In this study, we investigated whether intrahospital room transfers were an independent risk factor for developing hospital-acquired CDI, in a setting with a low number of hospital beds with a high turn-over of patients, and low antibiotic prescriptions rates. Our results suggest that time spent hospitalized is the most important risk factor for healthcare facility-associated CDI, which is supported by previous studies.16–18 The reasons for this, however, are not clear. Being admitted to, and staying at, a hospital is correlated with risk factors such as age, antibiotics, and comorbidities, but also possibly to a higher risk of encountering C. difficile spores. Indeed, Pai et al19 found that in-hospital CDI cases showed clear spatiotemporal clustering while aspiration pneumonia did not. A recently published case-control study found a statistically significant connection between intrahospital transfers and healthcare-onset CDI risk.20 Furthermore, a recent retrospective cohort study with network analysis found that inpatient mobility, along with other factors, could predict CDI risk at the unit level.21 Although we did not find a statistically significant effect modification of intrahospital transfers on the risk of hospital stay duration, this hypothesis might be worthwhile to test in larger patient materials and with more sensitive diagnostic methods.
Given the known importance of age as a risk factor for CDI,22 the lack of a statistically significant difference regarding this variable was somewhat unexpected. The 30-day mortality rate was also similar and high in both groups, reflecting that patients tested for CDI quite often are near the end of their lives. The results for CDI patients are in line with a 2012 review on 30-day all-cause mortality which found a range of 9–38% in 24 studies.23 The similarities between cases and controls in our study may suggest a representative control group drawn from a restricted population of hospitalized patients with suspected CDI, but could also reflect the diagnostic method – well-based enzyme immunoassay toxin tests have a sensitivity around 60–70 %24 and are usually not recommended as standalone tests for CDI. Thus, the control group may include a significant number of false negatives, who would have been included in the case group had a more sensitive method been used. Incorrectly classifying true cases as controls is a measurement error that may dilute true differences between cases and controls.
The main strengths of this study are that all CDI cases during two years were accounted for, with little information loss, and all data were individually extracted from primary sources. Characteristics of the rooms which patients occupied add new insight to the factors contributing to hospitalization being an important risk factor for CDI. Limitations of the study include the limited number of cases and controls which restricts the power. This is the likely explanation for the absence of statistically significant differences in this analysis for the established risk factors antibiotic treatment and PPI use, where confidence intervals were wide. The diagnostic method used, likely leading to misclassification of some cases as controls as mentioned above, is another limitation.