In October 1979, a West German newspaper run by Soviet émigrés ran a vague story alleging that an explosion in a military factory in Sverdlovsk (now Yekaterinburg) had released deadly bacteria, killing as many as a thousand. The story swiftly drew attention from other Western newspapers and eventually the U.S. government, because if Soviet factories were producing biological weapons, they were doing so in contravention of the 1972 Biological Weapons Convention.

Not so, Moscow swiftly retorted. Yes, an outbreak had killed dozens in Sverdlovsk, a closed city devoted to the Soviet military-industrial complex and the fourth largest in Russia today. But the culprit was tainted meat afflicted by anthrax.

Anthrax is an infection caused by a naturally occurring bacteria transported via spores that can be found all over the planet, and that can lie dormant in the soil for some time. Humans are most commonly affected by anthrax when abraded skin makes contact while handling an affected animal, particularly sheep or cattle, or animal products such as hides or wool. This form, known as cutaneous anthrax, leaves nasty sores, but is only fatal 20 percent of the time when left untreated. Much rarer gastrointestinal anthrax infections can result from eating infected animals.

However, the deadliest form of transmission involves breathing in anthrax spores, and has an 85 percent fatality rate. For pulmonary anthrax infections to occur, high concentrations of spores must be inhaled, and the spores cannot be too large, so as to slip past human mucous membranes. Once inside the human body, the bacteria multiply and in a couple of days begin producing deadly toxins. The victim may feel flu-like symptoms such as a sore throat and aching muscles, as well as shortness of breath and nausea. These symptoms progress to intense bleeding coughs, fevers, interrupted breathing and lethal meningitis (inflammation of the brain), leading to characteristic dark swelling along the chest and neck. Vaccination with antibiotics is effective at preventing the infection, but is not effective once the infection sets in.

Because anthrax can be easily manufactured and remains stable for years, it also was ideal as a biological weapon—a fact that U.S. scientists were aware of due to the experience of their own biological-weapons program, which had been active since 1943. It ultimately mass-produced six major strains of deadly bioweapons, many of which were designed to be spread by air-dropped cluster bombs. However, President Richard Nixon brought an end to the program in 1969, and three years later most of the world’s nations signed onto the 1972 Biological Weapons Convention, banning not only the use, but the production and development, of biological weapons.

However, the convention lacked a formal compliance and monitoring mechanism. Furthermore, it does not ban research on how to defend against bioweapons—which explains why weapons-grade anthrax is stored in U.S. government laboratories, and was available for use in the infamous anthrax letters that were sent shortly after 9/11, likely by a disgruntled employee.

U.S. intelligence analysts were skeptical of the Soviet tainted-meat story—CIA agents had obtained scattered reports supporting the narrative that there had been a factory accident at the time of the outbreak. Furthermore, the deaths of Soviet citizens spanning over two months did not cohere with a tainted meat-supply problem, which could have been dealt with swiftly. The Reagan administration seized on the incident to lay into the Soviet Union for apparently contravening the bioweapons ban.

The Soviet press maintained that this just showed how Washington was ready to use any tragedy afflicting the Soviet people to its political advantage. Some U.S. scientists, such as renowned Harvard researcher Matthew Meselson, were also inclined to believe the Soviet explanation. In 1981, the United States had alleged that Communist forces in Asia made use of “Yellow Rain” mycotoxins in Asia—allegations that were widely discredited. When, in 1988, Soviet scientist Pyotr Burgasov flew to the United States and presented autopsy records and photos from the victims of the Sverdlovsk outbreak, many Western scientists were finally persuaded that the incident merely reflected an embarrassing slip-up of the Soviet medical system.

However, even that autopsy data suggested some curious anomalies, including evidence of swelling of the lungs corresponding to a pulmonary anthrax infection. Furthermore, why had the outbreak mostly affected adult males, and relatively few women or children? New rumors emerged that the Soviet Union had developed some form of disease tailored to kill military-age men.

The true situation would soon come to light in 1992, after the fall of the Soviet Union. The newly anointed Russian president, Boris Yeltsin, confided to President George H. W. Bush at a conference that U.S. allegations about the Soviet bioweapon were entirely true. Yeltsin, as it happened, had been the party boss in the Sverdlovsk during the outbreak, which he admitted was the result of the bioweapons accident.

Just a year after signing on to the 1972 bioweapons ban, the Soviet Union had actually expanded its bioweapons production via a massive new civilian program, known as Biopreparat, that employed fifty thousand personnel scattered across fifty-two separate facilities. Biopreparat had manufactured hundreds of tons of a dozen different biowarfare agents, designed to be spread by missiles or sprayed out of airplanes. And mishaps did occur—for example, in 1971, weaponized smallpox being tested on Vozrozhdeniya Island had infected a scientist on a passing ship, leading to three deaths.

The deputy director of Biopreparat, Kanatzhan Alibekov (now Ken Alibek), would later immigrate to the United States and give his account of the Sverdlovsk incident in his book Biohazard, based on accounts he overheard from several colleagues.

The bacteria had originated from a bioweapons facility in Sverdlovsk known as Compound 19A, built in 1946 “using specifications found in the Japanese germ warfare documents captured in Manchuria,” according to Alibekov. The Japanese Unit 731 was infamous during World War II for both testing and field deploying bioweapons targeting Chinese civilians.

Compound 19A produced tons of anthrax in powdered form annually, for release from ballistic missiles—in particular a strain known as Anthrax 836 selected (not designed) because it was particularly deadly to humans. One day—Alibek places the date as March 30, 1979, though most sources insist it was early April—a technician removed a clogged filter and left a note indicating it needed to be replaced.

His account continues:

Compound 19 was the Fifteenth Directorate's busiest production plant. Three shifts operated around the clock, manufacturing a dry anthrax weapon for the Soviet arsenal. It was stressful and dangerous work. The fermented anthrax cultures had to be separated from their liquid base and dried before they could be ground into a fine powder for use in an aerosol form, and there were always spores floating in the air. Workers were given regular vaccinations, but the large filters clamped over the exhaust pipes were all that stood between the anthrax dust and the outside world. After each shift, the big drying machines were shut down briefly for maintenance checks. A clogged air filter was not an unusual occurrence, but it had to be replaced immediately.

Lieutenant Colonel Nikolai Chernyshov, supervisor of the afternoon shift that day, was in as much of a hurry to get home as his workers. Under the army's rules, he should have recorded the information about the defective filter in the logbook for the next shift, but perhaps the importance of the technician's note didn't register in his mind, or perhaps he was simply overtired. When the night shift manager came on duty, he scanned the logbook. Finding nothing unusual, he gave the command to start the machines up again. A fine dust containing anthrax spores and chemical additives swept through the exhaust pipes into the night air.

The missing filter was noticed hours later and swiftly corrected—but by then it was too late. A brisk night breeze had carried the deadly spores over into an adjacent ceramics factory, infecting the largely male factory laborers working the night shift. Nearly all died within a week.

The city authorities were kept in the dark about the accident until the outbreak became apparent. Then the party swiftly engaged in a cover-up. Troops established a perimeter around the factory, while Soviet officials announced that tainted meat was responsible. Hundreds of stray dogs were shot and black-market food vendors were arrested for “spreading tainted food.” The KGB destroyed hospital records and pathological reports documenting the outbreak, while the victim’s bodies were bathed in chemical disinfectants to remove the evidence left by the spores.

According to Alibek, damage control measures instigated by ill-informed Soviet officials actually worsened the outbreak.

The local Communist Party boss, who was apparently told that there had been a leak of hazardous material from the plant, ordered city workers to scrub and trim trees, spray roads, and hose down roofs. This spread the spores further through "secondary aerosols"—spores that had settled after the initial release and were stirred up again by the cleanup blitz. Anthrax dust drifted through the city, and new victims arrived at the hospitals with black ulcerous swellings on their skin.

Through May, at least ninety-nine Soviet citizens were infected and sixty-four died within a two-and-a-half-mile radius of the factory. Alibek claims he was told the actual count was closer to 105. For sheep, which were more susceptible to the spores, cases were reported within thirty miles.