First Study: Howell and Colleagues
"The incidence and severity of Clostridium difficile infections are increasing," write Michael D. Howell, MD, MPH, and colleagues from Beth Israel Deaconess Medical Center in Boston, Massachusetts. "Acid-suppressive therapy has been suggested as a risk factor for C difficile, but this remains controversial."
In this pharmacoepidemiologic cohort study, the investigators conducted a secondary analysis of prospectively collected data from 101,796 patients who were discharged from a tertiary care medical center during a 5-year period. Acid suppression treatment was the primary exposure of interest, classified by intensity (no acid suppression, histamine2-receptor antagonist [H2RA] treatment, daily PPI use, and PPI use more often than daily).
The risk for nosocomial C difficile infection increased with increasing level of acid suppression. This risk was 0.3% (95% confidence interval [CI], 0.21% - 0.31%) in patients not receiving acid suppressive treatment, 0.6% (95% CI, 0.49% - 0.79%) in those receiving H2RA treatment, 0.9% (95% CI, 0.80% - 0.98%) in those using PPIs daily, and 1.4% (95% CI, 1.15% - 1.71%) in patients using PPIs more often than daily.
The association persisted after adjustment for comorbid conditions, age, antibiotics, and propensity score–based likelihood of receiving no acid suppression treatment. The odds ratio was 1 for no acid suppression (reference), 1.53 for H2RA treatment (95% CI, 1.12 - 2.10), 1.74 for daily PPI use (95% CI, 1.39 - 2.18), and 2.36 for more frequent PPI use (95% CI, 1.79 - 3.11). A matched cohort analysis and nested case-control techniques resulted in similar estimates.
"Increasing levels of pharmacologic acid suppression are associated with increased risks of nosocomial C difficile infection," the study authors write. "This evidence of a dose-response effect provides further support for the potentially causal nature of iatrogenic acid suppression in the development of nosocomial C difficile infection."
Limitations of this study include observational design, possible residual confounding or selection bias, and lack of data about use of acid suppressive medications or antibiotics before admission.
Second Study: Linsky and Colleagues
The second study, by Amy Linsky, MD, from Boston Medical Center in Massachusetts, and colleagues, was a retrospective cohort study using administrative databases of the New England Veterans Healthcare System. From October 1, 2003, through September 30, 2008, there were 1166 inpatients and outpatients treated with metronidazole or vancomycin hydrochloride for incident C difficile infection.
Of these patients, 527 (45.2%) were given oral PPIs within 14 days of diagnosis, and 639 (54.8%) were not. The investigators measured the hazard ratio (HR) for recurrent C difficile infection, which was defined as a positive toxin result in the 15- to 90-day period after incident C difficile infection.
Compared with patients not using PPIs, those using them were more likely to have recurrent C difficile infection (25.2% vs 18.5%), with an adjusted HR of recurrent C difficile infection of 1.42 (95% CI, 1.11 - 1.82), based on Cox proportional survival methods.
Among patients exposed to PPIs, risks for recurrent C difficile infection were highest among those older than 80 years (HR, 1.86; 95% CI, 1.15 - 3.01) and among those given antibiotics not targeting C difficile during follow-up (HR, 1.71; 95% CI, 1.11 - 1.64).
"...PPI use during incident CDI [C difficile infection] treatment was associated with a 42% increased risk of recurrence," the study authors write. "Our findings warrant further studies to examine this association and careful consideration of the indications for prescribing PPIs during treatment of CDI."
Limitations of this study include use of observational databases, possible misclassification of exposure, and potential misclassifications of a positive test result for C difficile toxin alone as a clinically relevant recurrence.
Editorial: Risk Increase Not Modest
In an accompanying editorial, Mitchell H. Katz, MD, from the San Francisco Department of Public Health, San Francisco, California, describes these studies as well as the others described in the series, "Less Is More."
"The increases in the risk of Clostridium difficile infection with PPIs are not at all modest, reflecting the likely importance of gastric acid in protecting against infection from this pathogen," Dr. Katz writes.
"A pharmacoepidemiologic study of more than 1,000,000 hospital discharges in this issue of the Archives demonstrates a dose-response curve between level of acid suppression and C difficile infection.... Another article in this issue extends this association by demonstrating that the use of PPIs during treatment for C difficile infection was associated with a 42% increase in the rate of C difficile recurrence."