A recent study has found a somewhat surprising link between anaerobic blood infections and colon cancer. The study will be presented at the 2020 European Congress of Clinical Microbiology and Infectious Diseases. The study found that the link seemed stronger for older persons, which may change colon cancer screening standards for such persons.

Anaerobic bacteria, unlike its aerobic cousin, does not require oxygen to function and can normally be found in the digestive system and other locations.

The study was on a large scale, with over 2 million participants in Denmark from 2007 to 2016. Reviewing data from more than 45,000 blood infections, and then matching this information with all reports of colon cancer over the same period, the researchers found that the presence of anaerobic bacteria meant a significant increase in risk of colon cancer. 

The study report 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 researchers concluded that, in individuals found to have anaerobic blood infections, a recommendation should be made for increased screening for colon cancer.

Interestingly, the researchers could not determine whether the anaerobic blood bacteria were a cause of the colon cancers, or whether the cancers themselves resulted in the infections. The study report has not yet been peer reviewed, so further work is needed to determine the validity of its conclusions.