The risk of illness was "quite low," but anyone who ate raw food at the magazine's Feb. 14 party was urged to receive a preventive shot by Wednesday, the Los Angeles County Department of Public Health said.
According to media reports, singer-actress Beyonce Knowles, who graced this year's cover of the swimsuit issue, attended the party along with several high-profile models. Other guests included Guns N' Roses bassist Duff McKagan and Borat co-star Ken Davitian.
"The risk here is low," said Dr. Jonathan Fielding, the county director of public health. "Nonetheless, we felt it was appropriate to alert people."
Hepatitis A virus is spread from person to person by putting something in the mouth that has been contaminated, WebMD reports. Poor sanitary conditions and personal hygiene practices contribute to spread of the infection.
Most people don't require special treatment for hepatitis A, although according to WebMD, treatment can help with symptoms. It is not a chronic disease, and once you have gotten over a hepatitis A infection you can't get it again.
The virus is found in the feces of infected people. It attacks the liver and can cause fever, diarrhea and jaundice. It is rarely fatal.
The alert involves only 13 events, and medical authorities were paying particular attention to four catered events, including the SI party, the Los Angeles Times reported. The other three were not identified.
The affected employee was placed on medical leave, said Carl Schuster, president of Wolfgang Puck Catering.
"We immediately worked to take every precaution to further safeguard our patrons and other employees," Schuster said in a statement.
Sports Illustrated said in a statement that it was taking the situation very seriously and was working directly with county health authorities.
"We are alerting our guests and staff as quickly as possible to ensure they receive the relevant health warnings," the statement said.
Puck's restaurants and prepackaged foods were not affected, nor were any parties after Feb. 20, including Sunday's post-Oscars Governors Ball.