Data on features of Pneumocystis primary infection in infancy are still fragmented. To study Pneumocystis primary infection, 192 infants who were monitored for acute pulmonary disease or fever over a 40-month period were retrospectively investigated. P. jirovecii detection on archival nasopharyngeal aspirates was performed using a qPCR assay. Factors associated with P. jirovecii were assessed using univariate and multivariate analyses. P. jirovecii genotypes in infants and a control group of adults contemporaneously diagnosed with Pneumocystis pneumonia were identified using unilocus, bilocus, and multilocus sequence typing (MLST). P. jirovecii was detected in 35 infants (18.2%). The univariate analysis pointed out four factors: viral infection (P =. 035, OR [IC 95], 2.2 [1.1-4.7]), lower respiratory tract infection (P =. 032, OR [IC 95], 2.5 [1.1-5.9]), absence of hospital discharge after birth (P =. 003, OR (IC 95), 0.1 (0.02-0.5]), and the 63-189-day group (P <. 001, OR [IC 95], 42.2 [5.4-332]). The multivariate analysis confirmed these two latter factors (P =. 02, OR [IC 95], 0.1 [0.02-0.72]; P =. 005, OR [IC 95], 11.5 [2.1-63.5]). Thus, P. jirovecii acquisition mostly takes place in the community. A comparison of these data with those of previously published studies showed that median and interquartile range of positive-infant ages were close to those observed in Chile, Denmark, and Peru, highlighting similar characteristics. Common unilocus or bilocus genotypes were identified in infants and adults, whereas no MLST genotypes were shared. Therefore, a common reservoir made up of infected infants and adults is still hypothetical. Finally, primary infection is a worldwide phenomenon occurring at the same time in childhood regardless of geographical location, rather than an incidental event.