The current listeriosis outbreak has rattled the confidence of many consumers, now second-guessing what they may have dismissed as general nausea or the flu.

Anyone concerned he or she may have consumed a tainted product should be vigilant, and be on the lookout for the following symptoms of listeriosis:

• Vomiting
• Nausea
• Stomach cramps
• Diarrhea
• Severe headache
• Constipation
• Persistent fever
• Stiff neck
• Loss of balance
• Convulsions

Diagnosing listeria is performed through blood or spinal fluid tests. Symptoms may appear rapidly within hours or as late as 70 days after consuming a spoiled product.

For many patients, the disease can be treated with antibiotics. But for high-risk patients, including the elderly, pregnant women and people with compromised immune systems, the onset of the infection can be rapid.

Frances Clark, the first victim to be named in the Canadian outbreak, died at age 89. Clark, who had been living in a nursing home near Belleville, Ont., began experiencing symptoms on a Wednesday before dying the following Monday.

"By Saturday morning she was pretty well unconscious," said Clark's son, Tim Clark. "We didn't know if she knew us or not, her eyes would open and close but her breathing was very laboured, very raspy, very congested. The blood cultures finally started coming back and showing something by Saturday night, then on Sunday they had a confirmation that it was Listeria bacteria that was the culprit there."

Clark's daughter Karen said the onset was rapid.

"[She went] from a relatively healthy woman that's walking around with her walker to being within 48 hours of admission to death," she said. "It's overwhelming."

Health Canada advises patients that early diagnosis is crucial, particularly for people in high-risk groups. The federal department also notes no vaccine exists to treat listeriosis.