But they could find no trace of the bacteria when they inspected the Golden Corral on Barrett Parkway on Aug. 21.
On Wednesday, as state and Cobb County health officials publicly discussed news of the outbreak for the first time, inspectors looked again at the restaurant where at least 17 victims had eaten.
"Something is going on we can't explain, and we have to find what it is," said Dr. Susan Lance-Parker, an epidemiologist with the state Division of Public Health.
Health officials believe up to 23 cases could be linked to the restaurant, but they have interviewed people in only 17 cases.
The restaurant closed voluntarily Tuesday night for the inspection and a thorough cleaning and disinfecting. It will remain closed today as inspectors continue their investigation.
"This the most devastating, shocking thing we've ever experienced," said Charles Winston, owner of 12 Golden Corral restaurants in metro Atlanta.
Symptoms days later
Salmonellosis -- marked by fever, abdominal cramps and diarrhea -- is caused by one of 2,000 strains of the bacteria salmonella.
Symptoms generally occur one to three days after exposure but can be delayed for as long as a week. Salmonellosis generally is not life-threatening but can be fatal in the elderly or people with depressed immune systems.
The illnesses in this outbreak, Lance-Parker said, were caused by salmonella berta, a particularly unusual strain.
"We see only five or six cases [involving salmonella berta] a year in Georgia," Lance-Parker said, adding that about 1,400 cases of salmonellosis are reported in Georgia each year.
Lance-Parker said a few salmonella berta cases were reported in June and about a dozen in late July, including the person who later died. The victim "had an underlying health condition" that contributed to the death, said Lance-Parker.
Citing their interpretation of federal privacy laws governing health care, state officials declined to reveal the names, ages or genders of the victims.
The steak and buffet restaurant scored a 79 of a possible 100 during an Aug. 21 health inspection, but Lance-Parker said the violations were mostly technical and nothing that would have contributed to the spread of the salmonella.
The restaurant scored a 99 on a follow-up inspection the next day. Its other scores in the past two years were no lower than 90 and more typically 98 or higher.
After the Aug. 22 follow-up inspection and no more reports of salmonella, public health officials figured the outbreak was a one-time event and the source of the bacteria, perhaps contaminated food, was gone.
But two new cases linked to the Golden Corral surfaced earlier this week, Lance-Parker said. One of the victims whose case came to the attention of authorities this week came down with symptoms three days after the Aug. 21 inspection.
On Wednesday, many diners planning on lunch at the Golden Corral had to find another place.
Marcos Lopez was dismayed. "It's our favorite restaurant," said Lopez, who is from Venezuela and has been with relatives in Acworth for a few weeks. "It's not very expensive and they have good food."
The majority of salmonella cases in the United States are caused by two types of the bacterium: salmonella serotype typhimurium and salmonella serotype enteritidis, according to the Centers for Disease Control and Prevention.
Identifying the berta strain as the culprit is surprising, said Michael Doyle, director for the Center for Food Safety at the University of Georgia and an internationally recognized expert on food-borne pathogens.
"This is not a common strain that are typically associated with food," said Doyle, who is not involved in the investigation.
"It could be the salad bar, it could have been meat or it could have been cross contamination or it could have been a food handler," he said.
Salmonella contamination typically gets noticed when groups of people become sick within days of each other.
Doyle said it seemed unusual for the outbreaks to span two months.
"You'd almost think there's something in the environment or a food that's stored a long time, or an ingredient, that's causing it to go on that long," he said.
Staff writers Jennifer Brett and Patricia Guthrie contributed to this article.