Introduction: The incidence of pneumocystis pneumonia (PCP) in patients without human immunodeficiency virus infection (non-HIV) has increased and reported a higher mortality rate. Few reports have addressed the time to start treatment contributes to mortality.

Objective: To clarify the difference in mortality with non-HIV PCP by dividing the time to treatment initiation into early and late stages.

Methods: We included patients with non-HIV-PCP whose treatment was started within one week from hospital admission at three tertiary care hospitals in Japan between June 2006 and March 2021. The early and late-treatment groups were defined as patients treated within two days and after the third day of hospitalization. The primary endpoint was 30-day survival, and the secondary endpoint was 180-day survival. Patient backgrounds were adjusted using the overlap weighting with propensity score method.

Results: Data from a total of 141 patients were included, 97 in the early-treatment group and 44 in the late-treatment group. Univariate analysis showed no significant differences between the early and late-treatment groups in 30-day mortality (11.3% vs. 11.4%, p = 1.000) and 180-day mortality (18.6% vs. 25.0%, p = 0.514). There were no significant differences in 30-day mortality (12.8% vs. 10.4%, p = 0.680) or 180-day mortality (20.2% vs. 22.3%, p = 0.781) after adjustment for confounding factors.

Conclusions: In this study, the analysis showed no difference in prognosis between the early and late-treatment groups after adjusting for patient background.