Is Risk of Colorectal Cancer Linked to Certain Blood Infections?

Is there a link between certain anaerobic bacteria and the risk of developing colorectal cancer?

New research from Danish investigators that was slated to be presented at the 2020 European Congress on Clinical Microbiology and Infectious Diseases (ECCMID) this past week suggests there could be. ECCMID’s in person and virtual components were cancelled due to coronavirus disease 2019 (COVID-19), but the congress organizers have released some of the meeting’s abstracts and plan to release more on May 5^th.

Previous research has suggested an association between bacteria from the Bovis group streptococci, Clostridium septicum and colorectal cancer (CRC). However, recently there have been associations reported between CRC and different Bacteroides species, Fusobacterium nucleatum.

As such, the investigators, led by Ulrik Stenz Justesen, Odense University Hospital, Denmark, set out to investigate this association in a large-scale study.

They performed a population-based cohort study which featured blood culture data from more than 2 million individuals in Denmark that was collected from 2007 to 2016.

They combined the data on blood cultures with the national register for CRC and looked for new cases of new cases of CRC that occurred following blood infection with these bacteria. The investigators reported that the risk of incident CRC until 2018 was investigated for Bacteroides spp., Clostridium spp. and Fusobacterium spp and was then compared with Bovis group streptococci, Escherichia coli, Staphylococcus aureus and with controls. Each case was matched by age and sex with 5 controls.

Of 45,760 bacteraemia episodes, 492 (1.1%) were diagnosed with CRC following the bacterial infection. Of these 241 individuals were diagnosed within 1 year.

“Most anaerobic species were associated with a considerable increased risk of CRC (up to 42 times) compared with negative blood cultures,” the investigators wrote.

According to the abstract, C septicum was associated with a 42 times increased risk of CRC within a year (0.5% of controls developing CRC vs 20.8%), and a 21-times risk overall (1.1% controls vs 22.6%).

On the other hand, Bacteroides ovatus was linked to a 13 times increased risk of CRC within a year (0.5% of controls vs 6.7%), and a 6-times increased risk overall (1.1% controls vs 6.7%).

“The discovery of blood infections with certain anaerobic bacteria could potentially result in a recommendation of further evaluation for CRC in selected patients,” the investigators conclude.

However, in a press release Justensen noted that not enough is known about the link right now.

“At this stage we are not sure if the bacteria are directly causing cases of colorectal cancer, of 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?’”

The abstract, Bacteraemia with anaerobic bacteria and association with colorectal cancer, was slated to be presented at ECCMID 2020.