WEDNESDAY, April 22, 2020 (HealthDay News) -- There's an association between blood infections caused by certain types of bacteria and an increased risk of colon cancer, a new study finds.
"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?'" said study leader Dr. Ulrik Stenz Justesen of Odense University Hospital in Denmark.
In any case, the findings might help improve screening for colon cancer, he and his team members said.
They analyzed data from more than 2 million people in Denmark, and found that people with blood infections caused by specific "anaerobic" species of bacteria had up to a 42 times higher risk of getting colon cancer than those with blood infections caused by aerobic bacteria.
Anaerobic bacteria do not require oxygen and live in various environments, including the human gut, where they usually do not directly cause infections.
Prior studies have reported a link between certain anaerobic bacteria and colon cancer, the researchers noted. Their study was scheduled to be presented at the now-canceled European Congress of Clinical Microbiology and Infectious Diseases (ECCMID). This and other studies to be presented will be published in an abstract book by congress organizers.
Compared to people with blood infections caused by aerobic bacteria such as E. 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).
Justesen said that in his clinical microbiology department there are usually two cases of blood infection caused by these anaerobic bacteria identified each week. The infections are usually caused by a breach in the intestinal wall, which can itself be caused by cancer, he noted.
So, "our follow up research of this study will focus on the specific bacteria from cancer patients to see if we can identify specific characteristics that could be implicated in cancer development," Justesen said in an ECCMID news release. "If this is the case it could be of great importance when it comes to screening and treatment of colorectal cancer."
Two U.S. experts in gastrointestinal cancers who reviewed the findings agreed that the jury is still out on whether the bacteria cause cancer.
Still, "since the risk of developing colon cancer was reported at more than 20% within one year of [testing positive for] anaerobic bacteremia, it seems wise to recommend colon cancer screening in all patients within one year of said infection," said Dr. David Bernstein. He's chief of hepatology at North Shore University Hospital in Manhasset, N.Y.
Dr. Richard Whelan is chief of colorectal surgery and colorectal cancer at Northwell Health Cancer Institute in New York City. He stressed that only "a small percentage of people get sick enough such that blood cultures [for the bacteria] would be taken, and an even smaller percentage will have positive cultures. Thus, these findings apply to a very small part of the overall population."
And Whelan added that colon cancer can take years to develop, so it's unclear whether or not the tumor is the cause of the bacterial infection, or the other way around.
"Larger similar studies should be done to confirm these results," he said.
The American Cancer Society has more on colon cancer.
SOURCES: Richard Whelan, M.D.,chief, colorectal surgery and colorectal cancer, Northwell Health Cancer Institute, New York City; David Bernstein, M.D., vice chairman, medicine, and chief, hepatology, North Shore University Hospital, Manhasset, N.Y.; European Congress of Clinical Microbiology and Infectious Diseases, news release, April 20, 2020