A hepatitis A outbreak at a golf club in New Jersey has left nearly two dozen people very ill, according to health officials.

New Jersey Department of Health stated that 23 people have gotten sick so far, with one of them being “seriously ill.” They contracted hepatitis A from a food handler at the Mendham Golf & Tennis Club, and they were likely exposed between June 9 and June 30. However, they were not notified of possible exposure until July 5.

“The food handler was excluded from work and a review of other food handlers for vaccination and proof of immunity was conducted. Close contacts of the food handler were identified and given prophylaxis (vaccine or medication to prevent illness after exposure),” the New Jersey Department Of Health said in a statement.

When members were notified, they were told to also notify any guests who may have eaten with them at the club.

“This notification also advised that those who dined at the club when the food-handler was potentially infectious should receive post-exposure prophylaxis,” health officials added.

This “highly contagious” liver infection is caused by the Hepatitis A virus, and the health agency said it spreads when a person eats or drinks something “contaminated by small, undetected amounts of stool from an infected person.” The CDC states that those who contract hepatitis A are typically sick for “several weeks,” but they eventually often recover. While it is rare to die from hepatitis A, it can cause liver failure and death, typically in those who are 50 years of age or older. Symptoms of hepatitis A include fever, fatigue, dark urine, vomiting, joint pain, and jaundice, among other signs.