BOSTON – No winter spike in Clostridium difficile infection (CDI) rates was seen among hospitalized patients after testing methodologies and frequency were accounted for, according to a large multinational study.
A total of 180 hospitals in five European countries had wide variation in CDI testing methods and testing density. However, among the hospitals that used a currently recommended toxin-detecting testing algorithm, there was no significant seasonal variation in cases, defined as mean cases per 10,000 patient bed-days per hospital per month (C/PBDs/H/M). The hospitals using toxin-detecting algorithms had summer C/PBDs/H/M rates of 9.6, compared to 8.0 in winter months (P = .27).
These results, presented at the annual meeting of the American Society for Microbiology by Kerrie Davies, clinical scientist at the University of Leeds (England), stand in contrast to some other studies that have shown a wintertime peak in CDI incidence. The data presented help in “understanding the context in which published reported rate data have been generated,” said Ms. Davies, enabling a better understanding both of how samples are tested, and who gets tested.
The study enrolled 180 hospitals – 38 each in France and Italy, 37 each in Germany and the United Kingdom, and 30 in Spain. Institutions reported patient demographics, as well as CDI testing data and patient bed-days for CDI cases, for 1 year.
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Current European and U.K. CDI testing algorithms, said Ms. Davies, begin either with testing for glutamate dehydrogenase (GDH) or with nucleic acid amplification testing (NAAT), and then proceed to enzyme-linked immunosorbent assay (ELISA) testing for C. difficile toxins A and B.
Other algorithms, for example those that begin with toxin testing, are not recommended, said Ms. Davies. Some institutions may diagnose CDI only by toxin detection, GDH testing, or NAAT testing.
For data analysis, Ms. Davies and her collaborators compared CDI-related PBDs and testing density during June, July, and August to data collected in December, January, and February. Testing methods were dichotomized to toxin-detecting CDI testing algorithms (TCTA, using GDH/toxin or NAAT/toxin), or non-TCTA methods, which included all other algorithms or stand-alone testing methods.
Wide variation was seen between countries in testing methodologies. The United Kingdom had the highest rate of TCTA testing at 89%, while Germany had the lowest, at 8%, with 30 of 37 (81%) of participating German hospitals using non–toxin detection methods.
In addition, both testing density and case incidence rates varied between countries. Standardizing test density to mean number of tests per 10,000 PBDs per hospital per month (T/PBDs/H/M), the United Kingdom had the highest density, at 96.0 T/PBDs/H/M, while France had the lowest, at 34.4 T/PBDs/H/M. Overall per-nation case rates ranged from 2.55 C/PBDs/H/M in the United Kingdom to 6.9 C/PBDs/H/M in Spain.
Ms. Davies and her collaborators also analyzed data for all of the hospitals in any country according to testing method. That analysis saw no significant difference in seasonal variation testing rates for TCTA-using hospitals (mean T/PBDs/H/M in summer, 119.2 versus 102.4 in winter, P = .11), and no significant seasonal variation in CDI incidence. However, “the largest variation in CDI rates was seen in those hospitals using toxin-only diagnostic methods,” said Ms. Davies.
By contrast, for hospitals using non-TCTA methods, though testing rates did not change significantly, incidence was significantly higher in winter months, at a mean 13.5 wintertime versus 10.0 summertime C/PBDs/H/M (P = .49).
One country, Italy, stood out for having both higher overall wintertime testing (mean 57.2 summertime versus 78.8 wintertime T/PBDs/H/M, P = .041), and higher incidence (mean 6.6 summertime versus 10.1 wintertime C/PBDs/H/M, P = .017).
“Reported CDI rates only increase in winter if testing rates increase concurrently, or if hospitals use nonrecommended testing methods for diagnosis, especially non–toxin detection methods,” said Ms. Davies.
The study investigators reported receiving financial support from Sanofi Pasteur.
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