmitted.
"Taken together, these data suggest that this donor posed a limited but uncertain risk to the safety of the blood supply."
The donation service which took the sample is now recommending donors who may have been exposed to the virus wait 56 days before donating blood again, up from the previous 28.
The NZ Blood Service said its stocks remain at "healthy levels", as people kept giving during the lockdown.
"We continue to encourage people to book appointments to donate as the need for blood is constant, as blood only lasts 35 days."
