CAP TODAY Pathology/Laboratory Medicine/Laboratory Management
May 2020—Specimen collection, supplies, and serological tests were on the table when CAP TODAY publisher Bob McGonnagle spoke recently with J. Michael Miller, PhD, D(ABMM), director of Microbiology Technical Services, Dunwoody, Ga.
Dr. Miller was with the CDC for 35 years in various roles, among them as chief of the Epidemiology and Laboratory Branch, chief of the Laboratory Response Branch, and chief laboratory science officer for the National Center for Emerging and Zoonotic Diseases. Here is what McGonnagle and Dr. Miller talked about, several weeks into the pandemic.
Have you heard about a problem with sample collection and false-negative results?
“Let’s hope we will be able to stay prepared, should something like this ever occur again.”
Dr. Miller
Dr. Miller: As far as everybody knows there is no “perfect” specimen. There are good specimens, some better than others. But the chronic issue we have with specimens is not so much the specimen itself but the supplies. Nasopharyngeal swabs, for example, are in short supply and that is a chronic issue.
The good news is that for some of these specimens now, patients can collect their own, and that saves the time of health care workers and some of the products that health care workers have to use.
Do you have confidence in patients’ ability to collect a good specimen? Many people would worry about that.
Dr. Miller: We all worry about that, but the specimens patients can collect themselves are simple. It’s just a swab in the nose. These are swabs of the anterior nares (about one cm up the nose) or a midturbinate nasal specimen, using a flocked swab, which is a little further into the nose beyond the anterior nares. And patients can collect their own specimen, or a health care worker can do that, and there are special swabs for each one of those.
For health care workers, the No. 1 specimen we need more than anything else for most testing platforms is a nasopharyngeal swab for swab-based testing. Next would be the throat swab, collected by a health care worker. The nasal midturbinate and the anterior nares specimens are also available if the nasopharyngeal specimen cannot be collected.
We also know this disease can progress to the lower respiratory tract. So some testing platforms will accept sputum, bronchoalveolar lavages, and nasal aspirates.
We know that the organism can be shed in stool so there may be a fecal-oral transmission mechanism. But the primary focus of the illness is respiratory. Upper respiratory first, and then there are some platforms that will accept lower respiratory specimens, but this is where you have to follow the directions of the manufacturer.
For testing developed in the laboratories, some protocols have been updated. They have been validated with one or more of any of those specimens. So the developers tell us the specimens of choice for their platform.
If there was a range of specimens that would be validated on an LDT, and you had no other knowledge, would you preferentially have a well-collected nasopharyngeal swab? Would that be your best specimen?
Dr. Miller: That would be the best specimen, yes. We know that the viral load in a patient is highest during the early stages of the disease, which begins in the upper respiratory tract. So that nasopharyngeal swab is going to be very important.
Many manufacturers have emergency use authorizations, and several have claimed they can use approved specimens, including nasopharyngeal aspirates, nasal aspirates. Does that make sense to you?
Dr. Miller: Yes, it does make sense, especially if their system has been validated with those specimens. And the manufacturer or developer would be able to tell us that. So a nasopharyngeal swab or a nasopharyngeal aspirate could be tested at the discretion of the developer of the test.
Can you give us more detail about what we mean by a nasal aspirate?
Dr. Miller: A nasal aspirate or a nasopharyngeal aspirate is where sterile saline is injected into the nasal or nasopharyngeal area and then it is quickly aspirated. You’re washing out that area and then submitting that fluid for testing.
We have to be careful about which saline we use. For instance, phosphate-buffered saline is probably the saline of choice if saline has to be used to transport a swab, because the pH of phosphate-buffered saline is around 7.0 to 7.2. Regular saline has a pH much lower, down to 5.5 or 5.6. So we want the organism to be as intact as possible with no degradation of its RNA. We are testing for the organism’s RNA, not the organism itself.
In addition to getting the specimen with a swab or a nasal aspirate, we have this question of transporting the specimens to the labs, and I’ve heard reports of shortages of “chemicals.” Do you think in some cases they’re alluding to a shortage of adequate transport media?