In mid-December, 20 employees of a capital investment firm in San Francisco all began experiencing stomach cramps and vomiting within a day or two of attending a private company party. It didn’t take any degrees in epidemiology for the group to trace their illnesses back to Delfina, the Italian restaurant that hosted the event and the one place where each individual had eaten in the past few days.

More than anyone else in San Francisco, Dr. Rajiv Bhatia is probably the first person who should know of a foodborne illness incident of that size. Bhatia is a professor of clinical medicine at University of California San Francisco and the director of occupational and environmental health for the San Francisco Department of Public Health, where he oversees illness outbreak investigations for the city.

But after the investment firm informed the restaurant that its food had sickened 20 out of 50 guests, neither the restaurant, the firm, nor any of the individuals notified the health department. Bhatia didn’t hear about the illnesses until December 29, when journalist Scott James called the health department asking about the incident.

James broke the story for the Bay Citizen and the New York Times, writing that the incident “highlights the absence of laws requiring restaurants to report illnesses.”

During his 13 years in public health, Bhatia said he has never seen an outbreak of this size go unreported by the victims, the restaurant or any medical professionals. He said the health department did not yet know if any of the victims sought medical attention.

In most states, lab-confirmed infections with Salmonella, Shigella, Listeria, E. coli O157:H7 and Hepatitis A are reportable, meaning that medical professionals report to state health departments, which in turn report to the federal Centers for Disease Control and Prevention.

However, the CDC urges that even suspected outbreaks of foodborne illness, or individual illnesses suspected to be foodborne, should also be reported.

California state law requires restaurants to report employee illnesses, but not customer illnesses, to the health department. In this case, the investment firm issued a report to Delfina detailing what each victim ate, and through a process of elimination the restaurant narrowed the possible sources down to three vegetable/leafy green items. Delfina then contacted its suppliers, but the restaurant still did not inform the health department.

“Whether we have to change the law or not, I think it’s in the interest of the food industry and food safety for restaurants to report illnesses to us,” Bhatia told Food Safety News. “I’m glad the restaurant did their investigation, but they don’t have the same tools we do to complete a thorough investigation.”

Bhatia said the health department’s investigation is still ongoing and they have not pinpointed a definite source or pathogen. Completing the formal investigation — which involves interviewing each of the 20 victims — may take a month or longer.

Some states, such as Washington, do require restaurants to report to health officials when their customers get sick. Dr. Jeff Duchin, University of Washington epidemiology professor and chief of communicable disease control for King County Public Health, told Food Safety News he could not imagine a reason why a restaurant shouldn’t report illnesses to their health department.

“The restaurant may feel that they understand what’s going on and that the situation doesn’t pose any risk outside that meal, but they have no way of actually knowing that,” Duchin said. “The public health people are experts in epidemiology. It could be that the contaminated product went to other places or was being sold in stores and the restaurant would not be equipped to trace that.”

Duchin also mentioned the outside chances that a restaurant employee could intentionally contaminate the food or that illnesses could involve an unusual pathogen the restaurant would not know to look for. Regardless of the cause, he reiterated that health officials are the best prepared to investigate these possibilities.

“A small cluster could be a manifestation of a very large problem,” Duchin said. “The sooner that’s recognized by the health department, the sooner the investigation can get under way to determine the source.”

Bhatia said that the San Francisco Department of Public Health receives between 400 and 500 foodborne illness reports every year, mainly from restaurant customers. The department launches an investigation whenever multiple complaints converge around a single establishment, but they have no way of knowing how many illnesses fly under their radar.

Despite the lack of laws on restaurants reporting illnesses in California, Bhatia said he thinks anyone serving food to the public should feel obligated to report them to health officials. 

“I think it should be mandated not only for restaurants but for business cafeterias, schools or anywhere else that serves food to the public,” Bhatia said. “We want to have redundant sources of information pointing to the same place.”

On Monday, Delfina posted a statement to its website concerning the incident, calling it an isolated case and reassuring customers that the restaurant is working with the health department.