Microbiology Case Study: An Adult Male with HIV Presents with Shortness of Breath

Case History

An adult male presented to the Emergency Department with hemoptysis and shortness of breath. The patient was previously diagnosed with HIV-1, but was non-compliant on antiretroviral medications. At the time of admission, HIV-1 viral load was greater than 1,000,000 copies/mL and his CD4 T⁺ cell count was 3 cells/µL. The following microbiology tests were ordered and were negative: acid fast bacilli culture, fungal culture, and Mycobacterium tuberculosis complex PCR on sputum as well as a Legionella urinary antigen. A bronchoalveolar lavage (BAL) was obtained and sent for a laboratory-developed Pneumocystis jirovecii PCR, which was positive.

Pneumocystis jirovecii

Previously named Pneumocystis carinii, Pneumocystis jirovecii was originally thought to be a parasite. Although this organism cannot be grown in routine fungal culture, molecular analysis has revealed that Pneumocystis is a fungus. Asymptomatic colonization is common, which may play a role in transmission or in disease development when the immune system is suppressed. Colonization is more common in children than adults.

Pneumocystis jirovecii is the causative agent of Pneumocystis jirovecii pneumonia (PJP or PCP). Patients with PJP often present with cough, fevers, and dyspnea. Diffuse bilateral infiltrates are commonly observed on chest X-rays. Patients are typically treated with trimethoprim-sulfamethoxazole, which is also used for PJP prophylaxis in high risk populations. Pneumocystis can very rarely infect extrapulmonary sites, including lymph nodes, spleen, bone marrow, and liver.

Any immunosuppressed person is at risk for PJP. In particular, patients with HIV and AIDS are at a high risk for PJP, especially those with a CD4⁺ T cell count less than 200 cells/µL. Prior to effective antiretroviral medications and routine PJP prophylaxis in AIDS patients, PJP was one of the top causes of infections and death in those with HIV and AIDS. In the highlighted case, our patient had a CD4 T⁺ cell count of 3 cells/µL, which put him in the high risk category.

When PJP is suspected, a respiratory sample, either BAL or induced sputum, should be collected. The gold standard is to perform microscopy on respiratory samples using histopathology stains (Grocott-Gomori methenamine silver (GMS), hematoxylin and eosin (H&E), Papanicolaou-stained, or immunohistochemistry) and microbiology stains (calcofluor white stain). On GMS stains, Pneumocystis appears as thin-walled spheres measuring 2 – 5 microns with intracystic bodies while foamy eosinophilic exudates can be observed on the H&E stain. In the microbiology lab, fluorescein-conjugated monoclonal antibody kits are often used, which can stain the cyst and/or trophic form of Pneumocystis, depending on the kit. However, the immunofluorescent stain lacks sensitivity, especially in the non-HIV population. Molecular assays have been developed, but are not widely available or standardized. In comparison to fluorescent stains, molecular assays are highly sensitive and specific for Pneumocystis DNA, but important caveats do exist. There are no FDA-cleared Pneumocystis PCR assays, meaning that methodology, and subsequent sensitivity and specificity, varies lab to lab. While not available yet, the development and use of quantitative PJP assays have been proposed, which could offer fungal burden information and help distinguish between colonization and infection. Serology options are available, but are not specific to PJP. One serological test, (1,3)-β-D-glucan (BDG), can be used as an aid for diagnosis of PJP. BDG is estimated to be 94-96% sensitive in PJP patients. While BDG testing is non-invasive, it is positive for a variety of fungal infections including Candida spp. and Aspergillus spp. Thus, additional PJP studies are needed to support a PJP diagnosis.

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-Paige M.K. Larkin, PhD, D(ABMM), M(ASCP)^CM is the Director of Molecular Microbiology and Associate Director of Clinical Microbiology at NorthShore University HealthSystem in Evanston, IL. Her interests include mycology, mycobacteriology, point-of-care testing, and molecular diagnostics, especially next generation sequencing.