Limited Asymptomatic Carriage ofPneumocystis jiroveciin Human Immunodeficiency Virus–Infected Patients

Abstract

Forty-seven bronchoalveolar lavage fluid samples from 16 human immunodeficiency virus (HIV)-infectedpatients were used to test the latency model of Pneumocystis infection in the human host. Identification of DNA sequence polymorphisms at 4 independent loci were used to genotype Pneumocystis jiroveci from the 35 samples that contained detectable P. jiroveci DNA. Eighteen of those 35 samples came from patients who did not have Pneumocystis pneumonia (PCP) and had confirmed alternative diagnoses. Seven patients had asymptomatic carriage of P. jiroveci over periods of р9.5 months after an episode of PCP, and in all 7 cases, a change in genotype from that in the original episode of PCP was observed. The absence of P. jiroveci DNA in one-fourth of the 47 samples and the observed changes in genotype during asymptomatic carriage do not support the latency model of infection. Asymptomatic carriage in HIV-infected patients may play a role in transmission of P. jiroveci and may even supply a reservoir for future infections.The route of transmission of human Pneumocystis infection is still not understood. It was long thought that Pneumocystis jiroveci organisms were acquired during childhood and persisted throughout life in the lungs in a dormant phase [1,2]. Subsequent immunosuppression of the host, resulting from a variety of causes, permitted the fungus to propagate and to cause disease. According to this theory of transmission, there was little reason to protect immunosuppressed adults from possible exposure to Pneumocystis; acquisition of the infection was thought to take place early in life and not at the time of immunosuppression. The latency hypothesis, however, has recently been challenged. Several studies have suggested that, in the immunocompetent human host, Pneumocystis organisms are frequently acquired and cleared by the immune system, rather than being acquired during childhood and persisting for a lifetime. This reinfection hypothesis has important public health implications, because it suggests that susceptible individuals could be protected from Pneumocystis infection.Data refuting the latency hypothesis come from animal studies. It has been shown in a rat model that Pneumocystis organisms were eliminated from the lungs after Pneumocystis pneumonia (PCP) and that persistence of latent organisms was limited [3]. Similar results have been obtained using the severe combined immunodeficiency (SCID) mouse model [4]. In addition, some studies of human infection have indicated the

Rising incidence of Pneumocystis jirovecii pneumonia suggests iatrogenic exposure of immune-compromised patients may be becoming a significant problem

“…As only those with suspected PCP were tested, this cohort might have been expected to have a higher colonization rate than average. The findings are at odds with reports of colonization rates of 10-46 % in both immune-compromised and immune-competent individuals (Vidal et al, 2006;Wakefield et al, 2003;Maskell et al, 2003;Mori et al, 2009). However, some of these results were based on nested protocols, which often suffer from poor specificity.…”

“…Additionally, its detection in hospital air samples up to 8 m from patients with confirmed infection also supports transmission from an infected patient (Choukri et al, 2010). Asymptomatic colonization is thought to be relatively common (Maskell et al, 2003;Wakefield et al, 2003;Vidal et al, 2006) and can progress to overt infection when a patient's immune status deteriorates (Mori et al, 2009). Co-attendance with other immune-compromised patients in health-care settings may, therefore, be a risk factor for colonization and a later overt infectious episode.…”

Etiología de la neumonía en pacientes chilenos infectados por el virus de la inmunodeficiencia humana

“…La RPC para P. jiroveci tuvo una sensibilidad cercana a 100%, tanto en esputo como LBA. La especifi cidad cayó debido a que algunos pacientes tuvieron un diagnóstico etiológico diferente y, por lo tanto, estaban colonizados por P. jiroveci, tal como ha sido extensamente descrito en la literatura médica [23][24][25][26] . Algunos de estos pacientes podrían desarrollar infección por P. jiroveci a futuro, según lo reportado por Elvin y cols 27 , quienes describieron que seis de ocho pacientes asintomáticos con una RPC positiva para P. jiroveci, desarrollaron neumonía por este agente entre los 164 y 352 días posteriores al resultado positivo del examen.…”

Pneumocystis jirovecii Infection

“…15 16 Limited asymptomatic carriage of Pneumocystis has been demonstrated in some HIV immunosuppressed adults; during carriage a change in genotype was observed, strongly supporting a hypothesis of ''recent infection''. 17 Further support for the ''recent infection'' model comes from studies of patients with recurrent episodes of Pneumocystis pneumonia in which a different genotype of Pneumocystis was associated with each episode. 18 19 Recent infection is suggested by the finding that allelic variation patterns in isolates of Pneumocystis are correlated with patient's place of diagnosis and not their place of birth.…”

“…It is further hypothesised that these groups of patients may be important in the person to person transmission of Pneumocystis and that they may be a reservoir for future Pneumocystis infection in other susceptible (immunosuppressed) individuals. 17 WHY RENAME PNEUMOCYSTIS CARINII?…”