MOSCOW: Natalya Konkova got a call from her 5-year-old son's day care centre at School No. 1357, asking her to pick up Yaroslav because he was running a fever and having trouble walking.

He got worse over the next 24 hours, with severe diarrhoea and vomiting, before an ambulance took him to a hospital. He was eventually diagnosed with dysentery.

"I've never seen anything like this before. It was scary," Konkova recalls.

Yaroslav was one of 127 children aged 3 to 7 who were diagnosed with dysentery after eating food at seven state-run day care centres and kindergartens in Moscow in mid-December.

While reports of dysentery are not new in Russia, they mostly have struck provincial areas far from the capital and in much smaller outbreaks. Even more unusual is that the catering firm blamed by opposition activists for the outbreak at six of the seven Moscow sites is owned by businessman Yevgeny Prigozhin, a close ally of President Vladimir Putin.

Prigozhin, who has won $2 billion in contracts for supplying food to Moscow schools since 2009, built an empire on catering and maintenance contracts for the army and has been nicknamed "Putin's chef" for serving Kremlin functions. He also has been reported to run a private military company known as Wagner that sends Russian contractors to Syria and other countries.

The magnate was among the Russians indicted last year by a US grand jury in the investigation by special counsel Robert Mueller, alleging he funded the internet trolls involved in interfering with the US presidential election in 2016. The US also imposed sanctions on Prigozhin and two of his companies, Concord Catering and Concord Management and Consulting. Prigozhin has denied any involvement, and Putin said last year that while he knew the businessman, he "doesn't count him" among his friends.

Prigozhin's company has denied it is to blame for the dysentery outbreak. The cases have caused an outcry, thanks to a lawyer who has turned a spotlight on the caterers and has mounted a campaign to help the parents whose children fell ill.

Lyubov Sobol, who works for the investigative team of anti-corruption campaigner and opposition leader Alexei Navalny, documented Prigozhin's rise from ex-convict in St Petersburg to Putin's Kremlin circle. She has taken up the case on behalf of the parents of the stricken children.

She also has a personal interest in sanitary conditions at the schools, since her 5-year-old daughter attends a Moscow day care centre, although not one of those that were affected.

Inna Chepeleva, whose daughter attended day care at School No. 1357 and came down with pneumonia attributed to the dysentery outbreak, said she was shocked at the refusal of officials there to explain what happened.

"Something was going on, but we knew nothing," she said.

Even though 11 children at day care at School No. 1357 had symptoms consistent with dysentery, the day care centre wasn't shut down for a quarantine for nearly three days.

A month after Sobol began a campaign on the outbreak, which included a YouTube video that got more than 300,000 views, Russia's chief investigative body launched a criminal inquiry into conditions at the day care centres.

Separately, parents of 27 children filed a lawsuit against Moscow authorities and Concord Ready-Meals Factory. The trial was supposed to start in April but the court has suspended hearings for at least two months pending the official probe. Another group of parents filed a similar lawsuit last month.

The Federal Consumer Oversight Agency confirmed 127 cases of dysentery. At public hearings in March, the capital's chief sanitary official, Yelena Andreyeva, denied early reports that blamed it on cottage cheese supplied by a company from southern Russia. Health and education officials would not say whether the outbreak would make them reconsider signing new contracts with Concord.

Six companies that are either directly owned by Prigozhin or affiliated with him have controlled almost all school and kindergarten catering in Moscow since 2011, providing prepared meals that can be reheated at school kitchens, according to public filings and the Spark-Interfax database.

His companies also have other lucrative deals to cater to state-owned hospitals and clinics in Moscow and the region.

Prigozhin and his representatives have rarely spoken to the media, but they invited the parents of two stricken children to tour one of their facilities. He also offered to pay compensation to the affected families as "financial aid," Concord's press office said, although his company denies it is to blame for the outbreak.

Concord representative Yuri Ostyuk told The Associated Press that "it's too early to talk about responsibility because the investigation is ongoing," adding that the company has implemented measures, including more lab tests, to ensure food quality.

In a written reply to Sobol's complaint, the Consumer Oversight Agency said numerous inspections at Concord Ready-Meals Factory as well as other firms affiliated with Prigozhin found violations of "sanitary standards" and some of the food tests at its facilities and schools produced "unsatisfactory results." The agency did not elaborate, and Concord did not immediately comment.

Sobol alleges she has faced a smear campaign from Prigozhin-controlled media, most recently when the Federal News Agency, or FAN in Russian, reported she does not have a university degree, while she says she graduated from a top law school with honours.

Anti-corruption campaigners like Sobol and Navalny have also complained of harassment from unidentified individuals. Both of them have worked on high-profile corruption investigations involving Russia's political and business elite.

When asked about reports of harassment and intimidation, Concord told the AP it was unaware of any, adding that Sobol has a "bad reputation in Russia."

Two employees of two school catering companies linked to Prigozhin — Moskovsky Shkolnik and Shkolnik-UZ — have cited lax sanitary standards and poor quality of food. The dysentery outbreak did not affect schools served by those two companies.

Natalya Shilova, a former manager at Moskovsky Shkolnik, said in an interview broadcast in March that staff ignored food safety standards when she worked there in 2017. Her son was among the children diagnosed with dysentery and was hospitalised for months for complications from the illness.

Moskovsky Shkolnik filed a defamation lawsuit last month against Shilova, as well as Sobol, Navalny and his anti-corruption foundation that released the video interview.

Fyodor Mishenev, who worked in two management positions at Shkolnik-UZ between 2016 and 2018, documented sanitary problems, posting photos on Instagram of rotten apples, oranges with worms and kitchen staff smoking on the premises. He said some staff at Shkolnik-UZ had to buy their own gloves and detergent because of a lack of supplies, adding that he and his colleagues often scrubbed kitchens before state sanitary inspections.

Representatives of Shkolnik-UZ could not be reached for comment, and Concord has denied any connection to the other firms supplying catering to Moscow schools and kindergartens, including Moskovsky Shkolnik and Shkolnik-UZ. Filings show that Prigozhin's Concord Ready Meals and the other companies that supply catering to Moscow schools have listed the same phone number, share registration addresses or have had the same management.

In making his accusations, Mishenev also said that the schools and parents bore some responsibility for making sure that authorities adhere to sanitary standards.

"I don't want to blame it all on Prigozhin or the government," he says. "It's our fault. We are not controlling them properly."

Young Yaroslav has developed pancreatitis, must take medication daily and has been advised to stay home because his immune system is too weak. His mother has had to quit her clerical job to care for him.

He misses his friends, he said as he played with his favorite toy, a rubber scorpion, but does not want to go back to the school.

"I'm scared," Yaroslav said.