Current Epidemiology of Pneumocystis Pneumonia Alison Morris,*† Jens D
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Current Epidemiology of Pneumocystis Pneumonia Alison Morris,*† Jens D. Lundgren,‡ Henry Masur,§ Peter D. Walzer,¶ Debra L. Hanson,# Toni Frederick,# Laurence Huang,** Charles B. Beard,†† and Jonathan E. Kaplan# Pneumocystis pneumonia (PCP) has historically been antiretroviral drugs remain at high risk, and PCP continues one of the leading causes of disease among persons with to develop in certain groups in industrialized countries. AIDS. The introduction of highly active antiretroviral thera- The drug of choice for treatment and chemoprophylax- py in industrialized nations has brought about dramatic is of PCP is trimethoprim-sulfamethoxazole (TMP-SMX). declines in the incidence of AIDS-associated complica- In recent years, antimicrobial drug resistance has emerged tions, including PCP. In the adult population, the incidence of PCP has significantly decreased, but it remains among as a possible cause of failure of patients to respond to the most common AIDS-defining infections. Similar TMP-SMX. Investigators have demonstrated an associa- declines have been documented in the pediatric popula- tion between exposure to sulfa drugs and mutations in the tion. In much of the developing world, PCP remains a sig- dihydropteroate synthase (DHPS) gene of P. jirovecii, but nificant health problem, although its incidence among the relationship between these mutations and treatment (or adults in sub-Saharan Africa has been debated. This prophylaxis) failure is unclear. Understanding whether review discusses the epidemiology of PCP during the cur- DHPS mutations cause antimicrobial drug resistance is rent era of the AIDS epidemic. Although fewer cases of important in guiding clinicians who care for patients with PCP occur in industrialized countries, increasing drug- PCP. resistant HIV infections, possible drug-resistant PCP, and the tremendous number of AIDS cases in developing A series of articles in this issue of Emerging Infectious countries make this disease of continued public health Diseases highlights the continuing importance of PCP, the importance. potential for drug resistance, and laboratory techniques that can be used to study the problem. We hope that these articles will stimulate interest in exploring the relationship neumocystis pneumonia (PCP), which is caused by between DHPS mutations and resistance of P. jirovecii to PPneumocystis jirovecii (formerly P. carinii f. sp. sulfa-containing drugs and in assessing DHPS mutations hominis), is frequently the first serious illness encountered as possible causes of treatment failure in patients with by HIV-infected persons. During the early years of the PCP. In this introductory article, we summarize the AIDS epidemic, PCP was the AIDS-defining illness for as changes in incidence of PCP since the introduction of many as two thirds of patients in the United States. HAART, discuss groups at risk for PCP in developing and Although a decline in incidence of PCP occurred during industrialized nations, and examine possible future trends the era of highly active antiretroviral therapy (HAART), in the disease. A data collection form has been included PCP remains the most common serious opportunistic ill- online with this series of articles to assist in the collection ness in HIV-infected persons (1). Patients in the develop- of appropriate and standardized data from patients with ing world without access to PCP prophylaxis or PCP and to facilitate comparing and pooling data from dif- ferent centers (online Appendix available from http:// *University of Southern California, Los Angeles, California, USA; www.cdc.gov/ncidod/eid/vol10no10/03-0985_ app.pdf). †University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; ‡University of Copenhagen, Hvidovre, Denmark; §National Institutes of Health, Bethesda, Maryland, PCP before HAART USA; ¶University of Cincinnati, Cincinnati, Ohio, USA; #Centers The first clinical cases of PCP were reported during for Disease Control and Prevention, Atlanta, Georgia, USA; World War II in orphanages in Europe. These cases of **University of California San Francisco, San Francisco, “plasma cell pneumonia” were common among malnour- California, USA; and ††Centers for Disease Control and Prevention, Fort Collins, Colorado, USA ished children and were later reported in children in Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 10, October 2004 1713 PERSPECTIVES Iranian orphanages. The disease was then recognized in per year from 1996 through 1998 (1). Despite this improve- patients who were immunocompromised because of ment, PCP is still the most common AIDS-defining oppor- malignancies, immunosuppressive therapy, or congenital tunistic infection in the United States. immunodeficiencies. Solid organ transplantation increased The Multicenter AIDS Cohort study (MACS) has fol- the number of patients at risk for PCP, although rates lowed >5,000 homosexual men since 1984 (6). Of these, diminished after chemoprophylaxis was introduced. 2,195 were either HIV-infected at time of enrollment or Without chemoprophylaxis, rates of PCP are 5%–25% in seroconverted to HIV during the study. Opportunistic transplant patients, 2%–6% in patients with collagen vas- infection rates were compared for the HAART era cular disease, and 1%–25% in patients with cancer. (1996–1998) and the era of antiretroviral monotherapy Defects in CD4+ lymphocytes are a primary risk factor for (1990–1992) (7). For persons who seroconverted during developing PCP, but the immune response to Pneumocystis the study period, the relative hazard for development of is complex. CD8+ lymphocytes seem to be important in PCP from seroconversion to initial AIDS-defining oppor- Pneumocystis clearance, and defects in B-cells and anti- tunistic infection was 0.06 during the HAART era com- body production may also predispose to PCP. pared to the time of monotherapy. For those already The beginning of the AIDS epidemic in the early 1980s diagnosed with AIDS, the study found a hazard of 0.16, shifted the incidence of PCP from a rare disease to a more which demonstrated a dramatically lower risk for PCP dur- common pneumonia. Clusters of PCP cases in homosexu- ing the HAART era. al men and intravenous drug users were one of the first In Europe, the EuroSIDA study has followed a cohort indications of the HIV epidemic (2). PCP rapidly became of >8,500 HIV-infected patients. The investigators exam- the leading AIDS-defining diagnosis in HIV-infected ined changes in incidence of AIDS-defining illnesses patients. In the initial stages of the epidemic, PCP rates before and after HAART was introduced and found results were as high as 20 per 100 person-years for those with similar to those in North America (8). PCP cases decreased CD4+ cell counts <200 cells/µL (3). PCP was responsible over time (1994–1998). Incidence of PCP fell from 4.9 for two thirds of AIDS-defining illnesses, and an estimat- cases per 100 person-years before March 1995 to 0.3 cases ed 75% of HIV-infected patients would develop PCP dur- per 100 person-years after March 1998 (9). ing their lifetime (4). The first substantial decline in the incidence of PCP Occurrence in Relation to PCP Prophylaxis occurred after the introduction of anti-Pneumocystis pro- PCP still occurs in industrialized nations despite the phylaxis in 1989 (5). Although absolute numbers of cases availability of HAART and anti-Pneumocystis prophylaxis. of PCP as an AIDS-defining illness in the United States remained stable from 1989 to 1992 because of an increas- ing incidence of AIDS, the percentage of AIDS cases with PCP declined from 53% in 1989 to 49%, 46%, and 42% in 1990, 1991, and 1992, respectively (Centers for Disease Control and Prevention, AIDS Surveillance Summaries, 1989–1992). The later use of combination antiretroviral therapy further reduced the rates of PCP among adults by 3.4% per year after 1992 (1). PCP in Adults in Industrialized Countries after HAART Incidence The advent of HAART has resulted in further declines in rates of PCP and other opportunistic infections (1). Several large, multicenter studies have specifically tracked the inci- dence and epidemiologic features of PCP. The largest is the Figure 1. Yearly opportunistic infection rates per 1,000 person- Adult and Adolescent Spectrum of HIV Disease (ASD) years, CDC Adult and Adolescent Spectrum of Disease Project, Project. Data from this project indicated a marked reduc- 1994–2001. CMV, cytomegalovirus; HAART, highly active anti- tion in the incidence of all opportunistic infections in 1996 retroviral therapy; KS, Kaposi’s sarcoma; MAC, Mycobacterium and 1997, when HAART first became widely available avium complex; PCP, Pneumocystis pneumonia. Data are stan- dardized to the population of AIDS cases reported nationally in the (Figure 1). PCP cases decreased 3.4% per year from 1992 same year by age, sex, race, HIV exposure mode, country of through 1995; the rate of decline of PCP increased to 21.5% origin, and CD4+ lymphocyte count. 1714 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 10, October 2004 Current Epidemiology of Pneumocystis Pneumonia ASD investigated the history of prescriptions for PCP pro- cell levels. ASD found that the median CD4+ cell count in phylaxis in HIV-infected adults in whom developed PCP persons with PCP while on HAART was extremely low from 1999 through 2001 (Figure 2). Almost 44% of PCP (29 cells/µL), although the count was somewhat higher cases occurred in patients not receiving medical care, most than for those not on HAART (13 cells/µL) (1).