Wednesday February 8 2012
How C. difficile is transferred in hospital remains unknown
“We don’t know what causes deadly hospital superbug to spread, admit scientists,” the Daily Mail has reported. “Hospitals may be adopting the wrong strategy for combating a notorious bug on the wards,” it goes on to say. This story is based on new research investigating the transmission of Clostridium difficile (C. difficile), a hospital-acquired infection that can be fatal.
C. difficile is thought to be spread in hospital through contact with infected patients, but new UK research has found that this may not be the case. The research found that two-thirds of new cases in hospital were not linked to any cases of patients known to be infected. Less than a quarter of the newly infected patients had the same type of C. difficile infection as a patient on their ward who was known to be infected.
This research challenges the assumption that C. difficile is spread on wards through contact with infected patients. It means that current strategies focusing on preventing person-to-person spread may not stop C. difficile transmission.
This research cannot tell us how good hospital prevention strategies are at stopping C. difficile from spreading. People visiting and being admitted to hospital should continue to follow their hospital’s hygiene advice, particularly regarding hand washing and the use of alcohol hand gels.
Where did the story come from?
The study was carried out by researchers from John Radcliffe Hospital Oxford, the Medical Research Council, the University of Oxford, Leeds General Infirmary and the University of Leeds. It was funded by several academic institutions including the Oxford NIHR BioMedical Research Centre and the UK CRC Modernising Medical Microbiology Consortium.
The study was published in the peer-reviewed journal Public Library of Science: Medicine.
While the Mail accurately reported the study’s findings, it’s headline and introduction may suggest that current infection-control studies are wrong. In fact, infection control studies are useful for combating most bacterial menaces, and may still have a role in halting C. difficile. The headline may also give the impression that scientists have been withholding information and have had to admit that they were wrong. In reality, this is newly published and impressively comprehensive research.
What kind of research was this?
The researchers point out that C. difficile is a leading hospital-acquired infection that can result from antibiotic treatment. This is because antibiotics can disrupt normal healthy gut bacteria allowing C. difficile to multiply rapidly and produce toxins that cause illness. C. difficile causes gastrointestinal problems including diarrhoea, leading to severe illness and even death, especially in older patients and those who are seriously ill.
Following hospital outbreaks of C. difficile worldwide, greater effort has been put into preventing and controlling infection with the bacteria, and this is thought to have reduced incidence. Yet, to date, say the authors, there have been no robust evaluations of whether such strategies are reducing the spread of infection between individuals. The authors argue that a better understanding of person-to-person spread of C. difficile is crucial to reducing the incidence further.
This population-based study was set up to examine in detail transmission in hospital wards, to give better insight into the nature of person-to-person spread and to improve infection-control measures. In particular, it investigated the proportion of new cases of infection arising from ward-based transmission from infected patients.
What did the research involve?
From September 2007 to March 2010, all patients admitted to Oxfordshire hospitals with persistent diarrhoea, and all patients of 65 or older with any diarrhoea, had stool samples taken for C. difficile testing. The researchers tested the samples using specialised laboratory techniques (enzyme immunoassay and culture). Where C. difficile was identified, they used further tests (called multi-locus sequence typing) to identify the particular strains of C. difficile infection.
Based on the similarities and differences in the strains, the researchers used this “genetic fingerprint” of the bug to investigate how it had spread. This approach was based on the assumption that the same strain found in two people was evidence of direct contact between patients on the ward. They constructed potential “networks” of cases and potential routes of transmission for up to 26 weeks, for each strain of C. difficile they had identified. Their analysis was based on infected patients spending time on the same ward.
In order to show how far C. difficile was spread in a ward from person to person, the researchers traced ward contacts between all pairs of cases with the same strain. To reduce the possible bias caused by the same infection occurring spontaneously in a shared ward without contact, the researchers used patients whose stools had tested negative for C. difficile as controls. They analysed the data using standard statistical methods.
What were the basic results?
The researchers tested 29,299 stool samples for C.difficile from 14,858 patients.
- 1,282 (4.4%) samples tested positive for C. difficile
- 69 different types of C. difficile were identified
- most (66%) C. difficile infections were not linked to other known cases with the same strain
- only 23% of cases sharing the same ward shared the same type of C.difficile
How did the researchers interpret the results?
The researchers found that most new cases of C. difficile infection could not be accounted for by contact with other people with C. difficile on the same ward. They say that this means that they cannot be sure that the infection can be controlled by current strategies based on preventing person-to-person spread. Greater understanding of other routes of transmission is needed to determine what type of interventions will prevent the spread of the infection, they argue.
This research is important because it suggests that the previous assumption that all C.difficile is spread on wards through contact with infected patients may not be entirely correct. As the authors point out, this means that transmission may not be adequately controlled by current strategies, which focus on preventing person-to-person spread. Further study is required to look at how the infection is transmitted.
It’s worth noting that the research concentrated on established cases of Clostridium difficile and the potential transmission between infected patients. As such, it did not look at how far C. difficile may have been stopped from spreading in the wards by current hospital prevention strategies.
Infection control measures in the NHS and private hospitals remain valid because they are largely effective at preventing many forms of infection. People going into hospital should continue to follow the stated hygiene procedures, particularly hand washing.