Pneumonia in immunocompromised patients is often caused by unusual or opportunistic pathogens that would otherwise have limited virulence in immunocompetent people, in addition to typical pathogens that cause pneumonia in immunocompetent patients but manifests as more severe infection. Symptoms and signs depend on the pathogen and on the predisposing factors or underlying conditions compromising the immune system. Diagnosis is based on extensive microbiological sampling often involving bronchoscopy, bronchoalveolar lavage, or a lung biopsy. Molecular diagnostics (eg, polymerase chain reaction) are preferred confirmatory tests. Because of the variety of possible pathogens, identifying an etiology early is important. Treatment depends on the underlying immune system defect and the pathogen.
The list of potential pathogens in patients with compromised immune system defenses is highly varied. Pathogens include those that cause community-acquired pneumonia as well as atypical or otherwise unusual pathogens (ie, the pathogen spectrum is broader than in immunocompetent patients) (1). More than one pathogen may be involved. Likely pathogens depend on the type of underlying defect in immune system defenses (see table ). However, respiratory symptoms and changes on chest imaging in immunocompromised patients may be due to various processes other than (or in addition to) infection, such as pulmonary hemorrhage, pulmonary edema, radiation injury, pulmonary toxicity due to cytotoxic drugs or immunotherapy, and tumor infiltrates.
Pneumonia in Immunocompromised Patients
Immune System Defect | Examples of Disorders Or Therapy With Defect* | Likely Pathogens |
|---|---|---|
Defective polymorphonuclear leukocytes | ||
Neutropenia | Acute leukemia, aplastic anemia, cancer chemotherapy | Gram-negative bacteria (eg, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) Staphylococcus aureus Aspergillus Candida |
Defective chemotaxis | S. aureus Gram-negative aerobic bacteria (eg, Klebsiella pneumoniae, Pseudomonas aeruginosa, Burkholderia cepacia) | |
Defective intracellular killing | Chronic granulomatous disease | S. aureus |
Defects in the alternative complement pathway (eg, properdin, factor D, factor B) | Neisseria species, including N. meningitidis and N. gonorrhoeae Streptococcus pneumoniae Haemophilus influenzae | |
C5 deficiency of the complement pathway | Congenital disorder | Gram-negative bacteria (especially Neisseria species, including N. meningitidis and N. gonorrhoeae) S. pneumoniae S. aureus |
Cell-mediated immunity | ||
T-cell deficiency or dysfunction | Hodgkin lymphoma, cancer chemotherapy, glucocorticoid therapy | Mycobacteria Viruses (eg, herpes simplex virus, cytomegalovirus) Strongyloides species Opportunistic fungi (eg, Aspergillus, Mucor, Cryptococcus species) Nocardia species Toxoplasma species |
T helper cell defects (eg, CD4+ T cells) | Advanced HIV disease (stage 3 HIV) | Pneumocystis jirovecii Toxoplasma species Cytomegalovirus Herpes simplex virus Human herpesvirus type 8 (manifesting as Kaposi sarcoma) Opportunistic fungi (eg, Aspergillus, Mucor, Cryptococcus species) Mycobacteria Opportunistic infections† |
Humoral immunodeficiency | ||
B-cell deficiency or dysfunction | Agammaglobulinemia, hematologic malignancies, HIV infection, nephrotic syndrome, impaired splenic function, congenital disorders such as common variable immune deficiency Chemotherapy, some immunomodulatory biologic therapies, chimeric antigen receptor-modified T (CAR-T) cell therapy, organ transplantation | S. pneumoniae H. influenzae Neisseria meningitidis |
Selective deficiency: IgA, IgG, IgM | S. pneumoniae H. influenzae Moraxella catarrhalis | |
Hypogammaglobulinemia | P. jirovecii Cytomegalovirus S. pneumoniae H. influenzae | |
* Examples. Many disorders cause multiple defects. | ||
† See also . | ||
General reference
1. Cheng GS, Crothers K, Aliberti S, et al. Immunocompromised Host Pneumonia: Definitions and Diagnostic Criteria: An Official American Thoracic Society Workshop Report. Ann Am Thorac Soc. 2023;20(3):341-353. doi:10.1513/AnnalsATS.202212-1019ST
Symptoms and Signs of Pneumonia in Immunocompromised Patients
Symptoms and signs may be the same as those that occur with community-acquired pneumonia in immunocompetent patients. Symptoms may include malaise, chills, fever, rigor, cough, dyspnea, and chest pain. However, immunocompromised patients may have no fever or respiratory signs and are less likely to have purulent sputum if they are neutropenic. In some patients, the only sign is fever. Symptoms and signs may become more prominent with reconstitution of the immune system and the host response to the pathogen. Disseminated infections are not uncommon; therefore, the clinical assessment should include looking for extra-pulmonary manifestations in the skin, central nervous system, and other organ systems.
Pearls & Pitfalls
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Diagnosis of Pneumonia in Immunocompromised Patients
Chest imaging
Assessment of oxygenation
Sputum induction or bronchoscopy to obtain lower respiratory samples
Blood cultures and molecular assays
Pathogens predicted based on symptoms, radiographic changes, and type of immunodeficiency
The diagnosis of pneumonia in immunocompromised patients is generally suspected first based on clinical presentation and confirmed based on a stepwise diagnostic approach, beginning with rapid noninvasive tests (eg, imaging, expectorated sputum testing) and progressing to more definitive and sometimes invasive procedures (eg, blood culture, bronchoscopic tissue or sputum examination, polymerase chain reaction [PCR]) when initial testing is unrevealing (1, 2).
Chest imaging and assessment of oxygenation (usually by pulse oximetry) are done in immunocompromised patients with respiratory symptoms or signs, or fever. If an infiltrate or hypoxemia is present on a chest radiograph more specific diagnostic assessment should be performed. Chest radiographs may be normal in Pneumocystis jirovecii pneumonia, but hypoxia or hypoxemia (an increased alveolar-arterial oxygen gradient on arterial blood gas testing) is usually present. If clinical suspicion of pneumonia is high and the chest radiograph is unrevealing, a chest CT scan should be performed (as lung infiltrates may not be apparent on chest radiography in immunocompromised patients).
Pathogen identification
Sputum testing and blood cultures are typically performed. Sputum testing should include Gram stain, mycobacterial and fungal stains and cultures, and sometimes testing for viruses (eg, PCR for cytomegalovirus DNA in a patient who has had a transplant or in a patient with HIV). If signs, symptoms, or risk factors for Aspergillus infection are present, serum galactomannan assay should be done.
It is important to aggressively pursue a microbiological diagnosis with induced sputum, bronchoscopy, or both, especially in patients with severe defects in immune function or failure to respond to broad-spectrum antibiotics. Lung biopsy should be considered when these tests do not provide a specific diagnosis and empiric therapy is not effective.
Molecular diagnostic techniques such as nucleic acid amplification tests (which includes PCR) play a critical role in pathogen identification; they are used to detect pathogen-specific nucleic acids or antigens.
Likely pathogens can also often be predicted based on symptoms, radiographic changes, and the type of immunodeficiency. In patients with acute symptoms, the differential diagnosis includes bacterial infection, hemorrhage, pulmonary edema, a leukocyte agglutinin reaction to transfusion of blood products, and pulmonary emboli. An indolent time course is more suggestive of a fungal or mycobacterial infection, an opportunistic viral infection, P. jirovecii pneumonia, a tumor, a cytotoxic drug reaction, or radiation injury.
Radiographs showing a localized opacity or consolidation usually indicate an infection involving bacteria (including Nocardia), mycobacteria, or fungi.
A diffuse interstitial pattern is more likely to represent a viral infection, P. jirovecii pneumonia, drug or radiation injury, or pulmonary edema.
Diffuse nodular lesions suggest mycobacteria, Nocardia species, fungi, or a tumor.
Cavitary disease suggests mycobacteria, Nocardia species, fungi, or bacteria, particularly S. aureus or anaerobes.
In organ or bone marrow transplantation recipients with bilateral interstitial pneumonia, the usual cause is cytomegalovirus, or the disease is idiopathic.
A pleural-based consolidation is suggestive of Aspergillus infection.
In patients with advanced HIV, bilateral pneumonia is usually P. jirovecii pneumonia. Many patients with HIV infection have P. jirovecii pneumonia as the initial advanced HIV-defining diagnosis, especially if they are not receiving antiretroviral therapy (ART). Patients with HIV infection who are not on antiretroviral therapy are at high risk for developing this pneumonia if prophylaxis is not given. Patients with HIV infection become vulnerable to P. jirovecii pneumonia when the CD4+ T cell count is < 200 cells/microliter.
Diagnosis references
1. Miller JM, Binnicker MJ, Campbell S, et al. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). Clin Infect Dis. 2024; Mar 5:ciae104. Published online March 5, 2024. doi:10.1093/cid/ciae104
2. Ramirez JA. General Approach to Immunocompromised Patients with Pneumonia: Insights from the Latest Consensus Documents. Semin Respir Crit Care Med. Published online October 24, 2025. doi:10.1055/a-2709-6182
Treatment of Pneumonia in Immunocompromised Patients
Broad-spectrum antimicrobial therapy
The antimicrobial therapy depends on the underlying immune system defect and the risk factors for specific pathogens (1, 2). Consultation with an infectious diseases specialist is usually indicated. In patients with neutropenia, empiric treatment depends on its underlying cause, radiographic findings, and severity of illness.
Generally, broad-spectrum antibiotics that are effective against gram-negative bacilli (especially Pseudomonas species), Staphylococcus aureus (including methicillin-resistant S. aureus [MRSA]), and anaerobes are needed, as for hospital-acquired pneumonia. If patients with conditions other than HIV infection do not improve with 5 days of antibiotic therapy, antifungal therapy is frequently added empirically.
Treatment references
1. Ramirez JA. General Approach to Immunocompromised Patients with Pneumonia: Insights from the Latest Consensus Documents. Semin Respir Crit Care Med. Published online October 24, 2025. doi:10.1055/a-2709-6182
2. Ramirez JA, Musher DM, Evans SE, et al. Treatment of Community-Acquired Pneumonia in Immunocompromised Adults: A Consensus Statement Regarding Initial Strategies. Chest. 2020;158(5):1896-1911. doi:10.1016/j.chest.2020.05.598
Prevention of Pneumonia in Immunocompromised Patients
Therapies to correct the underlying immune system defect or enhance its function are indicated for the prevention of pneumonia in immunocompromised patients. For example, patients with chemotherapy-induced neutropenia should receive granulocyte-colony stimulating factor (G-CSF, or filgrastim), and patients with hypogammaglobulinemia due to an inherited or acquired disease (eg, multiple myeloma, leukemia) should receive IV immune globulin.
Patients with HIV and CD4+ T cell count < 200 cells/microliter should receive daily prophylactic therapy with sulfamethoxazole/trimethoprim or other appropriate therapy (see prevention of Pneumocystis jirovecii pneumonia).
Vaccination is critical in such patients. For example, patients at risk of pneumonia with encapsulated bacteria (eg, hypogammaglobulinemia, asplenia) should receive vaccinations against pneumococcus and H. influenzae.
Key Points
Consider typical as well as unusual pathogens in immunocompromised patients who have pneumonia.
If patients have hypoxemia or an abnormal chest radiographs, perform further testing, including obtaining lower respiratory samples, either from induced sputum or bronchoscopically.
Begin with broad-spectrum antimicrobial therapy.
Drug Information for the Topic
