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Dear Colleagues, dear Michael,
Since my post last week, I had another look at the numbers in this paper. I found the following:
The measured primary outcomes, according to the paper’s Methods section, were (a) any HAIs and (b) colonization with methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant enterococci (VRE).
Reported in the Results section and in Table 2 were the total (i.e. combined for both trial arms) numbers of patients who had (a) HAI, (b) colonization, (c) both HAI and colonization (i.e. meaning only those patients who had both events occurring together), (d) HAI and/or colonization (i.e. the number of patients who had either HAI or colonization or both together, meaning any event), (e) HAI only but no colonization (i.e. number of patients who had HAI minus the ones who had both HAI and colonization), and (f) colonization only but no HAI (i.e. number of patients who had colonization minus the ones who had both HAI and colonization). I know this may be confusing, but these are the numbers that were reported. They didn’t call if (a)-(f), that is what I am writing here to make the figures more distinguishable.
Separate data for outcomes in each trial arm were only reported for (d), (e) and (f). For (d), the article reported what amounted to a 49% reduction in the copper rooms vs. non-copper rooms (21 vs. 41 patients; p.02), for (e) a 62% reduction in the copper rooms (10 vs. 26; p.013), and for (f), a 67% reduction (4 vs. 12; p.063, NS). What was missing were the numbers of patients with (a) HAI and (b) colonization, listed separately for each trial arm.
The article concluded — in the Discussion section — that copper surfaces in rooms reduced the risk of HAIs by more than half.
However, arguably, (a) any HAIs and (b) any colonization events, as listed in the Methods, would be biologically and clinically most relevant, and it may not be very informative to combine these two events (under d) in the same statistical calculation, because they are biologically and clinically different from each other.
What is listed in Table 2 as “HAI only” (figure e) is actually: “number of patients with HAI minus the number of patients who had both HAI and colonization together”. This — again arguably — is an artificially constructed number without clinical/biological relevance.
Similarly, what is listed in Table 2 as “Colonization only” (figure f) is actually: “number of patients with Colonization minus the number of patients who had both HAI and colonization together”.
I extracted the missing numbers from the other numbers presented and arrived at (a) HAIs 17 vs. 29, and (b) colonization, 11 vs. 15 events. Putting these into my statistics calculator, they were — non-significant.
Regards, Matthias.
—
Matthias Maiwald, MD, FRCPA
Consultant in Microbiology
Adj. Assoc. Prof., Natl. Univ. Singapore
Department of Pathology and Laboratory Medicine
KK Women’s and Children’s Hospital
100 Bukit Timah Road
Singapore 229899
Tel. +65 6394 8725 (Office)
Tel. +65 6394 1389 (Laboratory)
Fax +65 6394 1387
—–Original Message—–
Hi Michael,
Very interesting study. Sometimes it is difficult to get one’s head around things and figure out whether one’s own thinking is correct. I have the following thoughts concerning the study, but do not know if my thoughts are correct:
I can think of the following three routes for transmission of HAIs:
– (i) Endogenously, from within the patient’s own flora (nosocomial UTIs would be typical)
– (ii) Exogenously via direct transfer, e.g. handborne transmission
– (iii) Exogenously via surfaces and secondary transmission from contaminated surfaces
The authors assessed two (actually three) things: (a) HAIs, independent of the organism, (b, c) colonisation with MRSA and VRE.
All three pathways can lead to (a), while only the exogenous pathways can lead to (b, c), because MRSA and VRE cannot arise spontaneously in a non-colonised patient.
The copper surfaces would only reduce the proportion of (a, b, c) due to the second exogenous pathway (iii), but not due to the others (they simply cannot).
If there is a 58% reduction of HAIs through copper surfaces, that would potentially mean that the overall proportion of transmission pathways (i) and (ii) among all HAIs would only be 42% (is that correct?).
My impression always used to be that the endogenous pathway and the exogenous pathway via direct transmission are important, but I have not seen recent estimates of the proportions of all three.
Other observations are that the overall number of HAIs is relatively small, that among the bloodstream infections in the non-copper rooms, there are 3 with coag.-neg. staphs, that among the HAIs in the non-copper rooms are 5 “other” undefined HAIs (among a total of only 26), and that the authors in the abstract combine both HAIs and colonisation events in the same statistics (one p value for both events). A friend who knows about statistics tells me that one should not combine things that are biologically different in the same statistical calculation, and HAIs and colonisations are biologically different.
Any additional thoughts? Again, not sure if my line of thinking is correct.
Best regards, Matthias.
—
Matthias Maiwald, MD, FRCPA
Consultant in Microbiology
Adj. Assoc. Prof., Natl. Univ. Singapore Department of Pathology and Laboratory Medicine KK Women’s and Children’s Hospital
100 Bukit Timah Road
Singapore 229899
Tel. +65 6394 8725 (Office)
Tel. +65 6394 1389 (Laboratory)
Fax +65 6394 1387
—–Original Message—–
I would be interested in other infection control and prevention professionals’ thoughts about the article below. I must admit a healthy dose of scepticism to any study mainly funded by a lobby group (Copper Development Foundation), but the science and methods seems reasonable to me. What is the considered role of the ICU environment in HAI’s? More studies of these effects seem warranted. Are there any similar studies being conducted in Australia currently?
Cheers
Michael
Michael Wishart
CNC Infection Control
Holy Spirit Northside Private Hospital
627 Rode Road, Chermside, Qld 4032
t: (07) 3326 3068 | f: (07) 3607 2226
e: Michael.Wishart@hsn.org.au
w:www.holyspiritnorthside.org.au
Please consider the environment before printing this email
US Study Shows Copper Cuts Hospital Infections by 58%
A 4-year study in the U.S. has shown that using Antimicrobial Copper surfaces in hospital rooms reduced the number of Healthcare Acquired Infections (HAIs) by 58% compared to rooms without Antimicrobial Copper.
The U.S. Department of Defense funded study compared rooms with and without Antimicrobial Copper objects in Intensive Care Units at three major hospitals-The Medical University of South Carolina, Memorial Sloan-Kettering Cancer Center in New York City and the Ralph H. Johnson Veterans Affairs Medical Center in Charleston, South Carolina.
The results, which have been published online in the Infection Control and Hospital Epidemiology (ICHE) Journal, compared copper to equivalent non-copper touch surfaces during active patient care between routine cleaning and sanitizing.
The study confirmed that Antimicrobial Copper surfaces can continuously kill 83% of bacteria that cause HAIs within 2 hours, including drug resistant strains that are often called ‘superbugs’.
“Because the antimicrobial effect is a continuous property of copper, the re-growth of deadly bacteria is significantly less on these surfaces, making a safer environment for hospital patients, “said Dr. Michael Schmidt, Vice Chairman of Microbiology and Immunology at the Medical University of South Carolina and one of the authors of the study.
HAI’s are a major and growing problem worldwide. Here in Australia around 9,000 people die as a result of picking one up in hospital.
“We’ve known for a while that copper and copper alloy surfaces can kill off bacteria and viruses within hours of contact, but we now have proof that they also cut the risk of picking up an infection and that will save lives and cut health care costs,” John Fennell from the International Copper Association said.
“Antimicrobial Copper surfaces and products are now being manufactured worldwide, and there’s been a growing number of hospital, medical clinics, aged care facilities and even kindergartens that have installed them as part of their infection control strategies.”
The [full] study can be found at: http://www.jstor.org/stable/10.1086/670207
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