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Few groups investigate on Pneumocystis in normal infants around the world. Studies by us and others have documented that the primary infection by Pneumocystis is likely the most frequent, consistent, and stronglyagedependent respiratory infection occurring during the first year of life. This proposal gathers research teams from 7 different countries aiming to confirm the epidemiology of this mild infection in different geographical locations, and to characterize, or discard, its potential role in airway disease of immunocompetent infants. Lung pathology consisting of increased mucus associated to Pneumocystis in infant autopsied lungs has recently been shown, and this evidence is strongly supported by animal studies showing airway mucus increase and remodelling, and that Pneumocystis induces a strong immune response in the immunocompetent host. Importantly, the prevalence of this asymptomatic infection peaks between 2 and 5 months of age, which is the ageperiod window when infant respiratory morbidity and mortality increase. The lack of a culture method for routine microbiology diagnosis has importantly hampered research and recognition of this infection.

The proposed work will

• Confirm the epidemiology and prevalence of the Pneumocystis primary infection in healthy infants from 1 to 6 months of age in different geographical locations.
• Study, in a second country, the incidence of Pneumocystis in aborted fetuses to confirm vertical transmission, and describe the prevalence o f Pneumocystis in prematures up to 32 weeks of gestation.
• Describe the potential association of Pneumocystis with respiratory morbidity in hospitalized infants up to the age of 6 months by gathering the epidemiologic expertise of the team involved in this proposal in the analysis of cohort studies conducted in Chile as part of previous projects.
• Compare and select most recommendable diagnostic tools from available tools like serum betaglucan levels, immunofluorescence of nasopharyngeal aspirates, nPCR, and the new PCR recently developed by one of us.
• Innovate in noninvasive diagnosis by trying to identify volatile organic compounds (VOC) patterns associated to Pneumocystis in the espired air of hospitalized premature infants. This novel technique might permit an improved management of these patients by providing early and non invasive diagnosis, and avoiding unnecesary treatment. VOC will be also tested in other fungal respiratoryinfections as available.
• Describe the pulmonary microbiome patterns (bacterial and fungal) associated with Pneumocystis and the host activated genes response, by utilizing massive sequencing techniques (metagenomics and transcriptomics) in autopsy lung samples from otherwise healthy infants dying in the community.

In summary, this proposal will uncover the magnitude of this currentlyunrecognized infection of infancy, and reveal the need to diagnose it. Results will add to the increasing evidence of Pneumocystis high prevalence and involvement in respiratory morbidity of premature and normal infants during the age range between 2 to 5 months; a concept underscored by pathological effects documented in animal models. Therefore, the joint effort resulting from this proposal will recognize Pneumocystisassociated morbidity in prematures and infants and strengthen the need to diagnose this infection, and will promote well being by improving noninvasive diagnosis, and recognizing target infant groups at risk of increased respiratory morbidity resulting from Pneumocystis infection.