Episode 55- How do we treat CAP in the immunocompromised?

Hello and welcome to Episode 55 of ER-Rx. In this episode, we discuss how to treat community-acquired pneumonia (CAP) in patients who are immunocompromised by reviewing a consensus statement published in the journal “CHEST” in 2020. Which organisms cause CAP in these patients? Can we follow the IDSA CAP guidelines for treatment recommendations? Or do they all just get vancomycin plus Zosyn?

Immunocompromised patients have been excluded from CAP guidelines because these patients need individualized treatment and because they’ve been excluded from prospective trials that are used to support guideline recommendations in the first place. This is unfortunate because the number of immunocompromised patients is increasing due to longer life expectancies of patients with cancer and organ transplants, better recognition of immunocompromising conditions, and the higher number of patients on immune-modulating therapies. It’s estimated that 3% of the adult population in the US is immunocompromised, and up to 30% of hospitalized patients with CAP have immunocompromising conditions. We encounter these patients daily in the ER setting and given the lack of knowledge and guidance on how to treat CAP in these patients, providers and pharmacists are often left confused and more often than not end up ordering broader antibiotics than are necessary.

Knowing that early and adequate treatment of CAP in the general population improves outcomes, the authors of this guideline wanted to apply these same principles to treating patients with immune dysfunction. For the sake of time, I’ll only cover the points most pertinent to us in the ER or ICU setting. For more detailed explanations, please refer to the full guideline.

The first, and arguably, most important point addressed is; which patients with CAP should be considered immunocompromised? The answer is actually fairly simple: patients who have an underlying disease or medical treatment that alters the immune system and puts them at risk of infection with uncommon or opportunistic infections. Although there is no strict consensus, most agree that patients with cancer, those receiving chemotherapy, those with HIV with CD4 counts less than 200 (cells/ microL), patients with solid organ/ stem cell transplantation, patients on glucocorticoid therapy (at a dose of >/= 20 mg daily for >/= 14 days), or those on therapies that suppress B or T-cell responses – things like DMARDS and biological agents used to treat things like rheumatoid arthritis. It’s important to point out here that although patients with comorbidities like diabetes and heart disease and even patients that are elderly are relatively immunocompromised, but they are still usually infected with the same organisms that cause CAP in healthy adults and their treatment is actually covered in the current CAP guidelines.

Immunocompromised patients are usually infected with the same pathogens that cause CAP in the non-immunocompromised. Let me repeat that. Immunocompromised patients are usually infected with the same “core” pathogens that cause CAP in the non-immunocompromised. This includes strep pneumoniae, MSSA, H. influenzae, M. catarrhalis, and atypical bacteria. Therefore, immunocompromised patients admitted with CAP who do not have any additional risk factors for drug resistant bacteria should receive initial empiric antibiotics that are discussed in the IDSA CAP guidelines- antibiotics such as ceftriaxone + azithromycin.

That being said, there are other pathogens besides theses “core” pathogens that can cause CAP in the immunocompromised. These include ESBL-producing organisms, pseudomonas, MRSA, viruses like CMV or HSV, and even fungi like PJP and aspergillus. Each different type of immunocompromising condition will predispose patients to a different possible pathogen, but initial empiric therapy against these additional pathogens is only be necessary in select patients presenting with specific clinical or immunological risk factors.

So which immunocompromised patients with CAP should receive antibiotics that cover these resistant or opportunistic infections? The authors specifically say that initial empiric therapy that extends out beyond the “core” CAP pathogens should be given to patients in whom a resistant bacteria or opportunistic infection is suspected on the basis of risk factors and findings on examination, lab results, or imaging and in whom the delay in empiric antibiotic therapy will put the patient at an increased risk of death. To me, this means that patients with more severe disease, like those who are admitted to an ICU, or those who are intubated or on vasopressors, for example, can be used as a threshold to start broader antibiotic therapy tailored to their specific risk factors with rapid de-escalation if no resistant pathogen is identified.

This guideline then goes on to discuss the need for empiric therapy and the treatment for specific organisms. In regards to MRSA, they recommend covering for this pathogen if patients have a history of infection or colonization with MRSA in the previous 12 months. If your patient has multiple risk factors such as prior antibiotic use, recent hospitalization, or hemodialysis, for example, with a severe CAP it would not be unreasonable to cover MRSA with de-escalation with a negative MRSA nasal swab.

In regards to covering resistant GNB such as pseudomonas, the authors suggest covering if there is a history of colonization or infection with one of these organisms in the last 12 months, if there was a previous hospitalization with broad-spectrum antibiotic use, or if patients have a tracheostomy, neutropenia, or a history of pulmonary comorbidities such as bronchiectasis or cystic fibrosis. They also discuss coverage of multidrug- resistant organisms, PJP, nocardia, viruses, TB, and parasites- but I won’t bore you with these details. Please review the guidelines for more information about these much rarer circumstances.

In conclusion, just because your patient is “immunocompromised” does not necessarily mean you have to give them vancomycin plus Zosyn in the ER. Actually, most of the time they are adequately covered with ceftriaxone + azithromycin/ doxycycline (which is our typical CAP antibiotic regimen). If they have a severe pneumonia, require ICU admission, have several risk factors for resistant or opportunistic infections and have laboratory/clinical/ or imaging findings that suggest other organisms are involved- then we can broaden out our initial antibiotic choice.

As always, thank you so much for your time. You can take a deeper dive into the guideline by reading it on one of my favorite apps: Read by QxMD- the link to the guideline will be posted on the Show Notes. Also, we’ve now added closed captions on our YouTube page. Please subscribe to the channel by searching “ER-Rx.”