Authorities say the 28-year-old woman died on Friday from pneumonia of an as-yet unestablished origin, in a case that has prompted international concern, including from US President Donald Trump.
Rospotrebnadzor, the watchdog, said in a statement on Tuesday that no infectious diseases had been reported among the staff of the same plague research institute in Irkutsk over the past 10 days and that extensive testing had found no microorganisms in the deceased woman's body linked to her work.
"A comprehensive set of anti-epidemic measures was immediately organised and implemented in full in accordance with public health legislation," the watchdog said.
"This included identifying the widest possible circle of individuals who had been in contact with the patient and arranging for them to be placed under medical observation in hospital with daily laboratory tests."
It said the results had revealed two cases of COVID-19 and two cases of rhinovirus infection, but that no pathogens causing other infectious diseases had been detected.
"None of the contacts showed any changes in their state of health associated with infectious disease," it added.
Elena Sofina, deputy head of the Shelekhov district near Irkutsk, where a local hospital was placed under quarantine, said what she called a "dangerous diagnosis" had not been confirmed.
She added that 60 per cent of those placed under quarantine as a precaution had already been released. Local media said around 200 people had previously been quarantined.
Kremlin spokesman Dmitry Peskov expressed appreciation for an offer of help on Monday from Trump, although without making clear if Moscow planned to accept it.
"It's always good when mutual assistance is offered," Peskov told reporters.
Trump on Monday described the situation as a "big problem for Russia". US Secretary of State Marco Rubio said on Tuesday it was incumbent on Moscow to share more information.
The World Health Organization in Geneva said on Tuesday that Russia had told it there were no cases of plague in the city of Irkutsk. Reuters could not immediately establish if this meant they could rule out plague in the lab worker's case.
In the town of Shelekhov, where the lab worker is reported to have died in hospital, locals said their lives had barely been disrupted although they said some people in shops had initially worn surgical face masks as a precaution.
A resident who gave her name only as Anna said the situation was calm and that people had been prepared for restrictions to be introduced, but that life had gone on pretty much as usual.
"Everyone had face masks at home and wore them for no more than 24 hours," she told Reuters.
Denis, another resident, said news of the lab worker's death had been widely discussed in the town and that the local hospital had temporarily stopped doing diagnostic tests but had since resumed normal business.
