Disinfectant Efficacy: Unpacking Concerns Over Joshi Study on C difficile and Bleach Resistance

Researcher working with a microscope and bleach.

(Adobe Stock with AI by Author)

The health care industry was abuzz recently after a study claimed certain Clostridioides difficile strains showed reduced susceptibility to bleach-based disinfectants. This study, published by Loveleen Tina Joshi, PhD, and her team, stirred significant concerns, particularly in infection prevention circles. After speaking with Joshi to explore the issues and implications of this research, Infection Control Today® (ICT®) sat down with Curtis J Donskey, MD, chairman of the Infection Control Committee at Cleveland VA Medical Center, for an exclusive interview.

Joshi is an associate professor of molecular microbiology at the University of Plymouth, UK. She specializes in clinical microbiology and infectious diseases and advises key national groups. Her research is focused on infection prevention and control and molecular diagnostic testing to help tackle the global health care challenge of antimicrobial resistance (AMR).

Beginning The Interview

ICT and Donskey discussed a positive milestone; He was honored this summer (2024) with the Distinguished Scientist Award from the Association for Professionals in Infection Control (APIC). “It was great. APIC is a great group. I have a great deal of respect for them. So, getting an award from them means that [people appreciate] some of the stuff we're doing with infection control. So, I was very touched.”

Donskey is also a professor of medicine at Case Western Reserve University and a staff physician in the Infectious Diseases Section at the Louis Stokes Cleveland VA Medical Center in Cleveland, Ohio.

Donskey Addresses the Joshi Study.

The conversation soon shifted to the core of the interview—Donskey and his team’s response to Joshi’s research, as posted in the American Journal of Infection Control (AJIC), which proposed that certain strains of C difficile may be developing resistance to bleach, a chlorine-releasing agent widely used in health care settings.

Donskey is quick to say that he wants to avoid coming across as being too critical. “We think that it's important to highlight this. There's an issue,” Donskey said.

“We have a couple of concerns, [but] we don't want to scare people. We want to confirm the findings and, if we suspect that this is a product or process problem, that something went haywire. If I were doing a study again and found something that didn't match anything in the literature that's out there, I would confirm it 5 ways and have somebody else confirm it too before I put that out there because I don't want somebody to come back at me and say, “Well, you don't know what you're doing. You used the wrong product.”

So, I'm concerned for her in that regard, and I think she needs to be a little bit more careful. Either that or she has some resistance strains of C difficile, which is exciting, too—terrifying, but exciting. I was surprised that she didn't use other products besides that specific one; if this one didn't work, let's confirm it with another.

ICT had spoken to Joshi previously. "I am an academic researcher. I'm a scientist, and I'm interested in the pursuit of knowledge out of curiosity and to tackle some of the world's greatest challenges like antimicrobial resistance (AMR),” Joshi said. “So, the rationale for doing research like this is to understand whether disinfection is being conducted appropriately and whether there is triggering AMR in microorganisms.

“I've done research in C difficile since 2008,” Joshi continued. “I'm an expert and have done a PhD in the area. In terms of disinfection, for a very long time, I've been very interested in understanding where the C difficile spores survive certain chemical treatments; it goes back to a paper I published in 2012, looking at how spores sit on surfaces and whether they bind to inorganic surfaces or organic surfaces better.”

The findings initially surprised Donskey and his team. “This was contradictory to all our previous work with bleach-based products, and so we were concerned that this could be a real phenomenon, but we also wanted to test whether we wanted to confirm for ourselves. We'd like to replicate those findings, test the same strain, and see if we could replicate those findings because they would have major importance if we could show that that was true.”

Also, to replicate the study, Donskey pointed out that they needed to use EPA-registered bleach products and standardized testing methods, which differed from those used in Joshi’s research. “They didn't use an EPA-registered bleach product, and the protocol was not a standardized test method that we would use, like the ASTM method, and so it makes it very difficult for us to assess how good the product was, was likely to be working and to replicate the method. So that was the issue with that article.”

The Importance of EPA-Registered Products

Why is it crucial to use EPA-registered sporicidal products? Donskey explained that registered products undergo stringent testing to ensure efficacy against pathogens like C difficile. EPA registration also ensures that products maintain a stable concentration over time, which is vital for proper disinfection. If products degrade or are not stored correctly, they can lose effectiveness, which may explain some of the findings in Joshi’s study.

“EPA has a list of standard disinfectants registered with them as sporicidal, including lots of bleach-based products,” Donskey said. “We responded to the article because we were concerned, and we wanted to do is try to replicate those studies, test the same against the same isolates if we could, and with a standard test method.”

Discrepancies in the Study

Donskey noted significant discrepancies between Joshi’s findings and previous literature. Specifically, Joshi’s study reported a low reduction in C difficile spores using bleach products at high concentrations (10,000 parts per million). This contrasts with previous studies that showed the same strain of C difficile being susceptible to chlorine-releasing products, even at lower concentrations.

One key concern raised by Donskey was the study's need for more verification. “So it's not that you can't study—you certainly are welcome to study other bleach-based products, but if you do, it would be necessary; I think that you would conduct some additional testing to confirm that your product has the correct concentration and that you're storing it, and you're either preparing it fresh or that you're assuring every time you do the testing that it has the correct concentration of chlorine or sodium hypochlorite in it.”

Donskey continued, “That's the concern. It would be easy for someone to have an error occur with a product that may be less stable or have a wide range of concentrations; you could end up with results that look funny. If I tested a bleach product, and 100 articles say bleach products work, then there's a K List with 100 sporicidal hypochlorite products. I got a product that didn't work. I would do a very strenuous amount of testing to confirm that that product is working and put that in the article. We did titration. It had the appropriate concentration. We did it every time we ran a test. So, we know that we had a product that was working.”

“That's the main question that came up for all of us who are interested in this area, that it's so if you want to, if you use a non-EPA registered disinfectant, you have to confirm…demonstrate that the product was working, that the concentrations that are appropriate and were stable or were freshly prepared. And then you have to either use a standard test method or describe in detail how you did the study so that other people can replicate exactly what you did to ensure there wasn't some issue with how the study was conducted.”

Next Steps in Research

Moving forward, Donskey emphasized the importance of replicating the study and sharing the resistant strains. One thing that we can do is look at the previous data for the particular strains that she tested. So, we were able to test the same R20291 strain. It's the same strain isolated in the [United Kingdom] 20 years ago, and we included in our response letter a table of different studies that have included this specific test strain that she is now showing is completely resistant to sodium hypochlorite.

Donskey continued, “In that table, we show from these studies that 5 publications looked at that same R20291 strain and if it was susceptible to chlorine-releasing products. It was there that it was effective. And then there are these 2 publications. In fact, [Joshi] showed that the NaDCC [sodium dichloroisocyanurate] was also effective against this strain. Still, they were the 2 recent publications that suggested that this strain is not being killed by sodium hypochlorite.

“So there's a discrepancy in the literature, which would make us think that one of the real considerations here is that the product or the test procedures may have somehow impacted the results. That's how it would be interpreted. The other possibility is that the strains she works with in the lab have developed some mutation. It's the same strain, but some mutation has occurred, and it has now become less susceptible to sodium hypochlorite. To confirm that…one thing that would be helpful would be to share the strain she's using for testing, send it to other labs, and have them confirm her findings. If indeed they find the same thing, then that would confirm those results and show that some strains of C difficile can develop mutations that lead to reduced susceptibility.

Then, Donskey discussed the discussion in social media and infection control circles. “I think Dr Josh's group is a solid research group that has been studying C difficile for years. We still have to consider that what we wanted to demonstrate with our letter is not that they're wrong per se, but we wanted to show that we can test at least the same strain. We can use a standard method and an EPA-registered product and assure people that the products that are registered and on List K here in the US are still effective. We would like to follow up on this as well. So, we have a large collection of C difficile around the country. Her article spurred at least [our team] to do some additional testing to see if there is any concern that, in the US here, we're seeing the emergence of reduced susceptibility.

Additionally, Donskey suggested conducting genetic sequencing of the C difficile strains used in the study to check for mutations that might explain reduced susceptibility. This could help determine whether the strains had developed a resistance or if other factors were at play.

The positive points that have come out of her study, according to Donskey, are “A couple of things, so her study has certainly highlighted the potential for C difficile or other organisms out there to become resistant to disinfectants. Other organisms besides C difficile can become resistant to quaternary ammonium disinfectants, for example. So, this problem deserves ongoing surveillance for the emergence of organisms with reduced susceptibility. Another thing that the work, I think, has highlighted is that we think of bleach as being the perfect disinfectant that wipes out every spore there. They have very nicely pointed out, and we, in our response letter, again looked at the killing of different C difficile spores and demonstrated that lower concentrations of bleach are not much less effective. It takes a longer time to kill C difficile, so if you use a reduced concentration of sodium hypochlorite, or you wet the surface and then wipe it immediately if you don't apply the appropriate contact time, you can then get exactly what she's demonstrating that those spores can then they can be on your clothing. They can stay there and be at risk for transmission.

“I think that is useful to point out because people think of bleach as if every spore is dead, and that's not necessarily the case. It takes some takes. There's a bit of time involved, and the concentration is important. And if we don't achieve the appropriate concentration and the appropriate contact time, they're going to we're not going to achieve the results that we are hoping to get.”

Curtis’s Response to Joshi’s Quote From ICT’s Interview

When ICT spoke with Joshi about their study, she said, "Please read the literature. Understand that [AMR] is an important issue that affects all of us as a species. And it's important for you to understand that genuinely and for the public to understand it. Again, it shows a lot of myths of communication from the academic world and the scientific world to the public. Again, I think there's a disconnect, and we've got to do more to get that message out about antimicrobial resistance."

Curtis responded, “I agree with Dr. Joshi that antimicrobial resistance is an important issue, and it's important not only for health care personnel to understand it, but also to try to get the word out to the public. So I completely agree with that. I think that the work that they've done is important in the sense that it's gotten people talking about disinfectants and the potential for the emergence of resistance to disinfectants. We need to do more work to confirm what they're finding. But they've promoted an important discussion. So, I commend them for that.”

Takeaways for Infection Preventionists

One of the most critical messages from the interview was the need for IPs to remain vigilant. “Let’s do exactly what she's suggesting. Let's make sure that we're not seeing the emergence of reduced susceptibility, that the appropriate concentrations are up there because if you have a concentration that's too low, it won't work, and that people are applying them correctly. I mean, this is an important side effort that's in part come out of this work.”

Donskey also highlighted the importance of education: "Infection preventionists should be aware of these discussions and remain updated on any new research or product guidelines."

Conclusion

While Joshi’s study raised some alarming questions, Donskey urged the health care community to proceed cautiously. He encourages Joshi, her team, and others to continue to investigate possible mutations in C difficile and other pathogens.