Park JW, et al. - A total of 28,292 treatment episodes with prolonged (≥ 4 weeks), non-high-dose steroids over a 14-year period were involved to examine the incidence of pneumocystis pneumonia (PCP, a potentially life-threatening infectious disease that mainly occurs in immunocompromised hosts) and its risk factors in individuals with rheumatic disease receiving non-high-dose steroid treatment, along with the risks and advantages of PCP prophylaxis. In 1018.0 person-years, five PCP cases occurred particularly in the control group. The most important risk factors for PCP were concomitant steroid-pulse treatment and baseline lymphopenia. Treatment episodes with at least one of these factors exhibited higher 1-year PCP incidence rate, while no PCP befell in other treatment episodes. In the high-risk subgroup, trimethoprim-sulfamethoxazole (TMP-SMX) numerically decreased the risk. The number required to treat with TMP-SMX to arrest one PCP in the high-risk subgroup was lesser than the number demanded to harm by serious ADR. Thus, in individuals with rheumatic diseases getting prolonged, medium-dose steroids, the incidence of PCP depends on the presence of risk factors. Prophylactic TMP-SMX may have greater advantages than the potential risk in the high-risk subgroup.