Pulmonary Disease in the Immunocompromised Patient

Introduction

Infection with the human immunodeficiency virus (HIV) that causes the acquired immunodeficiency syndrome (AIDS) has been and continues to be a serious health threat around the globe. Despite great advances in the treatment of HIV/AIDS, such as the aggressive use of prophylactic antimicrobial therapies and the introduction of highly effective antiretroviral therapies, it remains a major cause of morbidity and mortality in populations with limited access to care, such as in sub-Saharan Africa, Eastern Europe, and Central Asia.

Highly active antiretroviral therapy (HAART) has been associated with a dramatic reduction in HIV-associated morbidity and mortality among patients with access to this treatment. By suppressing viral replication, it decreases the viral load and increases the CD4 cell count. Patients receiving HAART have a reduced prevalence of opportunistic infections and certain neoplasms. However, restoration of the immune system in patients treated with antiretroviral therapy may sometimes result in the immune reconstitution inflammatory syndrome (IRIS), which can cause considerable morbidity. Moreover, ART itself is increasingly implicated as a cause of respiratory symptoms and disease, including nucleoside-induced lactic acidosis, an increased incidence of bacterial pneumonia, and hypersensitivity reactions.

In April 2014, the Centers for Disease Control and Prevention (CDC) revised the definition of HIV infection to address multiple issues, the most important of which was the need to adapt to recent changes in diagnostic criteria. Laboratory criteria for defining a confirmed case now accommodate new multitest algorithms, including criteria for differentiating between HIV-1 and HIV-2 infection and for recognizing early HIV infection. A confirmed case can be classified in one of five HIV infection stages (0, 1, 2, 3, or unknown); early infection, recognized by a negative HIV test within 6 months of HIV diagnosis, is classified as stage 0, and acquired immunodeficiency syndrome (AIDS) is classified as stage 3, when the immune system of a person infected with HIV becomes severely compromised (CD4 cell count <200 cells/µL) or the person becomes ill with an opportunistic infection. Criteria for stage 3 (AIDS) have been simplified by eliminating the need to differentiate between definitive and presumptive diagnoses of opportunistic illnesses. Stage 1 is defined as acute infection, a time during which large amounts of the virus are being produced, and is characterized by flulike symptoms. Stage 2 is defined as clinical latency during which the virus replicates at very low levels but is still active. During this stage, the patient may be asymptomatic and with proper treatment can live for decades. Without treatment, this period lasts on average 10 years, but some patients may progress faster.

There is considerable overlap in the imaging manifestations of the various pulmonary complications of HIV/AIDS. Furthermore, the chest radiograph may be normal even when pulmonary disease is present. However, by carefully correlating clinical, laboratory, and imaging data with results of sputum analysis, bronchoalveolar lavage, and transbronchial biopsy, a confident diagnosis can usually be made. Computed tomography (CT) is useful in diagnosis or exclusion of pulmonary complications when radiographs are normal. It is also helpful in limiting the differential diagnosis when radiography is abnormal.

Box 15.1 summarizes the respiratory disorders associated with HIV/AIDS.