Both Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) in collaboration with local and state officials have been investigating the source of the contamination for the outbreak.

But the chances for the agencies to locate the source are slim although health officials still strongly believe that eating tainted raw Roma, plum or big round tomatoes is the cause for the outbreak.

On Friday, David Acheson, a top food safety official with the FDA suggested the source may remain forever a mystery because of the way the industry handles tomatoes.

Acheson was cited by Los Angeles Times as saying that possibly 90 percent of tomatoes at distribution centers might be repacked, a practice that makes it virtually impossible to trace the source.

"We continue to see a strong association with tomatoes, but we are keeping an open mind about other ingredients," said Patricia Griffin, a top epidemiologist with the CDC, quoted by Washington Post.

The CDC updated the outbreak on June 27 saying that a total of 810 people in 36 states and the District have fallen ill since Mid-April from the strain called salmonella saintpaul. And the last reported illness began June 15.

But officials said the data should be interpreted with caution.   The increased number may likely suggest that more people have become aware of the outbreak and reported their illnesses.

Roma, plum and big round tomatoes have a history of causing salmonella outbreaks. Tomatoes from green houses and other types of tomatoes, which are often sold locally, are seldom implicated in any outbreak.

The FDA has suggested that tomatoes regardless of their types from certain countries and states are safe to eat. Tomatoes with the vine attached are also safe to eat.

A health observer affiliated with foodconsumer.org warned that consumers should not over-react to the outbreak.    It is impossible for the industry to completely eliminate salmonella and other pathogens without causing huge damage to the nutrition value of a produce.   This is a fact that can’t be changed in the near future.

To avoid becoming ill from eating tomatoes, consumers should try to purchase and use only fresh tomatoes locally produced with the skin intact or even better with the vine attached. If possible, eat only cooked tomatoes.   After all, some nutrients in cooked tomatoes are easier to be absorbed.

Those who have some health condition that has compromised your immune system, however, should avoid eating raw tomatoes including products containing fresh tomatoes at restaurants.  Do not eat unhealthy tomatoes – those with the skin injured or rotten – at home or restaurant.