Immune Response to P. jirovecii | CDC EID

EID Journal Home > Volume 15, Number 10–October 2009

Volume 15, Number 10–October 2009
Research
Healthcare Worker Occupation and Immune Response to Pneumocystis jirovecii
Renuka Tipirneni, Kieran R. Daly, Leah G. Jarlsberg, Judy V. Koch, Alexandra Swartzman, Brenna M. Roth, Peter D. Walzer, and Laurence Huang
Author affiliations: San Francisco General Hospital/University of California, San Francisco, California, USA (R. Tipirneni, L.G. Jarlsberg, A. Swartzman, B.M. Roth, L. Huang); and Veterans Affairs Medical Center/University of Cincinnati, Cincinnati, Ohio, USA (K.R. Daly, J.V. Koch, P.D. Walzer)

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Abstract
The reservoir and mode of transmission of Pneumocystis jirovecii remain uncertain. We conducted a cross-sectional study of 126 San Francisco General Hospital staff in clinical (n = 103) and nonclinical (n = 23) occupations to assess whether occupational exposure was associated with immune responses to P. jirovecii. We examined antibody levels by ELISA for 3 overlapping fragments that span the P. jirovecii major surface glycoprotein (Msg): MsgA, MsgB, and MsgC1. Clinical occupation participants had higher geometric mean antibody levels to MsgC1 than did nonclinical occupation participants (21.1 vs. 8.2, p = 0.004); clinical occupation was an independent predictor of higher MsgC1 antibody levels (parameter estimate = 0.89, 95% confidence interval 0.29–1.48, p = 0.003). In contrast, occupation was not significantly associated with antibody responses to either MsgA or MsgB. Healthcare workers may have occupational exposure to P. jirovecii. Humans may be a reservoir for P. jirovecii and may transmit it from person to person.

Although the incidence of Pneumocystis jirovecii pneumonia (PCP) has declined in the era of combination antiretroviral therapy, PCP remains the most common serious opportunistic infection among human immunodeficiency virus (HIV)-infected persons in the United States (1). The reservoir and mode of transmission of P. jirovecii remain uncertain because of an inability to grow the organism in vitro. However, studies of immune responses to P. jirovecii have provided important insights into its epidemiology, showing that up to 80%–100% of children have detectable P. jirovecii antibodies by 8 years of age (2–9). These findings suggest that P. jirovecii is ubiquitous, that humans are exposed to P. jirovecii early in life, and that PCP that develops later in life results from reactivation of latent infection.

Emerging evidence suggests that PCP also can result from recent acquisition of P. jirovecii, and the organism may be transmitted from person to person (10,11). In the hospital or clinic, numerous PCP outbreaks have been reported among immunocompromised patients who shared common healthcare workers (HCWs), hospital rooms, wards, or clinics (12–21). In the laboratory, animal-to-animal transmission of Pneumocystis spp. has been demonstrated both by immunocompromised and immunocompetent hosts after periods of exposure as short as 1 day (22,23). Dumoulin et al. demonstrated that immunocompetent mice became transiently colonized with Pneumocystis spp. after contact with Pneumocystis-infected mice and then were able to transmit the infection to Pneumocystis-free mice that had severe combined immunodeficiency (23).

Several studies have found that P. jirovecii can colonize immunocompetent humans and suggest that such persons may serve as potential reservoirs (24). The question that arises is whether person-to-person transmission occurs through immunocompetent hosts, such as HCWs, who may be transiently colonized with P. jirovecii during brief clinical interactions with PCP patients and subsequently transmit the infection to other immunocompromised patients. Prior studies involving HCWs used different specimens (e.g., induced sputum, oropharyngeal wash, nasal rinse, deep nasal swab, blood) and different laboratory methods (i.e., different PCR and ELISA) to compare exposed and unexposed groups, making findings difficult to compare across studies (25–31). In addition, these studies compared different groups of HCWs and did not include a control group without patient contact.

Therefore, we performed a cross-sectional study of hospital staff at San Francisco General Hospital (SFGH) in both clinical (exposed) and nonclinical (unexposed) occupations. Our goal was to determine whether HCW occupation was associated with antibody levels to P. jirovecii. Finding this association would suggest that HCWs may acquire P. jirovecii and potentially be a reservoir in the hospital setting.

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