When someone uses the phrase "biological attack" your mind doesn't immediately leap to hippy cults, but the biggest attack of this kind in US history was conducted by a free-love preaching sect.
In the 1970s, Bhagwan Shree Rajneesh became the leader of the (modestly named) Rajneeshees, in his home country of India. The cult's attitude towards sexuality (as well as a massive unpaid tax bill) put them at odds with the conservative (and tax-demanding) Indian government. So, in the early 1980s, a large group of the Rajneeshees fled to set up life in the US.
They settled on a 64,000-hectare ranch in central Oregon, planning to turn it into a bonafide city. The problem was that the leaders of the cult had failed to read the small print when purchasing their land. Though they owned the land, they couldn't just build whatever they wanted on it, nor move in as many people as they choose – they would need permission from the local authorities. This was a little bit of a problem, given that the leaders of the cult did not exactly mesh well with the locals.
When attempts at diplomacy with the local Wasco County authorities failed, they turned to more aggressive tactics to get their own way. Their first move involved overwhelming the vote in the nearby town of Antelope, which only had 50 residents. This allowed them powers such as being able to have their own police force – as well as some powers that were incredibly irritating to the local residents. They renamed the town "Rajneesh", for instance, while to the local recycling center they bestowed the moniker the "Adolf Hitler Recycling Center".
However, their numbers weren't enough to overwhelm the vote in the overall Wasco County, so their permission to expand was repeatedly denied. Leaders of the movement then decided to commit some voter fraud followed by biological warfare and a few murder attempts along the way.
First, they tried to rig votes by providing homeless people with shelter and food in return for voting for their chosen candidates. In order to keep them under control while staying on the ranch, there is evidence that the resident chemist drugged their beer with Haldol, an antipsychotic. The government caught onto the scheme and made a clause requiring at least 20 days of residency before voting. Naturally, after this plan failed, the cult's thoughts turned to suppressing the county vote by giving everybody synchronized diarrhea.
Now, there are a few major signs that your life has gone awry and you need to take a step back and reassess. If you own every Ed Sheeran album, for example, or if you have the phrase "Live Laugh Love" anywhere in your house. Another major red flag is when you have your own poison laboratory you've nicknamed the "Chinese Laundry" where you test out various poisons. This is what happened on the Rajneesh ranch, as the leaders cultivated pathogenic bacteria.
One early plan involved killing local beavers, crushing them down into a mulch, and then using said mulch to pollute the town's water supply. This was abandoned in favor of using Salmonella typhimurium, a strain of bacteria they figured would be much less likely to provoke investigation and suspicion.
First, they poisoned commissioners from Wasco County as they visited the ranch. Next, the cult carried out a rehearsal of the full-scale attack on voters, going out and contaminating salad bars in local restaurants with salmonella.
"During the first wave, eating either macaroni, potato, four-bean, or pea salads was associated with illness," they wrote in their report on the incident. "During the second wave, blue cheese dressing was associated with illness."
The investigation found that hygiene practices at the affected restaurants were not deficient – but it was years before they could tie the outbreak to the local sect.
In the meantime, the cult had moved on from merely trying to make a whole town poop and puke their way to election defeat, and had moved onto attempted assassination of officials.
The mass poisoning remains the biggest biological attack in US history with 751 victims, ranging from newborn to 87 years old, according to the Centers for Disease Control and Prevention.