What is Pneumocystis pneumonia (PJP)
PJP is caused by Pneumocystis jirovecii, which is an ascomycetous fungal pathogen.1,2 Pneumocystis jirovecii, formerly known as Pneumocystis carinii, is an opportunistic fungal pathogen that can cause life-threatening cases of PJP in immunocompromised or critically ill patients.1,2
Pathogenesis
Pneumocystis jirovecii can colonise healthy individuals; acquired from person-to-person transmission through the air.1 PJP grows slowly and noninvasively in its permissive host and rarely spreads beyond the lungs, but extrapulmonary PJP may occasionally occur in immunocompromised people.2
Epidemiology
The global incidence of PJP is estimated to be approximately 500,000 cases per year (in patients with and without acquired immune deficiency syndrome).3 The human immunodeficiency virus (HIV) epidemic of the 1980s contributed to an increase in cases of PJP.4 After the discovery of antiretroviral therapy and trimethoprim-sulfamethoxazole, cases of PJP in patients with HIV decreased in high-income countries.4 However, PJP cases in patients without HIV have been on the rise due to increasing blood and organ transplants and the advent of new, more potent immunotherapies.4
The incidence of PJP has increased over the past 15 years in patients with other predisposing immunodeficiencies, particularly transplant recipients.5 The impact of PJP on morbidity and mortality of immunocompromised patients is substantial, with up to 40% of patients with acute lymphoblastic leukaemia affected.6
Hospital survival rate of PJP ranges from 7 to 20% in HIV-positive patients, and from 29 to 60% in HIV-negative patients.4 In the absence of treatment, the mortality rate of PJP is nearly 100% in patients with weakened immune systems.7
Risk factors
Known risk factors for PJP include:4,7
- HIV infection
- Haematological and oncological malignancies
- Stem cell transplantation
- Solid organ transplantation
- Immunosuppressant drugs
- Long-term use of corticosteroid therapy
- Connective tissue diseases
Pathogenic species
PJP is caused by the ascomycetous fungal pathogen, Pneumocystis, which was originally thought to be a protozoa.2
References
- WHO fungal priority pathogens list to guide research, development and public health action. Geneva: World Health Organization. Available at: https://www.who.int/publications/i/item/9789240060241. Accessed July 2023.
- Gigliotti F, Limper AH and Wright T. Cold Spring Harb Perspect Med. 2014;4:a019828.
- Bongomin F et al. J Fungi (Basel). 2017;3:57.
- Bateman M, Oladele R and Kolls JK. Med Mycol. 2020;58:1015–1028.
- Iriart X et al. J Fungi (Basel). 2015;1:293–331.
- Maschmeyer G et al. J Antimicrob Chemother. 2016;71:2405–2413.
- Zakrzewska M et al. Dev Period Med. 2019;23:159–162.