LONDON -- Two British citizens remained in critical condition Saturday, breathing with the assistance of ventilators and surrounded by the world's leading experts on novichok poisoning, their odds of survival being closely tracked by Britain and Russia.
A police officer also underwent a precautionary test at a hospital to check for possible contamination related to the case, but police in Wiltshire said late Saturday that he had been cleared.
The couple, Dawn Sturgess, 44, and Charlie Rowley, 45, was exposed a week ago to traces of a Soviet-developed nerve agent. They likely came into contact with it by picking up a vial, syringe or ampule discarded by a would-be assassin who was in the city of Salisbury in southern England months ago to target a former Russian spy, police said.
Both victims had been in treatment after years of substance abuse, which compromises the liver's function as the body's detoxifier. That makes them more physically fragile than the three previous poisoning victims in Salisbury: the former spy, Sergei Skripal; his daughter, Yulia Skripal; and a British police officer who became sick after responding to the poisoning.
If either of the two dies, it would present British and Russian authorities with a new diplomatic scenario. Among the surprises of the March attack on Skripal and his daughter is that they did not die, most likely because they received a relatively small dosage. The police officer, Detective Sgt. Nick Bailey, also got better.
Their recoveries meant the attack fell off the front pages, allowing investigators to proceed with a slow, methodical search for evidence that might support their leading theory -- that Russian agents were behind the attack. The emergence of additional victims "will give it a renewed sense of urgency," particularly if one of them succumbs, said James Nixey, head of the Russia and Eurasia program at Chatham House, a research group in London.
Toxicologists say the first days after a poisoning are a crucial threshold for survival, as the body struggles to resynthesize an enzyme, acetylcholinesterase, which is inhibited by nerve agents. Novichok is believed to directly affect the brain's respiratory centers, and considerable time may pass before a patient can breathe on his own.
The poisoned couple were being treated at the same hospital that cared for the Skripals.
The hospital, in Salisbury, "has the most expertise in the world in dealing with people with this type of poisoning, but it very much depends on the state of the individual," said Alastair Hay, an emeritus professor of toxicology at the University of Leeds, England. "The fact that someone is frailer makes it more difficult, makes the outlook a little more bleak."
Scientific knowledge about novichok poisoning was close to zero in March, when the Skripals and Bailey fell ill, and medics expected them to die, they told the BBC in May. A paper published in May in the scientific journal Clinical Toxicology noted that while a large dose of a nerve agent could kill a patient within minutes, "mild or moderately exposed individuals usually recover completely."
Rowley's symptoms were observed more closely than those of Sturgess or of the Skripals, because a friend, Sam Hobson, was with him at the time.
The police officer given the all clear underwent "appropriate specialist tests," the Salisbury hospital said.
The hospital did not say whether the unidentified officer might have been exposed to novichok. But a statement said the officer initially sought medical advice at another hospital "in connection with the ongoing incident in Amesbury," where the latest victims developed symptoms.
The Salisbury hospital added that it "has seen a number of members of the public who have come to the hospital with health concerns since this incident started and none have required any treatment."
Information for this article was contributed by Ellen Barry of The New York Times, and by Gregory Katz of The Associated Press.
A Section on 07/08/2018