Escherichia coli (E. coli)

I’m sure many of you have recently seen reports in newspapers or on TV about certain pre-packaged, ready-to-eat vegetables being contaminated with E. coli. Public health authorities may warn the public not to purchase or consume affected products.

In fact, there have been numerous warnings—both major and minor—regarding E. coli contamination in drinking water and food over the past 30 years. However, the total of more than 100,000 reported cases cannot be verified without a specific geographical area, time period, and source. Among these incidents, the outbreak that occurred in May 2000 in Walkerton, Ontario—a town with a population of approximately 5,000—where E. coli and Campylobacter contaminated the water supply, resulting in seven deaths and thousands of people becoming ill, garnered significant attention.

E. coli is a bacterium commonly found in the intestines of humans and other warm-blooded animals. Most strains are harmless, but certain strains can cause serious illness. The bacteria can spread through animal or human feces and contaminate food and water. Unlike some parasites, E. coli does not form spores or produce oocysts. Properly operated chlorine and ultraviolet (UV) disinfection systems can effectively inactivate E. coli in drinking water.

Once humans consume food or water contaminated with disease-causing E. coli, even a small number of bacteria may cause infection, depending on the strain and the individual’s susceptibility. These bacteria can multiply in the body and, in some cases, produce toxins that cause illness.

Typically, patients develop symptoms such as diarrhea, nausea, vomiting, severe abdominal cramps, and sometimes fever within 1 to 10 days of exposure to E. coli. Some infections may lead to serious complications, including hemolytic uremic syndrome (HUS), which can cause kidney damage. Most people recover within 5 to 10 days, although the duration and severity of illness vary depending on the strain and the individual.

Therefore, infection can pose a serious, life-threatening risk, particularly to young children, older adults, and people with weakened immune systems. However, serious complications can also occur in otherwise healthy individuals.

Most importantly, although some patients may experience long-term health complications, including kidney problems following severe infection, the majority of people recover completely. It is incorrect to claim that most patients suffer permanent liver or kidney damage.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026