ABSTRACT
As the AIDS epidemic continues its progression through U.S. society, the atrisk populations have changed, and the incidence is now growing fastest among medically underserved, African-American, and female populations [1-3]. In these populations, Pneumocystis pneumonia (PcP) remains a leading opportunistic infection [4,5]. In countries considered to be ‘‘developing,’’ (i.e., Africa, Asia, the Phillipines, and Central and South America), the number of those infected with HIV has increased dramatically, sometimes affecting one-third of the population in some sub-Saharan countries. Although PcP rarely occurred in African adults in the first decade of the AIDS pandemic, the incidence has risen dramatically, as it has in other developing countries, reaching a 25 to 80% coinfection rate with tuberculosis and a mortality rate ranging from 20 to 80% [5]. Moreover, PcP is occurring more frequently in transplant recipients, especially in lung transplant patients [6] and those receiving high-dose corticosteroids for brain neoplasms, inflammatory or collagen-vascular disorders, and especially those with Wegener’s granulomatosis [7]. Trimethoprim-Sulfamethoxazole (TMP-SMX) remains the most efficacious prophylaxis and therapy for PcP [8,9]. Approximately 50% of Pneumocystis jirovecii isolates from HIV patients in different geo-
graphic areas contained a double mutation in the DHPS gene, which was associated with sulfa resistance in other pathogens [10,11]. These data suggest that resistance to TMP-SMX in human PcP may be emerging. A person-to-person spread is suspected as the primary mode of transmission for human PcP. However, basic concepts-such as the role of nonimmunosuppressed hosts as potential reservoirs of infection or the length of time organisms are carried and remain infective-are not known. Such information is of vital importance to the susceptible patient. Without adequate data for understanding the transmission cycles of PcP, recommendations for standards of care, such as isolation procedures for patients, are of little value. In the present chapter, the current knowledge regarding the transmission and epidemiology of Pneumocystis is discussed in the context of both human studies and animal model experiments.
