As well as age, risk factors include a family history of colorectal cancer, some genetic syndromes, obesity, 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.
The authors of the new study note that previous research had linked specific types of anaerobic bacteria with colorectal cancer. The researchers wanted to further explore this link through a large-scale study.
The study took place in two regions of Denmark between 2007 and 2016. It involved over 2 million participants.
For the analysis, the team gathered data on 45,760 blood infections, including information about the type of pathogens present in the participants’ bloodstreams.
The authors then compared this information with data from the Danish Colorectal Cancer Group Database. In particular, they looked for new cases of colorectal cancer, especially those that developed following a blood infection from any of the bacteria already associated with colorectal cancer.
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 researchers matched each of these people by age and sex to a control group of five people who had not had a blood infection.
The study authors found that anaerobic bacterial blood infections were associated with a significant increase in the risk of colorectal cancer.
For example, those who had a Clostridium septicum infection were 42 times more likely to develop colorectal cancer within the next year.
Only 0.5% of the control group, who had not had a bacterial infection, developed colorectal cancer, compared with 20.8% of those who had a C. septicum infection.
As the study authors conclude in their paper: “In this large scale cohort study, it was found that, in [people] with blood infections caused by selected anaerobic bacteria, the risk of developing colorectal cancer was increased by up to 42 times compared with [people] with blood infections caused by aerobic bacteria such as [Escherichia coli] or [Staphylococcus aureus] or negative controls.”
“The discovery of blood infections with certain anaerobic bacteria could potentially result in a recommendation of screening for colorectal cancer in selected [individuals].”
Study co-author Dr. Ulrik Justesen, from Odense University Hospital in Denmark, notes that although there was a clear link between anaerobic bacterial infections of the blood and colorectal cancer, it was not clear what the causal relationship was between them.
In Dr. Justesen’s words: “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?’”
Looking ahead, Dr. Justesen and team want to gain more detail on bacteria in people with cancer.
He says: “Our follow-up research of this study will focus on the specific bacteria from [people with cancer] to see if we can identify specific characteristics that could be implicated in cancer development. If this is the case, it could be of great importance when it comes to screening and treatment of colorectal cancer.”
This may mean that screening for colorectal cancer could be more effective. According to Dr. Justesen, “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.”
Although the results are interesting, this research is awaiting presentation at a scientific conference. Therefore, details about the full methodology and results are not yet available.
The researchers have not yet written a full paper, and the results have not gone through peer review. Because of this, it is not possible to scrutinize the findings in full.
