Bacterial Blood Infections Tied to Heightened Colon Cancer Risk

Colorectal cancer occurs in the colon or the rectum and it is the third most common type of cancer in the USA. Around 90% of cases occur in people aged 50 years or older. As well as age, risk factors include a family history of colorectal cancer, some genetic syndromes, obesity, and a lack of exercise, a diet low in fruit and vegetables, and inflammatory bowel disease.

Anaerobic bacteria, unlike aerobic bacteria, do not require oxygen in order to function. They are a normal part of the human body, existing in various locations, including the gut. They usually do not cause infections, but when they do, it is most often in the area that the bacteria inhabit. A new study indicates that there is an association between blood infections caused by certain types of bacteria and an increased risk of colon cancer.


A team of scientists associated with Odense University Hospital (Odense, Denmark) gathered data on 45,760 blood infections, including information about the type of pathogens present in the participants’ bloodstreams. Of the 45,760 people who had a bacterial blood infection, 492 (1.1%) later developed colorectal cancer. Of these, 241 (0.5%) were within the first year of the bacterial blood infection. The team matched each of these people by age and sex to a control group of five people who had not had a blood infection.

The investigators reported that compared to people with blood infections caused by aerobic bacteria such as Escherichia coli or Staphylococcus aureus or people without blood infections, those anaerobic bacteria associated with an increased risk of colorectal cancer were: Clostridium septicum (tied to a 42-times increased risk within a year after a blood infection, and a 21-times higher risk overall); and Bacteroides ovatus, (tied to a 13-times increased risk within a year after a blood infection, and a six times higher risk overall).

Ulrik Stenz Justesen, MD, a Clinical Microbiologist and senior author of the study, said, “At this stage we are not sure if the bacteria are directly causing cases of colorectal cancer, or if the blood infection with these bacteria is itself caused by the cancer. It's an example of the question 'is this the chicken or the egg? With regards to screening, if we saw these high risk bacteria in combination with advanced age, then it would definitely be worth screening the person for colorectal cancer.” The study was slated to be presented at the European Congress of Clinical Microbiology and Infectious Diseases which was to be held Apr 18 - 21, 2020 in Paris, France.

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Odense University Hospital