This study revealed a statistically significant decline in TB mortality among the elderly in China from 2004 to 2021. This finding was consistent with other studies in China[13] and the global trend[1, 19]. Economic prosperity, leading to improved socioeconomic conditions and living standards (such as better housing and nutrition), contributes to the continued decline in mortality[20]. It may be benefiting from a series of interventions and policies that have been put in place by the government. For instance, China actively promoted the process of controlling the disease, with the full coverage of DOTS strategy being reached around 2004[21]. TB mortality declined at a slower rate in recent years, and the trend was also found in TB incidence[18]. TB mortality varied between gender and age groups, residences and regions. The study revealed that TB mortality was higher among males, in rural areas, and in the western region. These findings were consistent with previous studies[13, 22–25]. The higher TB mortality among males may be attributed to factors such as increased participation in social activities[26], high labor intensity[26], excessive smoking[27] and alcohol consumption[28], poor resistance[29], and incomplete antituberculosis treatment[26]. The higher mortality in rural areas and the western region could be due to lower levels of economic development and accessibility of healthcare services[30]. Patients with higher socioeconomic status are more likely to receive superior treatment and additional diagnostic procedures[31]. We also found different decline rates of TB mortality after stratification by gender, residences and regions.
Due to the intricate interactions among age, period, and cohort factors, we applied the age-period-cohort model and IE algorithm to quantify their net effects on TB mortality. The age effect on TB mortality increased with advancing age. The higher TB mortality among older people may be due to waning immunity and increased comorbidities[32]. Additionally, the older people usually experience a worse prognosis and are often under-treated[33]. Our study showed that compared with female group, aging may have a greater impact on increasing the RR of TB mortality in males. A similar finding for TB incidence was published by Li[34]. Furthermore, this study showed that aging increased the RR of TB mortality in urban areas more than in rural areas, and in eastern regions more than in central and western regions. This was in contrast to the order of TB mortality among the different groups, but the results were not in conflict. This phenomenon can be attributed to TB deaths in rural areas and western regions occurring in relatively younger age groups. Poor economic and educational levels, limited nutrition and insufficient health knowledge affect the survival time of TB patients[35].
The period effect can be influenced by a set of environmental, historical, and economic factors. According to the age-period-cohort analysis, TB mortality decreased with period, consistent with the results of the joinpoint regression model and previous results[25, 36]. Intriguingly, the rate of decline was more pronounced in rural areas than in urban areas. This can be attributed to fast-paced economic growth, enhanced healthcare coverage (especially in rural areas), and rigorous respiratory TB control policies[13]. This finding was contrary to the urban-rural difference in TB incidence. Some studies found that the incidence of TB decreased more significantly in urban than in rural areas in recent years[18, 37]. Moreover, the downward trend after 2012–2016 was not as pronounced as it was before 2012–2016, which reminded us that more attention should be paid to innovative research.
The cohort effect reflected influencing factors that arise earlier in life course and accumulate with life course. The cohort effect on TB mortality showed continuously decreasing trends from the 1927–1931 birth cohort to the 1957–1961 birth cohort, with the exception of certain demographic groups that exhibited a tendency to elevate at the last one or two birth cohorts. The increase in TB mortality among individuals from the 1952–1956 birth cohort and the 1957–1961 birth cohort possibly was related to their early-life exposure to malnutrition. Malnutrition had been demonstrated to be a significant risk factor for TB[38, 39], and a study found that prenatal and early-life exposure to malnutrition may increase the risk of TB in the exposed generation and their offspring[40].
The strength of our study is the nationwide nature of the data and further analysis by gender, urban and rural, and regional categories. The difference between this study and previous national study[13] was that we used data on TB mortality from the National Disease Surveillance Points (DSPs) system instead of the National Notifiable Disease Reporting System (NNDRS) [41]. TB mortality from the NNDRS reflects patients who received treatment instead of all patients, and is defined as death during treatment from any cause. TB mortality in the DSPs is determined by the physician as the cause of death is from TB. However, this study also has several limitations. First, under-reporting of TB deaths should be noted. The data in the DSPs were collected from routine surveillance records. The number of deaths from TB in China may be higher than reported. However, the DSPs system is the only national mortality surveillance system that covers all causes of death in China. And the system has expanded its surveillance population from 6–24% of the Chinese population since 2013, covering almost a quarter of the population. It is the only feasible option for obtaining reliable and valid information on TB mortality in the country. Second, with the increase in monitoring centers from 161 to 605 in 2013, there might be some inconsistency in data collection. Although we used the average of the latter four years in place of the data for 2012 when calculating TB mortality for the period 2012–2016, the findings of this study should still be treated with caution. Third, in addition to gender, urban and rural areas, and regions (eastern, central, and western), factors such as economic levels and comorbidities (such as HIV and diabetes) were not included in the analysis. These factors would also influence the epidemic state and control of TB, and should be considered in future studies.