Overview of global burden of STH infectionsGlobal burden of STH infections

In 2021, there were an estimated 642.72 million cases and 1.38 million DALYs caused by STH infections, among which, 293.80 million cases and 647.53 thousand DALYs caused by ascariasis, 112.82 million cases and 540.20 thousand DALYs caused by hookworm diseases, and 266.87 million cases and 193.92 thousand DALYs caused by trichuriasis. A total of estimated 3472 deaths caused by STH infections, mainly by ascariasis (Supplementary Table 1).

The global age-standardized prevalence rate (ASPR) of STH infections was 8429.89 (95% UI: 7697.23, 9362.18] per 100,000 population, decreased by 69.6% (95% UI: 0,65, 0.73) compared to that in 1990. Specifically, the ASPR of ascariasis was 3856.33 (95% UI: 3133.93, 4760.38) per 100,000, dropped by 75.8% (95% UI: 0.68, 0.81) compared with that in 1990. The global ASR of hookworm disease was 1505.49 (95% UI: 1418.67, 1598.89) per 100,000, fell by 82.9% (95% UI: 0.81, 0.85) compared with that in 1990. The ASPR of trichuriasis was 3482.27 (95% UI: 3147.21, 3898.86) per 100,000, reduced by 59.9% (95% UI: 0.51, 0.67) compared with that in 1990. When calculated by disability-adjusted life years (DALYs), the global ASR of DLAYs caused by STH infections was 18.84 (95% UI: 12.61, 27.31) per 100,000 in 2021, dropped by near 82% (95% UI: 0.80, 0.84) compared with that in 1990. While the global ASR of DLAYs per 100,000 caused by ascariasis, hookworm disease, and trichuriasis was 9.05 (95% UI: 6.16, 12.45), 7.26 (95% UI: 4.52, 11.11), and 2.53 (95% UI: 1.40, 4.13), respectively, with drop rate ranging from 74.7 to 82.7% (Supplementary Table 1).

Distribution

The prevalence of STH infections varied across 21 geographic regions in 2021 which were most prevalent in the majority of African and some regions of Latin American locations. The ASPR in Andean Latin America reached 30,153.70 (95% UI: 26,076.80, 34,143.48) per 100,000, followed by Central sub-Saharan Africa 22,494.62 (95% UI: 19,311.10, 25,719.52), while there were no/seldom cases estimated in Europe and Australasia. Similarly, Oceania with ASR of DALYs of 93.36 (95% UI: 57.09, 143.72) and Central sub-Saharan Africa with 65.50 (95% UI: 43.11, 98.66) per 100,000 suffered more from STH infections that any other regions (Table 1).

Table 1 ASR of prevalence and DALYs of STH infections in 21 geographic regions

STH infections were most prevalent in countries located in middle regions of Africa and Americas, and some Asian countries, with the ASPR ranging from 13,046.00 to 50,502.40 per 100,000 in 2021. While North American and European countries had an extreme low prevalence, even to zero. In some specific countries, for example, the ASPR of STH infections in Somalia was much higher than any other countries, reaching 50,502.38 (95% UI: 42,702.02, 58,117.72) per 100,000, followed by the three countries, Peru (38,256.98, 95% UI: 2085.05, 44,729.36), Nicaragua (31,918.37, 95% UI: 25,863.19, 37,674.37), Chad (30,616.25, 95% UI: 23,853.97, 38,950.70). With regard to ASR of DALYs caused by STH infections, Somalia also ranked the first with 307.46 (95 UI 187.99, 484.48) per 100,000. The ASR of DALYs in following five countries/territories, Rwanda, Chad, Guinea, Papua New Guinea, Central African Republic, ranged from 100 to 156 per 100,000.

Trend in the globe and various SDI level

Globally, The ASPR of STH infections had an obvious decrease trend worldwide [estimate annual percent change (EAPC) = − 4.03, 95% CI: − 4.13, − 3.93], from 27,728.35 (95% UI:  25,660.30, 29,899.61) in 1990 to 8429.89 (95% UI: 7697.23, 9362.18) per 100,000 in 2021. During the same period, the ASPR of ascariasis dropped (EAPC = − 5.07, 95% CI − 5.28, − 4.85) from 15,930.11 (95% UI: 13,515.38, 18,419.92) to 3856.33 (95% UI: 3133.93, 4760.38) per 100,000; the ASPR of hookworm disease dropped (EAPC: − 5.61, 95% CI: − 5.95, − 5.20) from 8805.82 (95% UI: 7809.61, 10,049.50) to 1505.49 (95% UI: 1418.67, 1598.89) per 100,000; while the downward trend of trichuriasis was quite slower compared with the other two species infection (EAPC = − 2.69, 95% CI: − 2.91, − 2.46), from 8690.82 (95% UI: 7466.72, 10,146.42) to 3482.27 (95% UI: 3147.21, 3898.86) per 100,000. The ASR of DALYs caused by STH infections had a more pronounced decline (EAPC = − 5.71, 95% CI: − 5.87, − 5.55) from 103.83 (95% UI: 70.38, 153.46) to 18.84 (95% UI: 12.61, 27.31) per 100,000 during the study years, among which, the ASR of DALYs caused by ascariasis and hookworm disease dropped about sixfold, while trichuriasis dropped about fourfold.

The distribution of disease burden of STH infections was negatively correlated with SDI. In low SDI regions, the ASPR of STH infections was 15,665.55 (95% UI: 14,203.48, 17,110.50) per 100,000 in 2021, with ASR of DALYs reaching 55.06 (95% UI: 37.16, 79.09) per 100,000; while in high SDI locations, the ASPR of STH infections was 15.84 times lower than in low SDI locations [989.36 (95% UI: 774.22, 1213.66) per 100,000], and the DALYs rate was much lower [0.10 (95% UI: 0.05, 0.16) per 100,000].

The downward trend varied across different SDI regions. In high SDI regions, the ASPR of STH infections decreased (EAPC = − 2.39, 95% CI: − 2.94, − 1.85) from 2402.29 (95% UI: 1957.70, 2899.51) in 1990 to 1159.30 (95% UI: 913.03, 1449.96) in 2021 per 100,000, with ASR of DLAYs dropped (EAPC = − 13.16, 95% CI: − 14.71, − 11.57) from 3.52 (95% UI: 5.99, 1.83) to 0.95 (95% UI: 0.52, 1.63) per 100,000. So did the trend pattern in high-middle SDI regions with higher rate of prevalence and DALYs. In middle SDI regions, both the ASR of STH infections prevalence and DALYs decreased from 1990 to 2021, the former dropped (EAPC = − 5.08, 95% CI: − 5.30, − 4.86) from 32,436.91 (95% UI: 29,251.24, 35,967.88) to 7415.66 (6614.87, 8460.69) per 100,000, with later dropped (EAPC = − 8.18, 95% CI: − 8.53, − 7.83) from 92.32 (95% UI: 56.45, 143.08) to 9.09 (95% UI: 5.59, 14.43) per 100,000. Such downward pattern is similar in low-middle SDI regions. In low SDI regions, the ASPR of STH infections (per 100,000) fell (EAPC = − 3.71, 95% CI : − 4.05, − 3.37) from 48,748.62 (95% UI: 46,296.71, 50,880.93) to 15,665.55 (95% UI: 14,203.48, 17,110.50) with ASR of DLAYs falling (EAPC = − 5.21, 95% CI: − 5.52, − 4.89) from 274.59 (95% UI: 196.49, 382.67) to 55.06 (95% UI: 37.16, 79.09) during the study years. When it comes to specific species infection in 2021, the most prevalent was trichuriasis in high, high-middle and middle SDI regions, but ascariasis in low-middle and low SDI regions; While the DLAYs caused by STH infections was approaching zero in high and high middle SDI regions, but remained a serious public health problem in middle and low-middle SDI regions, DALYs caused by hookworm disease and ascariasis in low SDI regions in particular (Fig. 1).

Fig. 1

Trend of ASR of prevalence and DALYs (per 100,000) of STH infections in the globe and different SDI regions. a Trend of ASPR of STH infections in the globe and different SDI regions, b Trend of ASR of DALYs caused by STH infections in the globe and different SDI regions. ASR age-standardized rate, ASPR age-standardized prevalence rate, DALYs disability-adjusted life-years, SDI socio-demographic index, STH soil-transmitted helminth

Age and gender differences in STH infections

There was no significant difference between genders observed in each age group. The ASR of STH infections prevalence and DALYs were various across different age intervals. The rate of prevalence was higher in the groups of 5–19 years, especially the group of 5–9 years with the rate of prevalence of 16,263 (95% UI: 14,877.06, 18,003.49) and DALYs of 40.69 (95% UI: 25.98, 60.91) per 100,000 and reduced with the increase of ages (Fig. 2). As for specific species infection, ascariasis had a similar pattern and was also most prevalent in the group of 5–14 years, with the rate of prevalence 8029.41 (95% UI: 6646.23, 9775.80) and DALYs of 13.57 (95% UI: 8.45, 21.41) per 100,000. Hookworm disease had also a highest rate in the group of 5–9 years, with the prevalence of 3687.23 (95% UI: 3462.76, 3917.55) and DALYs of 20.30 (95% UI: 12.86, 31.24) per 100,000. Trichuriasis was mainly prevalent in the group of 5–29 years, the group of 5–9 years in particular with the rate of prevalence of 5578.97 (95% UI: 5092.24, 6159.89) and DALYs of 20.30 (95% UI: 12.86, 31.24) per 100,000 (age and gender difference for specific species infections, Supplementary Figure 1).

Fig. 2

Age and gender difference in STH infections. a Rate of STH infections prevalence, b Rate of DLAYs by STH infections. DALYs disability-adjusted life-years, STH soil-transmitted helminth

Association between STH infections and SDI in 21 geographical regions

At regional level, the ASRs of STH infections prevalence (r = − 0.8807, P < 0.0001) and DALYs (r = − 0.9069, P < 0.0001) were negatively correlated with SDI among regions. Southern sub-Saharan Africa, Latin America and Caribbean had higher-than-expected ASPR, while central Asia and central Europe had a lower-than-expected ASPR based on their SDI between 1990 and 2021 (Fig. 3).

Fig. 3

ASR of prevalence (a) and DALYs (b) of STH infections in 21 GBD regions by SDI, 1990–2019. Expected values, based on SDI and disease rates in all locations, are shown as a solid line; expected values based on a calculation accounting for the SDI and disease rates across all locations. 30 points are plotted for each region and show the observed age-standardized rate of prevalence or DALYs for each year from 1990 to 2021 for that region. The shaded area indicates the 95% confidence interval of the expected values. Points above the solid line represent a higher-than-expected burden, and those below the line show a lower-than expected burden. ASR age-standardized rate, DALYs disability-adjusted life-years, GBD Global Burden of Diseases, SDI socio-demographic index, STH soil-transmitted helminth

The ASRs of ascariasis prevalence (r = − 0.8561, P < 0.0001) and DALYs (r = − 0.9064, P < 0.0001) were negatively correlated with SDI among regions. The ASR of ascariasis was scattered higher and lower of the expected value between 1990 and 2021. Oceania had a lower-than-expected ASPR based on their SDI.

The ASRs of hookworm disease prevalence (r = − 0.8826, P < 0.0001) and DALYs (r = − 0.8840, P < 0.0001) were negatively correlated with SDI among regions. Southern sub-Saharan Africa had higher-than-expected ASPR, while western sub-Saharan Africa, South Asia, and North African and Middle East had a lower-than-expected ASPR based on their SDI between 1990 and 2021.

The ASRs of trichuriasis prevalence (r = − 0.7164, P < 0.0001) and DALYs (r = − 0.7841, P < 0.0001) were also negatively correlated with SDI among regions. Central Latin America had higher-than-expected ASPR, while North African and Middle East and Central Asia had a lower-than-expected ASPR based on their SDI between 1990 and 2021 (Supplementary Figure 2).