How did the biggest cluster in the US emerge in a corner of South Dakota? Infections spread like wildfire through a pork factory and questions remain about what the company did to protect staff.

On the afternoon of 25 March, Julia sat down at her laptop and logged into a phony Facebook account. She'd opened it in middle school, to surreptitiously monitor boys she had crushes on. But now, many years later, it was about to serve a much more serious purpose.

"Can you please look into Smithfield," she typed in a message to an account called Argus911, the Facebook-based tip line for the local newspaper, the Argus Leader. "They do have a positive [Covid-19] case and are planning to stay open." By "Smithfield", she was referring to the Smithfield Foods pork-processing plant located in her town of Sioux Falls, South Dakota. The factory - a massive, eight-story white box perched on the banks of the Big Sioux River - is the ninth-largest hog-processing facility in the US. When running at full capacity, it processes 19,500 freshly-slaughtered hogs per day, slicing, grinding and smoking them into millions of pounds of bacon, hot dogs and spiral-cut hams. With 3,700 workers, it is also the fourth-largest employer in the city.

"Thank you for the tip," the Argus911 account responded. "What job did the worker who tested positive have?"

"We are not exactly sure," Julia wrote back.

"OK, thanks," Argus911 replied. "We'll be in touch."

The next day, at 7:35am, the Argus Leader published the story on its website: "Smithfield Foods employee tests positive for coronavirus". The reporter confirmed through a company spokeswoman that, indeed, an employee had tested positive, was in a 14-day quarantine, and that his or her work area and other common spaces had been "thoroughly sanitised". But the plant, deemed part of a "critical infrastructure industry" by the Trump administration, would remain fully operational.

"Food is an essential part of all our lives, and our more than 40,000 US team members, thousands of American family farmers and our many other supply chain partners are a crucial part of our nation's response to Covid-19," Smithfield CEO Kenneth Sullivan said in an online video statement released 19 March to explain the decision to keep factories open. "We are taking the utmost precautions to ensure the health and well-being of our employees and consumers."

But Julia was alarmed.

"There had been rumours there were cases even before that," she recalled. "I heard about people getting hospitalised from Smithfield specifically. They only know from word of mouth."

Julia does not work at the factory. She is a graduate student in her 20s, stuck back at home after her university shut in response to the Covid-19 pandemic. Her parents, two long-time Smithfield employees with whom she is especially close, told her what was happening at the factory that day. She is just one of several adult children of factory workers - many the first-generation children of immigrants, some calling themselves Children of Smithfield - who have taken it upon themselves to speak out about the outbreak.

"My parents don't know English. They can't advocate for themselves," said Julia. "Someone has to talk for them."

Her family, like many others in Sioux Falls, did everything they could to avoid falling ill. Julia's parents used up all their remaining vacation time to stay home. After work, they took off their shoes outside and headed straight into the shower. Julia bought them cloth headbands at Walmart to pull over their mouths and noses while on the line.

For Julia, alerting the media was just the next logical step in trying to keep them all healthy, by creating public pressure to close the plant down and keep her parents home. Instead, it marked the beginning of nearly three anxiety-filled weeks during which her mother and father continued to report to a factory they knew could be contaminated, to jobs they could not afford to lose. They stood side-by-side less than a foot away from their colleagues on production lines, they passed in and out of crowded locker rooms, walkways and cafeterias.

During that time, the number of confirmed cases among Smithfield employees slowly mounted, from 80 to 190 to 238.

By 15 April, when Smithfield finally closed under pressure from the South Dakota governor's office, the plant had become the number one hotspot in the US, with a cluster of 644 confirmed cases among Smithfield employees and people who contracted it from them. In total, Smithfield-related infections account for 55% of the caseload in the state, which is far outpacing its far more populous Midwestern neighbour states in cases per capita. According to the New York Times, the Smithfield Foods case numbers have surpassed the USS Theodore Roosevelt naval ship and the Cook County Jail in Chicago, Illinois.

Those figures were released one day after the first Smithfield employee died in hospital.

"He got that virus there. He was very healthy before," his wife, Angelita, told the BBC in Spanish. "My husband will not be the only one to die."

The Smithfield pork plant, located in a Republican-led state that is one of five in the US that has not issued any kind of shelter-in-place order, has become a microcosm illustrating the socioeconomic disparities laid bare by the global pandemic. While many white-collar workers around the country are sheltering in place and working from home, food industry workers like the employees at Smithfield are deemed "essential" and must remain on the front lines.

"These jobs for essential workers are lower paying than the average job across America, in some cases by significant margins. So home health aides, cashiers - absolutely essential, on the front lines, have to physically report to work," said Adie Tomer, a fellow at the Brookings Institute. "They are more predominantly African American or Hispanic than the overall working populations."

The workforce at Smithfield is made up largely of immigrants and refugees from places like Burma, Ethiopia, Nepal, Congo and El Salvador. There are 80 different languages spoken in the plant. Estimates of the mean hourly wage range from $14-16 an hour. Those hours are long, the work is gruelling, and standing on a production line often means being less than a foot away from your co-workers on either side.

The BBC spoke to half a dozen current and former Smithfield employees who say that while they were afraid to continue going to work, deciding between employment and their health has been an impossible choice.

"I have a lot of bills. My baby's coming soon - I have to work," said one 25-year-old employee whose wife is eight months pregnant. "If I get a positive, I'm really worried I can't save my wife."

Food processing plants throughout the country are experiencing coronavirus outbreaks which have the potential to disrupt the country's food supply chain. A JBS meatpacking plant in Colorado has shut after five deaths and 103 infections among its employees. Two workers at a Tyson Foods plant in Iowa also died, while 148 others were sickened.

The closure of a large meat processing facility like the one in Sioux Falls causes massive upstream disruption, stranding farmers without a place to sell their livestock. About 550 independent farms send their pigs to the Sioux Falls plant.When announcing the shutdown, Smithfield CEO Sullivan warned of "severe, perhaps disastrous, repercussions" for the supply of meat.

But according to Smithfield employees, their union representatives, and advocates for the immigrant community in Sioux Falls, the outbreak that led to the plant closure was avoidable. They allege early requests for personal protective equipment were ignored, that sick workers were incentivised to continue working, and that information regarding the spread of the virus was kept from them, even when they were at risk of exposing family and the broader public.

"If the federal government wants the company to stay open, then whose responsibility is it to make sure these companies are doing what they have to do to keep them safe?" said Nancy Reynoza, founder of Que Pasa Sioux Falls, a Spanish-language news source who said she's been hearing from distraught Smithfield workers for weeks.

The BBC submitted a detailed list of questions and worker allegations to Smithfield, and they did not comment on the allegations put to them on individual cases.

"First and foremost, the health and safety of our employees and communities is our top priority each and every day," the statement said. "Beginning in February, we instituted a series of stringent and detailed processes and protocols in early March that follow the strict guidance of the Centers for Disease Control and Prevention (CDC) to effectively manage any potential Covid-19 cases in our operations."

The outbreak left people like Julia, whose mother has underlying, chronic health conditions, overwhelmed by the fear that her parents were putting their lives at risk in an attempt to keep their jobs.

"My parents are all I have. I have to think about potentially not having them in my life," she said, her voice breaking. "I want to share what's going on so there's an actual track record of what the company isn't doing."

Ahmed first saw Neela on the Smithfield floor during one of their shifts. He liked her skin, she liked his laugh. When he started asking around about her, Ahmed learned that they were both from the same village in Ethiopia and they both spoke the same language, Oromo.

"Wow, I'm so excited. In my breaktime, I keep searching where she work," Ahmed recalled. "Right away, I stop by her line. I say, 'Hey, what's up.' I tell her she's beautiful."

Ahmed took Neela to a trendy New American restaurant. They went on a week-long vacation to Wisconsin Dells, a campy Midwest vacation destination known for its water slides and hot springs. They fell in love and got married.

Now Neela is eight months pregnant with their first child. Although she quit Smithfield back in December, Ahmed continued going to work during the outbreak even though he was terrified that he would infect his wife and their unborn baby with the virus. Because Neela started having difficulty walking in her third trimester, Ahmed needed to help her - they can't isolate from one another.

Ahmed says two of his friends in the plant have tested positive. Then he began exhibiting symptoms himself.

"Smithfield - they don't care about employees," said Neela. "They only care about their money."

According to Kooper Caraway, president of the Sioux Falls AFL-CIO, union officials approached management at Smithfield in early March to request multiple measures to increase worker safety, including staggering shifts and lunch schedules, which can pack 500 workers into the factory cafeteria at once. He said they also requested personal protective gear like masks and overcoats, temperature-checking at the doors and sanitation stations.

"This was before anyone at the plant tested positive," said Caraway. "Management dragged their feet, didn't take worker demands seriously."

Tim was a new employee going through orientation when he heard about the first case from someone sitting next to him. But he says after that initial announcement, the company got very quiet.

"We didn't really hear nothing more about the coronavirus outbreak," he said. "We thought it was good." Then, on 8 April, the South Dakota State Health Department confirmed there were 80 cases at the plant. Multiple employees told the BBC that they found out from media reports, not from management at Smithfield.

"I've found out about some people having the virus in my department, but other co-workers told me," said Julia's mother, Helen.

A temperature checking station was erected under a white tent at the main entrance to the factory, but Reynoza and Caraway both said that they were told workers with running elevated temperatures were allowed to come into the factory anyway. According to Helen, if workers wanted to avoid the temperature check, they could enter a side door.

Smithfield instituted other changes, like building cardboard cubicles around lunch table seats to create a barrier between workers, staggering shifts, and putting out hand sanitiser stations. But multiple workers said - and photos sent to the BBC seem to confirm - that personal protective equipment came in the form of beard nets to wear over their faces, which do not protect from airborne particles like a surgical or N95 mask would.

"I haven't read anything from the CDC that says a hair net over your face will do much good," said Caraway.

Smithfield did not respond to questions about the beard nets or provide details about what PPE they made available to workers, writing instead that, "given the stress on supply chains, we have been working around the clock to procure thermal scanning equipment and masks, both of which are in short supply".

At a JBS Plant in Worthington, Minnesota, 30 minutes away from Sioux Falls, union representatives said their company provided workers with "gloves, surgical masks, face shields, overcoats", according to the Star Tribune. They have not had a case yet. A spokesman for Tyson Foods told the New York Times that their policy is to notify employees if they have been in contact with anyone who is confirmed to have the virus.

In response, some employees started bringing their own masks to the plant. Others began quarantining themselves from family.

Kaleb, who has been with Smithfield for 12 years, told the BBC that for the past two weeks, he's been sealing himself in a room away from his wife, his six-month-old daughter and his three-year-old son because he can't be sure he isn't bringing the virus home with him everyday.

"My little boy you know, I lock the door - he knock on the door. 'Hey, daddy you wanna come out?' I say, 'Go with your mom,'" he says. "I don't have a choice. What can I do? I want to try to save my family."

If employees like Kaleb were to quit, they would be ineligible for unemployment. Advocates are hearing from visa-holders who fret that even if they were to apply for unemployment, they might be considered "public charges" which could render them ineligible for permanent residency under a new rule enacted by the Trump administration last year. The Coronavirus Aid, Relief, and Economic Security (Cares) Act excludes anyone living in a mixed-status household with an undocumented family member.

"They do not qualify for anything," said Taneeza Islam, the executive director of South Dakota Voices for Peace and an immigration lawyer. "Their choice is between putting food on the table, and going to work and getting exposed."

On 9 April, with 80 cases confirmed, Smithfield released a statement saying that the plant would close for three days over the Easter weekend for deep cleaning, and return to full capacity that Tuesday. "The company will suspend operations in a large section of the plant on April 11 and completely shutter on April 12 and April 13," a statement from the company read.

But the BBC learned through interviews with workers and advocates that Smithfield employees were still being called into work on all three days. Reynoza took videos showing the company parking lot filled with cars, and employees entering the plant. Caraway said he learned subsequently that the plant was running at about 60-65% capacity, meaning hundreds of workers were still coming in.

"I haven't stopped working yet. I worked Friday, Saturday, Sunday and they want me to come back today," Tim told the BBC on the Monday after Easter weekend. "I'm terrified. Terrified. Like I'm at a loss for words. [But] I got four kids to take care of. That income is what provides a roof over my head."

Sioux Falls Mayor Paul TenHaken, who said he was impressed and satisfied by the mitigation efforts taking place at Smithfield, admitted he felt surprised when he learned that the plant was still partially open.

"There could have been more transparency by them on the measures they were taking," he said. "The message to the public didn't match the actual plan."

Smithfield began offering employees a $500 "responsibility bonus" if they finished their shifts through the end of the month, which Islam characterised as a "bribe" to work in unsafe conditions.

Sara Telahun Birhe, an organiser with Children of Smithfield, said her mother had previously decided she would not return, but changed her mind when she heard about the bonus. "We're devastated by the idea that she's going to go in just for $500," Telahun Birhe said.

In its statement, Smithfield wrote that the bonus is part of Smithfield's #ThankAFoodWorker initiative, adding: "Employees who miss work due to Covid-19 exposure or diagnosis will receive the Responsibility Bonus."

In part due to the incomplete shutdown and in part due to the rising number of cases coming out of the plant, on 11 April both South Dakota Governor Kristi Noem and TenHaken sent a joint letter to Smithfield calling for a 14-day "pause" in operations. The next day, Smithfield leadership announced that they would comply - on 15 April, meaning there was still one more day of work in a building.

Caraway said workers who went in on the final Tuesday received roughly double their normal wages but there had been no deep clean. "They're still going into a dirty building."

Smithfield did not respond to questions about when its Sioux Falls factory underwent deep cleaning, writing that "our facilities are thoroughly cleaned and sanitized every single day".

Both of Julia's parents were scheduled to work at Smithfield on Tuesday 14 April, its final day in business before the 14-day shutdown. Then, on Saturday, Helen started to cough. The next day, as fluffy white snow flew over Sioux Falls, Julia insisted that her mother get tested. Helen tried to put it off, saying it was nothing.

"My mom just really hates going to the doctor," said Julia, who eventually won the argument and Helen went to a drive-in testing centre at the local hospital. They stuck a swab into the back of each nostril and sent her home.

"If I were to have Covid-19, I clearly would have gotten it at the factory," she said. "This week I have worked on three different floors. I've eaten in two different cafeterias. Just imagine every place I've been in, touched inside that factory. I've been walking through the whole place."

On the Tuesday they were scheduled to return to work, Julia's parents woke up at 4am like they normally do and called into Smithfield to explain that they couldn't come while awaiting Helen's test result.

The call finally came later that afternoon.

Julia spoke to the medical technician on her mother's mobile phone, while her parents sat watching her face for a reaction. When Julia heard the words "positive for Covid-19" she gave them a thumbs up, which she meant to indicate "positive". Helen and Juan misunderstood, and reached out for one another, a gesture of celebration that horrified Julia as she scrambled to explain that, no, Helen does have the virus. Her father retreated into the kitchen, where Julia glimpsed him trying to hold back tears.

On the same day that Helen received her results, the issue of the Smithfield plant had turned fully political. Mayor TenHaken formally requested that Governor Noem issue a shelter-in-place order for Sioux Falls' surrounding counties as well as an isolation centre. She denied both requests. Despite the steep increase in cases, Noem also continued to decline to issue a shelter-in-place order in South Dakota, specifically saying that such an order would not have prevented the Smithfield outbreak.

"That is absolutely false," she said.

Instead, she approved the first state test of hydroxychloroquine, a drug that President Donald Trump has frequently cited as a possible treatment for coronavirus.

It was also the same day that Agustin Rodriguez Martinez, a quiet, deeply religious man originally from El Salvador, died from the illness, alone in hospital. He was 64, the first known death connected to the outbreak at Smithfield Foods. Reynoza, a friend of his for the past decade, said that he rarely complained about his gruelling job sawing the legs off pig carcasses and that he doted on his wife Angelita, whom he knew for only a month before they married. They were together for 24 years.

"He was her prince."

Angelita says she noticed something was off when her husband started coming home with the lunch she had packed him untouched. He began experiencing symptoms on 1 April, seven days after the first case of coronavirus was reported publicly at the factory. First there were the headaches, then aches and chills. Next came the shortness of breath. According to Angelita, on his final day of work at the factory, he was mopping the floors with a fever.

By that Sunday, he could no longer breathe.

Angelita brought him to hospital, but was not allowed to go with him. She learned through her pastor that he was put on a ventilator almost immediately. He was on it for 10 days before he died on 14 April. "I took him to the hospital and left with nothing," she said. "Now I have nothing."

Alongside her grief, Angelita is also angry at Smithfield Food for not closing the factory earlier. "They care more about their money than our lives," she said in tears. "The owners don't care about our pain. Mothers are crying for their children. Wives are crying for their husbands. There are so many cases of the virus there."

The 73-year-old widow also shared that she has developed a cough.

Two days after her mother's positive coronavirus diagnosis, Julia woke up on the couch with a headache, a cough and a dry throat. For the first time since the pandemic arrived in her life, she had slept through the night but awoke feeling more exhausted than ever.

After calling the Covid hotline and informing them she was the daughter of a Smithfield worker, Julia pulled on her faux fur-trimmed parka, disinfected the steering wheel and gear shift in her mom's car, and set out towards the drive-thru testing site.

She was in relatively good spirits, despite the fact that almost everything she had attempted to prevent when she tipped off the local newspaper nearly a month ago had come to pass. The factory had remained open. Her mother had the virus and her father was exposed. Her city had become the epicentre of the pandemic in the state of South Dakota. People died.

And now, she might be sick, too.

"I just wanna cry," she said, as she steered towards the hospital.

All over the city, Smithfield workers and their families were going through a similar experience. The same day Julia's mother got her diagnosis, Sara Telahun Birhe was relieved to find out that her mother's Covid-19 test was negative. Neela and Ahmed got the call that he was infected, and the couple sealed themselves away from one another in separate bedrooms. They communicate via text. She makes him ginger tea and leaves it for him on the counter. He obsessively disinfects everything he touches.

Tim said he worked his final shift at Smithfield while experiencing symptoms on Tuesday 14 April, and went in for a test the following day. He is still awaiting results. He said 20 people on his crew have tested positive.

At about the same time that Julia set off to get her test, officials from the Centers for Disease Control and Prevention were entering the Smithfield plant, along with representatives for the state and local health departments. According to the South Dakota governor's office, CDC officials were flown in from Washington DC to "assess" what it would take to safely reopen the plant. Meanwhile, Smithfield announced the closure of two more of its facilities in Missouri and Wisconsin, where "a small number of employees… have tested positive for Covid-19".

Although she arrived just 20 minutes after the testing site opened, Julia was greeted by a line of 15 cars ahead of her. "I hate waiting in line," she muttered, sipping from her water bottle, every now and then emitting a soft cough.

After 30 minutes, she pulled up to what looked like a huge garage and a sign that instructed, "have ID and insurance card ready".

"OK, now I'm anxious," she said. "I don't want to do this."

She and the car ahead of her pulled into the bay, and a healthcare worker in a full protective suit, mask, gloves and face shield plunged a long swab into Julia's right nostril and then her left. She grimaced and shuddered.

"Do you need a Kleenex?" the tester asked. "Yes, please," said Julia.

With instructions to "go home, stay home, don't go anywhere," the bay doors opened and Julia pulled back out into the sunlight. "That was so uncomfortable that I actually am crying," she said, pulling into a parking spot to collect herself.

Julia sat at the steering wheel watching cars go in and out of the parking lot. She lamented the fact that now their household had a new potential infection, the clock on their quarantine had to restart. "I just want to go to TJ Maxx," she said, smiling.

After a few minutes, it was time to turn towards home, her parents, and the house Helen and Juan worked so many hours in the plant in order to afford, where they would all quarantine together for at least the next 14 days.

"Now it's just a waiting game," said Julia. "I guess I can't get too in my head about it. But I will."

She should have her results in five days.

Names have been changed. BBC