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Experts discuss CIDTs and challenges of disease surveillance
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An increasing proportion of clinical labs are shifting away from culture in favor of culture-independent diagnostic tests, or CIDTs, which is having a significant impact on clinical testing practices and confounding national disease burden estimates. Infectious Disease News spoke with Irving Nachamkin, DrPH, MPH, FAAM, FIDSA, professor and director of the laboratory medicine division at the University of Pennsylvania’s Perelman School of Medicine, and Robin M. Atkinson, PhD, HCLD/PHLD, director of Utah’s Public Health Laboratory, about the transition to CIDTs and challenges of public health surveillance.
To read May’s cover story on the impact of new diagnostics on public health surveillance, click here.
Should the capacity to perform culture tests be maintained, or is the field transitioning into a post-culture diagnostic landscape?
Nachamkin: Clinical laboratories need to maintain culture capabilities for many of the pathogens that are being detected molecularly, particularly the bacterial pathogen. So the challenge is identifying what that capacity should be for various organisms and circumstances.
There are two ways to look at this, one of which would be to look at the model of influenza testing. Most influenza diagnostics now are molecular, and most laboratories have never done cultures for influenza virus. Yet, we need to identify labs that can submit samples either on a regular basis or sporadically to public health labs so they can isolate the virus and type them. That’s an example where not every lab has to have a culture capability, or at least should be able to share samples.
On the other hand, you’ve got things like the enteric pathogen panels that are now coming out of the labs. Normally — for Salmonella, Campylobacter, Shigella, Escherichia coli, etc. — labs have relied on cultures, and once they have those, they do susceptibility testing and send those samples to either local or state laboratories. Without those isolates, public health labs can’t do that kind of work.
I think there is a middle ground. One would be labs using a kind of influenza model where they don’t do the culture and just hold the sample. Then again, in certain circumstances, labs need to have those isolates for susceptibility testing, in which case those isolates should be sent directly to the public health labs. You have to look at each lab, its location and what the current structure is to determine what’s the best model to use.
Atkinson: I’m a classically trained microbiologist. I’m always going to want to default to seeing the culture with actual growth of an organism. Even in this advanced age of technology with PCR, sequencing, etc., someone should maintain the ability to culture.
Until whole-genome sequencing gets a little bit further along, you really can only look for what you know to look for. Being in public health, you always know that there could be something new out there. You could run every extensive PCR or GI panel or whatever it is you have, and you could miss something new if you’re not also trying to do a back-up culture.
There does need to be someone who maintains that expertise and the ability to culture, just for those unknowns when you really don’t know what you’re looking for.
Do clinical and commercial labs have a responsibility to aid surveillance efforts, or is their role limited exclusively to clinical diagnosis?
Nachamkin: I’m a big believer in making sure that clinical laboratories continue to collaborate with public health. They can’t figure out how to do their own surveillance without clinical lab support; they need our help. Clinical labs, whether they’re in a hospital or larger commercial lab, should aid and support public health programs as part of their mission.
The bottom line is we’re all in public health — we’re just improving the public’s health in different ways. I’ve seen discussion by certain labs that feel they should just be involved with diagnostics and not get involved with some of the surveillance activities, and I just don’t agree with it. It goes against our global mission of improving health.
Atkinson: I have worked and was trained in a clinical lab before I made the transition to public health, so I’ve seen both sides of it. The difference between a public health lab and a clinical lab is that a public health lab is concerned about what’s happening in the population. We’re not so concerned that patient A has Salmonella and that that patient is treated. What public health cares about is whether the Salmonella isolated from patient A have anything to do with the Salmonella isolated from patient B. We do investigations to see if those match, and then we work with epidemiology partners to figure out whether something is happening in the community we can control. On the flip side, a clinical lab’s main rule is to focus on the Salmonella initially isolated from patient A, and making sure they get the right treatment.
If you take those strict definitions, it’s 100% acceptable that a clinical lab chooses the best test to diagnose someone’s illness. That’s why it’s an ongoing discussion whether or not clinical labs have a role in surveillance, because once they get a diagnosis from a CIDT, they’re done.
What I’ve found is that it depends on whose money is in the clinical lab, and whether or not they agree with the philosophy of looking at things for surveillance purposes, and at least getting those specimens to public health. But they do have a role — they’re the ones that are choosing a methodology that no longer yields an isolate. If they make a decision that cuts off the supply of isolates and information going into public health, then the public health system falls apart. They’re an integral part of the entire process from start to finish, even if they’re primarily there to treat the patient.
Is government or regulatory intervention necessary to preserve culture-based surveillance?
Nachamkin: We already have regulations in terms of reportable diseases and submission of isolates, when available. We know which diseases we have to report to the city and state laboratories, but currently there is no guidance in terms of methodology; there is no requirement that you actually need to do a culture.
However, we need to have government agencies — not necessarily the federal government, but at the state level — discuss with the clinical laboratories the best approach to getting the isolates and other information they need to continue their programs. [The government needs] to work that out, not necessarily through additional regulation, but through agreements with the clinical labs and reference laboratories in their own states. Now, what that might require is funding through the public health system to help continue supporting that infrastructure in hospital laboratories. We currently do not get support from government agencies to do that, and that is an area where, in order to maintain these reporting systems and to have access to some of these important isolates, providing some funding would help with supporting that infrastructure.
It would be very hard to regulate laboratories — to say “you have to do cultures on all these samples” when, in fact, the technology is going the opposite direction. It needs to be public health and hospital partnership to figure that out, but I think government funding would go a long way.
Atkinson: There has been, for many years, mandatory isolate submission laws in most states. For a certain list of pathogens, you have to submit an isolate to your state public health lab or your local public health lab so that they can do the surveillance that is needed. With CIDTs coming on board, one of the routes that the Association of Public Health Laboratories (APHL), CDC and others have taken is that it is time to start to enforce those rules.
Most states do track whether or not the clinical labs are sending in the isolates as they are supposed to, but there are no penalties involved.
Public health is taking the stance that there should be some government involvement, in the form of laws that require mandatory submission. Public health has tried going the regulation route with the FDA about mandatory reflex culture, etc. The compromise reached between the two was that, essentially, the FDA requires any CIDT that is approved put a notice in the package insert that you should follow your state reporting rules.
A clinical lab should not be punished in any way for choosing to use the CIDT, especially if that is what works for their workflow, and works for their patient population. It is nice that the regulators or the FDA are willing to remind people that we have these rules on the books, and we do need to follow those, but that is as far as a regulatory arm needs to go.
Disclosures: Atkinson and Nachamkin report no relevant financial disclosures.