On Thursday, state officials warned consumers not to eat some jalapenos and avocados delivered to stores and restaurants throughout the state because they had been linked to salmonella.

The announcement was the latest in a string of highly publicized salmonella outbreaks tied to fresh produce, including the one initially linked to tomatoes earlier this summer.

But before officials were able to tell consumers where the tainted products were coming from, there was a long 10-day investigation.

When they started, all that investigators knew was that four people had gotten sick after eating at a Mexican restaurant in Charlotte.

Along with federal officials from the Centers for Disease Control, state workers began executing a "track back" -- an ever-tightening circle of interviews, testing and research until the source of the bacteria is discovered.

They started with the people who had eaten at Cantina 1511 between June 8 and 14.

Using credit card receipts, they located 45 patrons -- both sick and healthy -- and interviewed them about what they ate, even reading the menu back to them to help jog memories.

"The critical part of tracing back is interviewing the people who ate the food and having them remember," said Audrey Pilkington, quality systems manager for the N.C. Department of Agriculture and Consumer Services. "Without that, it's so much more of a needle in the haystack."

Then investigators talked with the restaurant's staff to determine what was in the food those people ate and then tested 22 ingredients from salt to cumin, said Joseph Reardon, director of the agriculture department's food and drug protection division. The next question -- where the restaurant got its products -- led them to El Campo Produce in Charlotte, where they compared the items they tested with shipping invoices for the restaurant's recent orders.

"We wanted to make sure we got 100 percent of the products," he said. "We focused on things that weren't in the restaurant."

They tested produce from dozens of pallets, as well as the distribution center's equipment and even the ice.

Two items -- jalapeno peppers and avocados -- came back positive for salmonella. They had come from a Texas supplier, Grande Produce Limited.

At the same time, Texas officials were doing their own testing and identified the same strain of salmonella leading back to the same company in Texas.

The state's announcement Thursday came on the same day that federal officials cleared tomatoes of being the cause of a salmonella outbreak earlier this summer and instead indicated that jalapeno and serrano peppers could be the source. North Carolina's investigators had found a different strain of salmonella than that which has sickened 1,100 people nationally this summer.

State officials continue to work with federal officials to find the outbreak of that salmonella scare.

"We have not found the smoking gun yet," said state epidemiologist Jeffry Engel.

In addition, they continue to try to find out how the produce at the El Campo distribution center came in contact with salmonella.

Salmonella can be transferred to produce through unsanitary handling, transportation vehicles or even in soil. Now inspectors are looking closely at the transportation methods used to move the affected produce.

In addition, state inspectors are still looking for other stores and restaurants that may have received shipments from Grande Produce Limited through a different distribution company.

Department of Agriculture and Consumer Services spokesman Brian Long predicted the list of affected stores and restaurants will grow beyond its current 130.

Only one of those, Taqueria Mi Pueblo at 223 The Village in Durham, is in the Triangle.

State inspectors will work into next week visiting all of those establishments to make sure the affected products have been removed.

"It's going to go into next week," he said.