Introduction Outbreaks of Saharan dust have been shown to exacerbate the effect of particulate matter (PM) on mortality. Their role on PM–morbidity association is less clear. This study aims to evaluate the effect of Saharan dust on the PM–hospitalisations association in Rome, Italy.

Methods We studied residents hospitalised in Rome between 2001 and 2004 and performed a time-series analysis to explore the effects of PM_2.5, PM_2.5–10 and PM₁₀ on cardiac, cerebrovascular and respiratory emergency hospitalisations, respectively. Saharan dust days were identified by combining Light Detection and Ranging observations and analyses from operational models. We tested a dust–PM interaction to evaluate the hypothesis that the PM effect on hospitalisations would be enhanced on dust days.

Results We studied 77 354, 26 557 and 31 620 hospitalisations for cardiac, cerebrovascular and respiratory diseases, respectively, providing effect estimates per IQR. PM_2.5–10 was associated with cardiac diseases (3.93%; 95% CI 1.58 to 6.34). PM₁₀ was associated with cardiac (3.37%; 95% CI 1.11 to 5.68), cerebrovascular (2.64%; 95% CI 0.06 to 5.29) and respiratory diseases (3.59%: 95% CI 0.18 to 7.12). No effect of PM_2.5 was detected. Saharan dust modified the effect of the PM_2.5–10 on respiratory hospitalisations, higher during dust days compared with dust-free days (14.63% vs −0.32%; p value of interaction=0.006). Saharan dust also increased the effect of PM₁₀ on cerebrovascular diseases (5.04% vs 0.90%, p value of interaction=0.143).

Discussion A clear enhanced effect of PM_2.5–10 on respiratory diseases and of PM₁₀ on cerebrovascular diseases emerged during Saharan dust outbreaks.