MADRID (Reuters) – Spain’s health ministry issued an international alert over the country’s biggest ever listeriosis outbreak on Wednesday as the number of people affected rose to 150, including one fatality.

Amid concerns over possible infection among the more than 80 million tourists who visit Spain annually, the ministry said it was checking another 523 suspected cases.

Most confirmed cases have been recorded in the southern region of Andalusia, where the packaged pork plant linked to the outbreak is situated. But there have been others as far away as Catalonia in the northeast and more around 50 people remain in hospital.

Listeria, the bacteria behind the infection, usually causes mild illness but can be dangerous to pregnant women, 23 of whom are among those still hospitalised, and those with weakened immune systems.

The ministry said it had issued alerts to EU authorities and the World Health Organization over the outbreak, which was on Tuesday confirmed to have killed a 90-year-old woman.

The plant in question, owned by Seville-based Magrudis, was inspected by health authorities after lab tests showed the presence of listeria in one of its products, the ministry said. All products manufactured in the plant since May 1 have been recalled.

The company has not responded to requests for comment.

“Obviously there was a failure to follow the established procedures,” acting health minister Maria Luisa Carcedo told reporters. “Now we need to carry out the inspections and investigations to figure out exactly where this failure took place.”

(Reporting by Ashifa Kassam, editing by Andrei Khalip and John Stonestreet)