I just ate a cantaloupe and I feel fine! For now...the recent outbreak of cases of listeriosis have prompted people to second-guess their choices in the grocery store and perhaps lean more toward canned or otherwise ultra-processed choices. But how do you know if what you just ate is OK? For starters, you can visit the FDA's website to check on specific product recalls on a continually updated basis. You would have to know the origin of that food product, and that means asking the grocery store where they get the items in question. But if you've already eaten a questionable item, what do you look for?
The symptoms of listeria monocytogenes infection (a type of bacteria) can take up to three weeks to appear after ingesting a contaminated food product, and the symptoms are just like the flu - fever, body aches, nausea, and diarrhea. Headache and neck stiffness are rarely associated with listeriosis and can indicate a severe infection resulting in meningitis. But the majority of people are minimally affected and do not seek any treatment because they just chalk it up to a random virus that runs its course over about a week. However, other people with certain health risks may not be so minimally affected.
Pregnant women are particularly at risk for problems with listeria infection, but not so much because it will affect their own body severely as much as the fact that the bacteria can cross the placenta to the baby's bloodstream. Preterm birth, miscarriage/stillbirth can result. Other at-risk groups include the elderly, the chronically debilitated, small children and those who have immune system deficiencies that don't allow them to fight bacterial infections.
Listeria infection is diagnosed mainly via clinical means - a physician identifies the signs within the context of a known outbreak. There is no rapid test available, and the bacteria must be cultured from blood or body fluids in order to be definitively identified. Once the outbreak is publicized in the news, people will begin to notice what they have been eating and pay attention to how they process the food in their own home.
Antibiotics are effective to treat listeria (penicillin and sulfa-based drugs will work), but again, these are only used in those with significant infection that lands them in the hospital with an intravenous line as opposed to just giving doses of oral antibiotics to people who THINK they might have been exposed.
As with any health issue, you will want to discuss any significant symptoms of possible listeriosis with your doctor such that prompt attention and treatment can be given if appropriate.