# Incidence trend analysis of human brucellosis in the context of human development: an ecological study using joinpoint regression in Iran

## TL;DR

This study finds a slight increase in human brucellosis in Iran over 23 years, with higher human development linked to lower incidence, though other factors may influence this trend.

## Contribution

The study uses joinpoint regression to analyze brucellosis trends in Iran and links them to human development for the first time.

## Key findings

- HB incidence increased slightly but significantly by 0.45% annually from 2000 to 2023.
- A moderate negative correlation was found between HB incidence and the Human Development Index (Spearman’s ρ = −0.54).
- Linear regression showed an inverse association between log(HDI) and HB incidence (β = −65.96, p = 0.044).

## Abstract

Human brucellosis (HB) remains a significant public health concern in Iran, where its burden may be shaped by socio-developmental factors. This ecological time trend analysis explores long-term patterns in HB incidence in the context of human development.

We conducted Joinpoint regression analysis to assess temporal trends in HB incidence from 2000 to 2023 in Iran. The Human Development Index (HDI) was included as a predictor to examine associations using Spearman correlation and linear regression on log-transformed HDI. Residual diagnostics and robust regression techniques were applied.

The overall annual percentage change (AAPC) in HB incidence showed a slight but statistically significant upward trend (+ 0.45%; p = 0.023). Joinpoint regression identified four statistically significant changes in trend. A moderate negative correlation was observed between HB incidence and HDI (Spearman’s ρ = − 0.54). Linear regression indicated an inverse association between log(HDI) and HB incidence (β = − 65.96, p = 0.044), though the explained variance was limited (R² = 0.226).

The findings suggest that higher levels of human development may be associated with reduced HB incidence at the national level. However, this association is likely influenced by unmeasured factors such as access to veterinary care, cultural practices, and surveillance quality. Caution is warranted in interpreting these findings due to the ecological study design and potential underreporting.

The online version contains supplementary material available at 10.1186/s12889-025-25304-5.