Trend of brucellosis incidence and age-period-cohort model analysis in Shandong Province from 2005 to 2024

To analyse the trend of brucellosis incidence and the changes in incidence rate with the age-period-cohort model in Shandong Province from 2005 to 2024, and provide a theoretical basis for the prevention and control strategy of brucellosis. The incidence rate data of human brucellosis reported by the infectious disease reporting system of China Disease Prevention and Control Information System from 2005 to 2024 in Shandong Province were collected. The annual change percentage (APC) and annual average change percentage (AAPC) of the incidence rate were calculated using the joinpoint software. The Age Period-cohort (APC) model was used to analyze changes in brucellosis incidence with age, period, and birth cohort effects. The average annual reported incidence of brucellosis in Shandong Province from 2005 to 2024 was 1.88 per 100 000. The joinpoint results showed that the reported incidence of brucellosis showed an alternating trend of first decreasing and then increasing, with average annual decreasing and increasing rates of -0.7%(2005–2009), 75.3%(2009–2015), -12.4%(2015–2019) and 6.7%(2019–2024), respectively. The results of APC model showed that the risk of brucellosis increased rapidly with the increase of age group, and the risk coefficient was the highest in the age group over 80 years old. The incidence of brucellosis increased slowly at first, increased rapidly and then decreased (χ2 = 795.63, P = 0.000), and reached a peak in 2017 (RR = 2.779, 95% CI:2.568–3.007), the lowest in 2007 (RR = 0.149, 95% CI:0.123–0.181); The incidence increased with the age of birth (χ2 = 126.74, P = 0. 000). From 2005 to 2024, the reported incidence of brucellosis in Shandong Province showed a significant age-period-cohort effect, which showed an overall trend of first increasing and then decreasing. The incidence risk increased rapidly with the increase of age, slowly increasing first, rapidly increasing then decreasing with the passage of time, and increasing with the passage of birth cohort. Health education should be targeted to reduce the risk of brucellosis.