The biggest foodborne illness outbreak in 10 years began on April 16, 2008, but no one knew it.
The evidence of the outbreak began surfacing on May 22, when the New Mexico Department of Health reported four confirmed cases of a specific type of Salmonella and 15 more cases caused by an unidentified Salmonella strain to the Centers for Disease Control.
By the end of the summer, 43 states, Washington D.C. and Canada had reported a total of 1442 cases.
"Tracking down causes of outbreaks is a huge challenge," said Thomas Kensler, a professor of toxicology in the Bloomberg School of Public Health. "The government, CDC in particular, did a pretty good job honing into what was going on."
Salmonella, a bacterium that causes fever, diarrhea, abdominal pain and sometimes vomiting, infects humans through consumption of contaminated food - usually animal products. However, vegetables can also cause human infection if they become contaminated through tainted manure or water.
Symptoms of Salmonella infection take between 12 and 72 hours to appear, and typically last from four to seven days.
Salmonella exists in many unique strains. The strain that caused this particular outbreak, Salmonella Saintpaul, is relatively rare.
However, the "vector" of the bacteria - the carrier - was a food that is commonly eaten across America and especially in the Southwest, the region that had the highest number of Salmonella cases. The main cause, which remained unknown until early July, was raw jalapeño peppers, which is an ingredient in salsa.
Other foods, most notably certain types of tomatoes, took the blame and the economic hit until the authorities were able to pin down the elusive jalapeño as the true guilty party.
Even after tomatoes were taken off the blacklist, some doubt remained as to whether they were involved in the outbreak. The CDC suspects that while jalapeño peppers caused most of the illness, serrano peppers and some tomatoes may also have been complicit.
Last June 3, the FDA warned residents of New Mexico and Texas not to eat red Roma, red plum or red round tomatoes, and on June 7 the rest of the nation was warned to avoid these foods as well. By June 11, CDC was reporting progress on the tomato front, but only two weeks later, there were 277 Salmonella Saintpaul cases in 25 states.
On July 9, when the number of cases reached 1000, CDC announced a new suspect - jalapeño peppers.
Even though the correct source was identified, the battle wasn't over. Tracking these infected jalapeños back to the farm and packing plant was a difficult task because the peppers were grown in Mexico.
CDC eventually reported that they were able to track the peppers back to two farms in Tamaulipas, Mexico, which both had sent their peppers to the same packaging plant.
The sluggishness of the epidemiologic investigation and the missteps along the way prompted some criticism of the CDC. The situation also brought national attention to the inadequacy of the food industry's technology for tracking foods to their sources and keeping consumers safe.
CDC attempted to defend its efforts and those of local health departments by explaining the complexity of processes of investigating of the source of a foodborne illness outbreak.
The investigation depended in large part on the accuracy of the memories of infected individuals. Each individual's food consumption history provided a clue to the CDC about which food was the vector for the illnesses.
Unfortunately, the huge size and complexity of the multinational food packaging industry kept the CDC off the mark and the nation off tomatoes for more than a month.
"Is the system vulnerable? Absolutely," Kensler said. He added, "As somebody who spends a lot of time overseas, especially in rural China, I feel so much better about our food safety than theirs."
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