People with cystic fibrosis have a high prevalence of asymptomatic carriage of toxigenic C. difficile, an Australian study has shown.

However, while 30% of asymptomatic CF patients tested at a WA centre had toxigenic C. difficile colonisation, there was no evidence of cross-infection or healthcare facility contamination, said researchers from the Department of Respiratory Medicine, Sir Charles Gairdner Hospital.

The findings are derived from stool samples collected from 66 patients (33 symptomatic and 46 asymptomatic for C. difficile infection) at the WA Adult Cystic Fibrosis Centre.

In asymptomatic patients the prevalence of toxigenic and non-toxigenic C. difficile colonisation was 30% and 24%, respectively. The prevalence of toxigenic C. difficile infection for patients with abdominal symptoms  was 33% (11/33 patients).

Factors that were significantly associated with asymptomatic toxigenic C. difficile carriage included impaired glucose tolerance or diabetes  (P=0.005), and length of IV antibiotics use (P=0.006) . There was also a trend (p=0.05) towards higher CFTR modulator use among patients with C. difficile infection compared to the asymptomatic toxigenic C. difficile carriers and the non-carrier group.

Extensive sampling of inpatient and outpatient areas of the CF clinic showed no evidence of toxigenic C. difficile contamination, and only 3% of samples were positive  for non toxinogenic C. difficile.

Molecular typing for C. difficile ribotypes showed no evidence of person-to-person cross infection within the clinic.

The study investigators said the high prevalence of asymptomatic C. difficile carriage in CF may be attributable to alterations in the gut microbiome, since people with CF were known to have lower species diversity and temporal stability than healthy populations.

“Frequent antimicrobial exposure, gastrointestinal inflammation, increased faecal fat content and CFTR dysfunction contribute to gut dysbiosis in patients with CF and are potential risk factors for C. difficile colonisation and infection,” they wrote.

They also noted that despite high rates of C. difficile colonisation, the incidence of infection in CF was relatively low.

“This may be due to protective humoral immunity as a result of chronic C. difficile colonisation,” they suggested.

The possible link between use of CFTR modulators and symptomatic C. difficile infection might be due to CFTR modulators normalising the gut response to C. difficile toxin, resulting in secretory diarrhoea, the researchers said.

“Alternatively, it could be attributable to treatment bias of CFTR modulators for patients with more severe disease,” they added.

“Given the prevalence of C. difficile in CF, modified C. difficile screening, diagnostic and treatment guidelines tailored to the CF population are needed to improve test specificity, optimise infection control and avoid overtreatment,” they concluded.

The findings are published in the Journal of Hospital Infection.