April 1979: a filter came off a machine in a closed Soviet city.

April 2, 1979.

Sverdlovsk was a closed city. It sat on the eastern slope of the Urals, roughly nine hundred miles from Moscow, and it built things the state did not advertise: tanks, turbines, heavy machinery, artillery. More than a million people lived there. Foreigners did not visit. It was the city where the last tsar and his family had been shot in a basement, sixty-one years earlier, and it had been renamed after the Bolshevik who signed off on it.

The southern district was called Chkalovsky. Apartment blocks, a pipe plant, a ceramics factory that ran shifts around the clock. On the other side of the road from the ceramics factory stood a wall, and behind the wall a military compound with its own barracks and its own gate. The men at the ceramics factory smoked in the yard between shifts and looked at it every working day of their lives.

What went on inside was the manufacture of anthrax. Bacillus anthracis was grown in fermenters, concentrated, dried, and milled into a powder fine enough that the particles would hang in the air and travel to the bottom of a lung. The Soviet Union had signed the Biological Weapons Convention in 1972. Production at Sverdlovsk continued after the signature, and the facility was one node in a program that ran across several republics.

The protection between that powder and the city was mechanical. Air pulled out of the production rooms went through filters before it went up the stack. The filters clogged. They were changed on shift.

The account that later came out of the program, from a former deputy director who defected to the United States, describes a routine failure. A filter was taken off a drying machine during one shift. A note was written to say the machine should not run until a new filter was fitted. The note did not reach the man who took over. The machine was switched back on and it ran for hours.

The wind that day came out of the north-northwest. It carried across the road, over the ceramics factory yard, over the pipe plant, over the apartment blocks and the bus stops and the market, and out past the edge of the city into open country where there were villages and sheep.

Nothing happened for the rest of the day. Nothing happened the next day. Anthrax spores in a lung do not announce themselves. They sit in the small airways, get carried into the lymph nodes in the chest, and germinate there on their own schedule, which can be two days or can be several weeks. The men on the night shift at the ceramics plant went home, slept, and came back.

The first of them started feeling sick within the week. It presented like a hard flu. Fever, headache, an ache in the chest, a dry cough, tiredness. Some of them stayed home and some of them worked through it. Then, in many of the cases, there was a stretch of hours where they felt better and said so. After that came the second phase. Breathing became difficult and then impossible, the blood pressure fell away, and the patient went into shock. Men who had been at their machines four days earlier were dead within a day or two of being admitted. The pattern held across the cases: mostly men, mostly working age, almost no children among them.

The sick were brought to a hospital ward in the city. The doctors there were told what they were dealing with: anthrax from contaminated meat, the intestinal form, which occurs when a person eats an infected animal. Two pathologists, Faina Abramova and Lev Grinberg, did the autopsies. What they found in body after body was not intestinal. The tissue in the center of the chest, between the lungs, was swollen and black with blood. Over the surface of the brain there was a layer of hemorrhage that pathologists in the older literature had called the cardinal's cap. Those findings came from spores taken in through the lungs. Abramova had never seen a case. She had read the descriptions.

Officers arrived and collected records. Hospital charts, autopsy protocols, the paperwork of the outbreak. Abramova kept specimens back. Tissue in paraffin blocks and in jars of preservative, taken from the bodies she had opened, held out of the collection and put away. She said later that a pathologist keeps specimens. The samples went onto a shelf.

The city was cleaned. Street crews hosed down roads and building fronts and the trees. Roofs were washed. Stray dogs were shot on the grounds that dogs had been eating tainted meat. Tens of thousands of residents in the southern districts were vaccinated against anthrax, and the vaccinations were presented as a precaution against the outbreak in the food supply. Posters went up warning people not to buy meat from unauthorized sellers. Newspaper notices repeated it. The deputy minister of health for the Soviet Union, Pyotr Burgasov, was among the officials who stated the meat explanation publicly and continued stating it for years.

The dead were buried in a separate section of a cemetery on the east side of the city. Coffins were sealed. Families were told the bodies could not be viewed and the funerals were attended by officials. Some relatives were told the cause of death on the certificate was pneumonia. Others were told sepsis.

The story reached the West the following year through émigré reports, and American and British intelligence read it as an accident at a biological weapons plant. The Soviet government's answer was the meat. In 1988, a Soviet delegation traveled to the United States and presented the case in detail to American scientists, with clinical descriptions and figures, arguing that the outbreak was gastrointestinal and had come from animals slaughtered in the villages. The presentation was thorough. Among those who reviewed it was Matthew Meselson, a Harvard molecular biologist who had spent years working on chemical and biological weapons questions, and his assessment was that the account could not be disproved with what was available.

In 1992, Boris Yeltsin stated that the outbreak had been caused by the military. That opened the city. Meselson, the anthropologist Jeanne Guillemin, and a small team went to Yekaterinburg, which was the name the city had gone back to, and did the work that had not been possible before. They found families. They asked one question above all others: where was this person on April 2, 1979? Then they put every answer on a map of the city.

The dots fell into a narrow band. It ran from Compound 19 to the south-southeast, through the ceramics factory, through the pipe plant, out through the residential blocks, and past the city limit. Livestock had died in villages strung along the extension of the same line. Meteorological records for that day gave a wind from the north-northwest. The team published the reconstruction in the journal Science in 1994.

Grinberg and Abramova brought out what she had kept. The tissue was still good. It confirmed inhalational anthrax in the dead, and later genetic work on the material identified more than one strain in the samples.

No one was prosecuted. No Soviet or Russian official was charged in connection with the release or with the account given afterward. The program itself was not shut down in 1979 or in the years that followed. It grew through the 1980s across a network of institutes, and it was Yeltsin who ordered offensive work ended in 1992.

The figure most often used is sixty-six deaths, from the cases the 1994 study was able to document. Soviet records that surfaced later put it at sixty-four. Neither number accounts for people who may have been outside the study's reach, and no full list exists.

Compound 19 remained a closed military site after the Soviet Union ended. The ceramics factory across the road kept operating. The families who lost men in April 1979 put up a memorial in the section of the cemetery where the sealed coffins went, and the dates cut into the stones there run across a few weeks of one spring.

The evidence that it had never been the meat sat in a jar on a shelf in the same city, thirteen years, waiting for someone to be allowed to ask.