Impact of polymerase chain reaction testing on Clostridium difficile infection rates in an acute health care facility

Two rapid methods of Clostridium difficile infection (CDI) diagnosis were compared between June 2012 and March 2013: a GeneXpert (Cepheid, Sunnyvale, Calif) polymerase chain reaction (PCR) test and an enzyme immunoassay (EIA). The influence of these methods on the detection of hospital-acquired CDI and identification of CDI outbreaks was evaluated. We tested 1,592 stool samples for C difficile. The GeneXpert PCR test identified 211 positive samples (68 determined to be hospital-acquired infection), whereas EIA identified 105 positive samples (36 determined to be hospital-acquired infection). The GeneXpert PCR method in contrast to the EIA method increased the detection rates of nosocomial CDI cases and contributed to the declaration of CDI outbreaks. Two rapid methods of Clostridium difficile infection (CDI) diagnosis were compared between June 2012 and March 2013: a GeneXpert (Cepheid, Sunnyvale, Calif) polymerase chain reaction (PCR) test and an enzyme immunoassay (EIA). The influence of these methods on the detection of hospital-acquired CDI and identification of CDI outbreaks was evaluated. We tested 1,592 stool samples for C difficile. The GeneXpert PCR test identified 211 positive samples (68 determined to be hospital-acquired infection), whereas EIA identified 105 positive samples (36 determined to be hospital-acquired infection). The GeneXpert PCR method in contrast to the EIA method increased the detection rates of nosocomial CDI cases and contributed to the declaration of CDI outbreaks. Several laboratory methods are available to diagnose Clostridium difficile infection (CDI), including enzyme immunoassay (EIA)-based tests, stool cultures, and nucleic acid amplification tests. EIA and polymerase chain reaction (PCR) tests are fast methods for CDI diagnosis, but they vary in their sensitivities and specificities.1Peterson L.R. Mehta M.S. Patel P.A. Hacek D.M. Harazin M. Nagwekar P.P. et al.Laboratory testing for Clostridium difficile infection: light at the end of the tunnel.Am J Clin Pathol. 2011; 136: 372-380Crossref PubMed Scopus (52) Google Scholar The use of these methods can affect the correct diagnosis of CDI, patient management, and deployment of infection control protocols. Although there has been a near consensus on the superiority of PCR methods detecting C difficile in terms of sensitivity and turnaround time,2Grein J.D. Ochner M. Hoang H. Jin A. Morgan M.A. Murthy A.R. Comparison of testing approaches for Clostridium difficile infection at a large community hospital.Clin Microbiol Infect. 2014; 20: 65-69Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar many laboratories still use EIA assay mostly due to cost issues. In this report, we compare the EIA and the GeneXpert PCR (Cepheid, Sunnyvale, Calif) test methods and the influence of using these diagnostic tools on CDI rates in a Canadian acute-care facility. All work performed in this study was approved by our Institutional Research Ethics Board. This was an observational study, with a population composed of all patients tested for C difficile by the Microbiology Laboratory at Health Sciences North, Sudbury, Ontario, Canada, between June 2012 and March 2013. During the study period, 978 patients were tested, producing total 1,592 samples tested for C difficile. Health Sciences North is a 500-bed acute-care teaching health care center, where provincial best practice infection prevention and control measures are followed. The definition described by the Ontario Provincial Infectious Diseases Advisory Committee was followed to identify hospital-acquired CDI cases and the declaration of the 2 C difficile outbreaks.3PIDAC Routine practices and additional precautions in all healthcare settingsAnnex C: testing, Surveillance and managment of Clostridium difficile. Provincial Infectious Diseases Advisory Committee, Ontario, Canada2013Google Scholar Only nonformed stools were accepted for C difficile testing. The same stool sample was used to perform the EIA and GeneXpert PCR tests. To perform the EIA assay test we used the ImmunoCard Toxins A and B (Meridian, Memphis, Tenn) and for the PCR assay, the GeneXpert C difficile Epi (Cepheid) test was used. The manufacturer's instructions were followed in both cases. Results were reported as either C difficile toxin detected or C difficile toxin not detected. If the C difficile toxin was detected in a patient sample by either method, or by both, the sample was reported as positive. The EIA and GeneXpert PCR tests were run concurrently in our Microbiology Laboratory. Collected data were used to study the effect of switching the testing methodology on the rates of CDI. Patients tested were evenly split between men and women. More than 80% of the tested samples were from patients older than age 50 years, and about 75% of the tested patients were inpatients. Higher rates of patients with CDI were detected using the GeneXpert platform compared with the EIA method. Unweighted moving average analysis of weekly positive frequency tests with a 2-week periodicity showed this to be a consistent trend (Fig 1). The GeneXpert PCR test detected twice as many CDI-positive cases as the EIA test (n = 211 vs n = 105, respectively) (Fig 1). When compared with the hospital historical figures, this result indicates a sharp increase in the number of patients diagnosed with CDI. From the 211 samples that tested positive for C difficile using the GeneXpert PCR test, 68 samples came from patients who were determined to have hospital-acquired infection by our Infection Prevention and Control Department. Thirty-two hospital-acquired CDI cases tested negative using EIA and 36 were positive using EIA. Two C difficile outbreaks were declared at Health Sciences North during the period between September and December 2012 in 2 wards; an oncology ward (ward A) and a respiratory medical ward (ward B). During the outbreak period, a total of 33 inpatients in the 2 affected wards tested positive for C difficile using either the EIA test or GeneXpert PCR test. Out of the total number, 22 patients were determined to have acquired CDI in these 2 wards (15 in ward A and 7 in ward B). Out of the 22 patients with hospital-acquired CDI, 20 tested positive for C difficile by using the GeneXpert PCR testing platform (2 samples were not available for testing using the GeneXpert PCR test). Only 12 out of the 22 CDI-positive patients tested positive using the EIA method, 9 were negative, and 1 sample was not tested using EIA (Fig 2). In both outbreaks, the number of nosocomial CDI cases initially identified by the EIA method was below the threshold determined by the Ontario Provincial Infectious Diseases Advisory Committee to declare a C difficile outbreak. These results indicate that the identification of the outbreaks would have been delayed in the 2 affected wards if only an EIA test was used at the time (Fig 2, Fig 3). The introduction of a more sensitive, PCR-based method for testing C difficile had a profound influence on the detection and the rate of CDI at Health Sciences North. Using GeneXpert PCR for the testing of CDI contributed not only to the detection of hospital-acquired cases of CDI, but also to the detection of outbreaks. In this report, we show that the GeneXpert PCR test assisted in defining the duration of 2 CDI outbreaks in our facility in 2012. As shown in Fig 2, Fig 3, we identified hypothetical scenarios where only EIA results were used to identify outbreaks. The scenarios show a delay in declaring the outbreaks, and an early end of the outbreaks. A previous study has shown that a “pseudo-outbreak” was declared in a hospital due to a faulty detection kit, leading to many false-positive CDI cases.4Litvin M. Reske K.A. Mayfield J. McMullen K.M. Georgantopoulos P. Copper S. et al.Identification of a pseudo-outbreak of Clostridium difficile infection (CDI) and the effect of repeated testing, sensitivity, and specificity on perceived prevalence of CDI.Infect Control Hosp Epidemiol. 2009; 30: 1166-1171Crossref PubMed Scopus (25) Google Scholar These misidentified cases can drain hospital resources and adversely affect patients. However, our study underlines that using a less-sensitive method to diagnose CDI may increase the chances of spreading C difficile within wards. We also recognize that the high sensitivity of the PCR test has the potential to overdiagnose cases of CDI. A large study in the United Kingdom found that the PCR test used alone may identify colonized patients as having CDI, suggesting the use of a cytotoxin assay in the algorithm to correctly identify patients with hospital-acquired CDI.5Planche T.D. Davies K.A. Coen P.G. Finney J.M. Monahan I.M. Morris K.A. et al.Differences in outcome according to Clostridium difficile testing method: a prospective multicentre diagnostic validation study of C difficile infection.Lancet Infect Dis. 2013; 13: 936-945Abstract Full Text Full Text PDF PubMed Scopus (332) Google Scholar The factors contributing to CDI rates in a hospital are complex. The method used for the detection of C difficile is a major factor in the detection of CDI, and in the declaration and end of outbreaks. Improved diagnostic methods and a robust antibiotic stewardship program,6Dancer S.J. Kirkpatrick P. Corcoran D.S. Christison F. Farmer D. Robertson C. Approaching zero: temporal effects of a restrictive antibiotic policy on hospital-acquired Clostridium difficile, extended-spectrum β-lactamase-producing coliforms and methicillin-resistant Staphylococcus aureus.Int J Antimicrob Agents. 2013; 41: 137-142Abstract Full Text Full Text PDF PubMed Scopus (104) Google Scholar in addition to infection control policies and practices, environmental cleaning,7Guerrero D.M. Carling P.C. Jury L.A. Ponnada S. Nerandzic M.M. Donskey C.J. Beyond the Hawthorne effect: reduction of Clostridium difficile environmental contamination through active intervention to improve cleaning practices.Infect Control Hosp Epidemiol. 2013; 34: 524-526Crossref PubMed Scopus (31) Google Scholar improving hand hygiene practices,8Edmonds S.L. Zapka C. Kasper D. Gerber R. McCormack R. Macinga D. et al.Effectiveness of hand hygiene for removal of Clostridium difficile spores from hands.Infect Control Hosp Epidemiol. 2013; 34: 302-305Crossref PubMed Scopus (48) Google Scholar hospital design,9Simor A.E. Williams V. McGeer A. Raboud J Larios O Weiss K et al.Prevalence of colonization and infection with methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococcus and of Clostridium difficile infection in Canadian hospitals.Infect Control Hosp Epidemiol. 2013; 34: 687-693Crossref PubMed Scopus (32) Google Scholar and better identification of asymptomatic carriers10Leekha S. Aronhalt K.C. Sloan L.M. Patel R. Orenstein R. Asymptomatic Clostridium difficile colonization in a tertiary care hospital: admission prevalence and risk factors.Am J Infect Control. 2013; 41: 390-393Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar should all result in better control of CDI.

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