Differential Diagnosis: Pneumococcal Pneumonia Versus Other Etiologies


William Schaffner, MD, and Christina Madison, PharmD, FCCP, AAHIVP provide an overview of the identification and differential diagnosis of pneumococcal pneumonia.

Ryan Haumschild, PharmD, MS, MBA: As we’re looking at or working up a patient that might be suffering or might be infected by pneumococcal pneumonia, the question comes up, how we differentiate that from other respiratory infections like COVID-19? Dr Schaffner, I’d love to hear your thoughts as you’re doing a diagnostic workup for a patient. What are some of the similarities and differences, and what is the gold standard test that you can utilize to diagnose pneumococcal pneumonia?

William Schaffner, MD: That’s actually a challenging question. The first thing is, of course, we’re going to be concerned with a number of different viral infections, including influenza in the winter season. We also have, as you just mentioned COVID-19, and we have a new awareness of the importance of RSV [respiratory syncytial virus] infections in older adults, never mind a bunch of other viral infections, adenoviruses, rhinoviruses, and the like. The first thing we’ll be doing is trying to make sure whether your patient does or does not have one of these viral infections. So we’ll be going to be doing an awful lot of testing for viral infections. Now, bacterial infections can complicate viral infections and, of course, pneumococcal infections can occur de novo. So how do we diagnose pneumococcal infections, particularly community-acquired pneumococcal infections? You’re not in the hospital. You’re in a clinic, a doctor’s office. This is not so easy. It is generally assumed that the most common bacterial cause of pneumonia that we see in a doctor’s office is still caused by pneumococci. That’s a common assumption. And many patients will be treated for presumptive pneumococcal pneumonia based on history and a physical examination. There may not even be, depending upon the resources available, an x-ray. It’s often common that a sputum culture is not obtained. Some patients can’t provide sputum and still, many physicians will treat empirically and many patients as a consequence will get better. If they don’t get better, then they come back and then they’ll work harder to get that sputum culture. Now about sputum cultures… let’s get a deep specimen and send that off to the laboratory. The laboratory does its job and tells us that there are pneumococci present. Does that indicate that you’ve had pneumococcal pneumonia? It makes it more likely, but we have to remember that many of us can carry asymptomatically pneumococci in our throats. So whatever was down in the lower respiratory tract as it came up could have picked up some pneumococci from the throat and provided a positive culture. So the interpretation of sputum culture results is up to the physician. You’re going to have to make that interpretation. If the gram stain shows a lot of polys, and polys that are magnetizing pneumococci, it’s more likely that you’ve got pneumococcal pneumonia. Now that said, if you’re ill enough to get a blood culture and the blood culture is positive, that’s the gold standard. Then everyone would agree that you’ve got a pneumococcal infection. But sputum culture alone, you’re on interpretive grounds. Nonetheless, many physicians will go ahead and treat patients presumptively. This is common practice throughout the United States and many patients get better. If they don’t get better, that’s when more invasive diagnostic procedures are sometimes undertaken.

Christina Madison, PharmD, FCCP, AAHIVP: I really love that you brought up this point around chronic colonization in that oral pharynx because we see this with other infectious processes as well. And not everyone is going to be sick enough that they’re going to have a bacillary load or a bacterial load that is going to be present in a blood sample. So we do have to be a bit of a detective. We need to look at symptoms. We need to look at history. Is this person at risk for invasive pneumococcal disease? In addition to doing some of those testing and also the quality of the sample as somebody who used to work in a tuberculosis clinic, I tell you, some people just don’t want to cough. I’m just so glad that you brought that up from a diagnostic standpoint because it is so important when we’re thinking about whether or not we’re treating these individuals appropriately as well as making sure that we’re not using, for lack of a better term, a bazooka to kill something versus when we can have precision medicine because we have an accurate culture. So thank you so much for that.

Ryan Haumschild, PharmD, MS, MBA: Yeah. It’s a great review of empiric therapy. Start broad and narrow it down. And to make sure that we have the right bug to drug match if we can get that available. Thanks for reviewing that and also going through the difference between sputum and blood and the differences in terms of that differential diagnosis. I think that was a great overview. One of the things that Dr Schaffner said that stood out to me is we can have some patients that are asymptomatic. I know you built upon that point. Dr Madison, I guess the question then becomes what is the average incubation time for pneumococcal infections?

Christina Madison, PharmD, FCCP, AAHIVP: Yeah, again, we talked about this before. It’s very similar to some of our other infections. Anywhere from 48 to 72 hours is common. You can see a slightly larger incubation period if they have a higher load of organism. But again, it’s fairly quick when we think about the time frame that it takes for somebody to become infected with this. And again, it’s from those respiratory droplets, which we’ve talked about before. We always want to cover a cough. Make sure we’re washing our hands. Those kinds of things. Because I think that’s what causes the spread and you see more infections during times when we are in high congregate settings, where people want to stay indoors. When it’s warm outside we like to go and be outside, but when it gets cold that’s when we all start to congregate. And that’s when you see more of these infections coming out, especially in our elderly folks.

Ryan Haumschild, PharmD, MS, MBA: My follow-up question to that is, what do you look for in patients with pneumococcal infections when considering if they should be hospitalized or not?

Christina Madison, PharmD, FCCP, AAHIVP: I think that goes back to whether or not they are having respiratory symptoms. Also if we’re seeing mental status changes in the elderly, 100%, we definitely, at that point, would want to hospitalize. But we’ve really seen during the pandemic that we don’t want to miss that critical window where somebody may be able to convalesce at home versus them having a reduction in their oxygenation. And we saw this in particular in our persons of color where that pulse ox [oximeter] maybe didn’t have the best reading and really wanting to look at symptomology as well as some of that respiratory information that we’re getting. But if you see somebody who is desatting or if they’re having labored breathing, absolutely, that person should be seeking more acute care. Because now we’re at the point where this infection is now encroaching on this person’s ability to breathe. That can turn very quickly and then lead to the potential need for mechanical ventilation, which I’m sure my colleague can speak to as the hospitalist on our panel here.

Mary Bridgeman, PharmD, BCPS, BCGP, FASCP: Absolutely.

William Schaffner, MD: Ryan.

Ryan Haumschild, PharmD, MS, MBA: Yes.

William Schaffner, MD: Let me just add to that, that was a wonderful discussion. I would just ask, who’s the person affected? Are they immunocompromised? Are they older? Do they have 2 or 3 underlying chronic illnesses? We would be more inclined to hospitalize those fragile patients or just the reason that Dr Madison said, because they may, if you will use this term, go sour very, very quickly.

Christina Madison, PharmD, FCCP, AAHIVP: Yeah. It’s really a fine line between them being able to convalesce at home, being able to provide antibiotics, or a course of therapy vs really requiring that additional supportive care that may need to be supplemental oxygen before they get to the point where they may require mechanical ventilation.

Transcript edited for clarity.

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