Pneumocystis jirovecii colonisation may occur among cystic fibrosis (CF) patients because of their underlying pulmonary disease. A wide epidemiological analysis was performed among CF patients from Spain to assess the prevalence of P. jirovecii colonisation and the distribution of different genotypes. P. jirovecii was identified by nested PCR targeting the mitochondrial large-subunit rRNA gene from sputum samples or oropharyngeal washes. The genotype was determined by direct sequencing. The prevalence of P. jirovecii colonisation among 88 consecutive CF patients was 21.5%. The polymorphisms identified were 85C/248C (45.4%), 85T/248C (27.2%) and 85A/248C (18.1%); in one case, a mix of genotypes was found. Colonisation was more frequent in subjects aged < 18 years (25.5% vs. 15.1%). Among the patients studied, 20.8% received treatment with azithromycin; all of these patients were colonised with P. jirovecii, but none developed Pneumocystis pneumonia (PcP) during a 1-year follow-up period. Concordance in the colonisation status of siblings suggested a common source of infection or person-to-person transmission.

Although asymptomatic carriers of Pneumocystis jirovecii with cystic fibrosis (CF) have been described previously, the molecular epidemiology of P. jirovecii in CF patients has not yet been clarified. This study identified the distribution and dynamic evolution of P. jirovecii genotypes based on the mitochondrial large-subunit (mt LSU) rRNA gene. The mt LSU rRNA genotypes of P. jirovecii isolates in 33 respiratory samples from CF patients were investigated using nested PCR and direct sequencing. Three different genotypes were detected: 36.3% genotype 1 (85C/248C); 15.1% genotype 2 (85A/248C); 42.4% genotype 3 (85T/248C); and 6% mixed genotypes. Patients studied during a 1-year follow-up period showed a continuous colonisation/clearance cycle involving P. jirovecii and an accumulative tendency to be colonised with genotype 3.

Pneumocystis jirovecii is an atypical opportunistic fungus with lung tropism and worldwide distribution that causes pneumonia in immunosuppressed individuals. The development of sensitive molecular techniques has led to the recognition of a colonization or carrier state of P. jirovecii, in which low levels of the organism are detected in persons who do not have pneumonia. Pneumocystis colonization has been described in individuals with various lung diseases, and accumulating evidence suggests that it may be a relevant issue with potential clinical impact. Only a few published studies carried out in Europe have evaluated the prevalence of Pneumocystis colonization in patients with cystic fibrosis, reporting ranges from 1.3-21.6%. The evolution of P. jirovecii colonization in cystic fibrosis patients is largely unknown. In a longitudinal study, none of the colonized patients developed pneumonia during a 1-year follow-up. Since patients with cystic fibrosis could act as major reservoirs and sources of infection for susceptible individuals further research is thus warranted to assess the true scope of the problem and to design rational preventive strategies if necessary. Moreover, it's necessary to elucidate the role of P. jirovecii infection in the natural history of cystic fibrosis in order to improve the clinical management of this disease.

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