In 2021, there were 103.76 million (95% UI: 102.13, 105.44 million) global population suffered from rIDPs, leading to 21.94 thousand (95% UI: 15.21, 26.89 thousand) associated deaths. The ASMR, age-standardized DALY rate, and age-standardized YLD rate of rIDPs were 0.30 per 100,000 population (95% UI: 0.21, 0.38 per 100,000 population), 58.44 per 100,000 population (95% UI: 42.92, 77.26 per 100,000 population), and 37.94 per 100,000 population (95% UI: 25.47, 54.88 per 100,000 population), respectively (Table 1 and Additional file 1: Table S4–S7). From 1990 to 2021, there were clear reductions in the global ASPR, age-standardized DALY rates, and age-standardized YLD rates, with AAPCs of − 0.28% (95% CI: − 0.32, − 0.25%), − 0.16% (95% CI: − 0.22, − 0.11%), and − 0.58% (95% CI: − 0.61, − 0.54%), respectively (Table 2 and Additional file 1: Tables S8–S12). In contrast, there were increased AAPCs in the global ASMR (0.53%, 95% CI: 0.46, 0.60%) and age-standardized YLL rate (AAPC: 0.77%, 95% CI: 0.67, 0.86%) during the same period (Additional file 1: Tables S8–S12).

The geographic distribution showed that in 2021, the disease burden of rIDPs was dominated in sub-Saharan Africa and South Asia with age-standardized DALY rates of 126.35 per 100,000 population (95% UI: 91.04, 161.73 per 100,000 population) and 80.80 per 100,000 population (95% UI: 57.31, 114.10 per 100,000 population), respectively (Table 1). The two regions also showed less reductions in age-standardized DALY rates compared to other regions (AAPC in sub-Saharan Africa: − 0.30%, 95% CI: − 0.35, − 0.24% and South Asia: − 0.90%, 95% CI: − 0.92, − 0.87%) between 1990 and 2021. Among the most suffered countries and territories, Burkina Faso (243.16 per 100,000 population, 95% UI: 165.42, 337.39 per 100,000 population), Chad (229.10 per 100,000 population, 95% UI: 161.25, 336.69 per 100,000 population), and Gambia (227.39 per 100,000 population, 95% UI: 139.52, 327.70 per 100,000 population) accounted for the highest age-standardized DALY rates in 2021. For age-standardized YLD rates, Yemen (126.81 per 100,000 population, 95% UI: 87.86, 174.23 per 100,000 population), Mali (100.75 per 100,000 population, 95% UI: 66.18, 144.78 per 100,000 population), and Bhutan (94.47 per 100,000 population, 95% UI: 56.26, 140.72 per 100,000 population) accounted for the highest burden among countries and territories (Fig. 1). The global distributions of ASPR, ASMR, and age-standardized YLL rates are also shown in Additional file 1: Table S13. The AAPCs of 204 countries and territories between 1990 and 2021 can be found in Additional file 1: Table S14.

Age-standardized DALY and YLD rates (per 100,000 population) of rIDPs by countries and territories, in 2021. (A Age-standardized DALY rates of rIDPs. B Age-standardized YLD rates of rIDPs). The colors indicate the SDI levels of countries and territories. The black lines with capital letters indicate the GBD super regions for countries and territories. Countries and territories were abbreviated by ISO-3 code, and the full names can be found in Additional file 2. DALY disability-adjusted life-year; YLD year lived with disability; rIDP rare infectious disease of poverty

For countries, territories, and regions with different SDI values, the ASPRs, ASMRs, age-standardized DALY, YLD, and YLL rates were negatively associated with SDI values (Fig. 2 and Additional file 1: Fig. S1–S3). In 2021, the age-standardized DALY rate in low SDI regions was 120.00 per 100,000 population (95% UI: 88.43, 153.30 per 100,000 population). In comparison, the value was 7.40 per 100,000 population (95% UI: 5.31, 10.44 per 100,000 population) in high SDI regions. There were also inverse relationships between temporal changes in the rIDPs burden metrics and SDI values. The temporal-spatial distributions of disease burden for rIDPs by SDI levels are shown in Fig. 3 and Additional file 1: Fig. S4. Low SDI regions also had the least reduction in AAPC of age-standardized DALY rate (− 0.40%, 95% CI: − 0.47, − 0.33%), compared to the largest AAPC reduction in high-middle SDI regions (− 1.99%, 95% CI: − 2.07, − 1.90%). Despite an overall downward trend of rIDPs burden globally, there have been sporadic resurgences in ASMR over the past three decades. For instance, a clear ASMR increase was observed in low SDI regions during 2011–2014 with an APC of 1.58% (95% CI: 0.74, 2.42%). Low-middle SDI regions showed an increasing ASMR trend during 2005–2010 (APC: 2.59%, 95% CI: 2.28, 2.89%). Even high SDI regions also showed a resurgence in ASMR of rIDPs in 2000–2003 (APC: 7.54%, 95% CI: 2.63, 12.69%) and 2010–2017 (APC: 1.85%, 95% CI: 1.22, 2.48%) (Additional file 1: Tables S8–S12).

Associations of age-standardized DALY rates and age-standardized YLD rates of rIDPs (per 100,000 population) with SDI values by countries and territories and GBD super regions in 2021. (A Association between age-standardized DALY rates and SDI values. B Association between age-standardized YLD rates and SDI values.) The top right panels show the classification of GBD super regions. The expected values based on age-standardized rates and SDI values by a smoothing spline model with Locally Weighted Scatterplot Smoothing method are shown in the black lines. DALY disability-adjusted life-year; GBD global burden of disease; rIDP rare infectious disease of poverty; SDI socio-demographic index; YLD year lived with disability

Temporal trends of age-standardized DALY rates and age-standardized YLD rates of rIDPs by SDI levels from 1990 to 2021. DALY disability-adjusted life-year; rIDP rare infectious disease of poverty; SDI socio-demographic index; YLD year lived with disability

Age and sex heterogeneity in disease burden were observed for the age-standardized DALY rates associated with rIDPs, and the populations aged under 15 years and females were nearly predominated. In 2021, the age-standardized DALY rates in females were 227.35 per 100,000 population (95% UI: 162.72, 301.01 per 100,000 population) among people aged < 5 years, 92.43 per 100,000 population (95% UI: 64.19, 133.97 per 100,000 population) among those aged 5–9 years, and 77.90 per 100,000 population (95% UI: 54.01, 111.73 per 100,000 population) among those aged 10–14 years. In comparison, the values were 263.19 per 100,000 population (95% UI: 176.06, 344.74 per 100,000 population), 79.08 per 100,000 population (95% UI: 52.65, 113.90 per 100,000 population), and 40.76 per 100,000 population (95% UI: 28.12, 58.43 per 100,000 population) among the three serial age subgroups in males (Fig. 4). The sex disparity of age-standardized DALY rates was clear in the population aged 15–49 years, with estimates of 48.05 per 100,000 population (95% UI: 33.02, 67.19 per 100,000 population) in females and 11.95 per 100,000 population (95% UI: 8.81, 15.78 per 100,000 population) in males. Similarly, the sex disparity in age-standardized YLD rates was observed in the same age group, with the value of 44.41 per 100,000 population (95% UI: 29.59, 63.54 per 100,000 population) in females and 6.15 per 100,000 population (95% UI: 4.02, 9.56 per 100,000 population) in males. During 1990–2021, males had a larger reduction in ASPR (AAPC: − 0.61%, 95% CI: − 0.65, − 0.57%) and age-standardized DALY rate (AAPC: − 0.26%, 95% CI: − 0.34, − 0.19%), compared with females (AAPC of ASPR: − 0.08%, 95% CI: − 0.10, − 0.06% and AAPC of age-standardized DALY rate: − 0.10%, 95% CI: − 0.14, − 0.07%). The age- and sex-specific patterns for age-standardized prevalence, mortality, and YLL rates of rIDPs are presented in Additional file 1: Fig. S5.

Age-standardized DALY rates and age-standardized YLD rates of rIDPs (per 100,000 population) by age groups, sex, and SDI levels in 2021. (A Age-standardized DALY rates of rIDPs. B Age-standardized YLD rates of rIDPs). In each panel, the horizontal coordinate represents age stratification at a 5-year interval, and the color of the columns represents sex stratification (females in red and males in blue). Error bars represent the corresponding 95% uncertainty intervals. DALY disability-adjusted life-year; rIDP rare infectious disease of poverty; SDI socio-demographic index; YLD year lived with disability

Projection results from the BAPC model suggest that the global burden of rIDPs would continue to decline mildly. By 2050, the projected ASPR of rIDPs would be 1205.17 per 100,000 population (95% CI: 682.39, 1727.95 per 100,000 population), and the age-standardized DALY rate would be 53.21 per 100,000 population (95% CI: 18.30, 88.13 per 100,000 population). Countries and territories with low SDI levels, particularly in Western sub-Saharan Africa, are projected to suffer the highest burden of rIDPs. Meanwhile, the ASPRs in Oceania, South Asia, and Western sub-Saharan Africa are projected to remain high (Additional file 1: Table S15). The projected disease burden by sex showed declined trends in the same direction, while females would still have higher ASPR, age-standardized DALY and YLD rates than males by 2050 (Table 3).