Sunday, June 16, 2024

Regional differences of Mycobacterium tuberculosis complex infection and multidrug resistance epidemic in Luoyang – BMC Infectious Diseases

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The continued decline in TB cases is testament to the remarkable success of the global anti-TB program, but the gap between new and reported TB cases was estimated to be about 3 million in 2019, whis is a warning that the continued decline in reported TB may be partly due to under-reporting and under-diagnosis [15]. The COVID-19 pandemic was bound to exacerbate such shortcomings and directly affected the outcome of TB diagnosis and treatment [16], which is not conducive to accurate assessment of the current epidemic situation of TB and its prevention and control. Therefore, we investigated the epidemiology of TB in the local area during the COVID-19 pandemic, to gain an overall view of the prevalence of TB and multidrug resistance, and provide support for the overall planning of local anti-TB measures.

During the study period, the local rates for MTBC and MDR-TB showed a downward trend, which is beneficial for local TB control strategies and improvement of treatment capacity; however, the impact of COVID-19 prevention and control measures cannot be ignored [17]. From 2020 to 2022, the number of confirmed, suspected and unexcluded TB cases in designated hospitals was 121/100,000 in the main urban area and 338/100,000 in the county and township areas, and the ratio of the number of MTBC-positive cases in the county and township areas to the main urban area was 1.7. In China, about 71% of TB patients live in rural areas [18], and the large population base, shortage of public health resources, and poor medical facilities are disadvantages to the implementation of TB prevention and control [19]. In recent years, China’s economic reforms and urbanization have lifted many non-urban residents out of poverty and some have become a new type of urban dweller, but their benefits in urban health insurance are limited due to the household registration system (hukou system) [20]. In addition, due to the limitations of education and other factors, their work is mainly manual labor, and these socioeconomic barriers can also lead to a higher risk of TB compared with urban residents [21].

The detection rate of MTBC in the main urban area was significantly higher than in the county and township areas (32.8% vs. 10.9%) in patients attending designated TB hospitals. Due to the gap in medical level, the control of screening criteria for TB patients in county and township areas is not strict, and the quality of sputum samples is low. This was demonstrated by the smear-positive rate in different regions, which was 27.0% in the main urban area and only 9.2% in the county and township areas. The latter areas even lack the necessary infrastructure for TB screening, which may lead to some cases not being reported due to insufficient diagnosis and treatment. In addition, the main urban area has a robust TB reporting system, more abundant diagnostic resources, and more convenient medical institutions, making TB diagnosis and reporting more rapid and timely.

The spread of MTBC is a complex process, and factors such as household registration policy, age, sex and nutritional status can lead to differences in characteristics of TB patients [22]. Local TB epidemics and people with a high burden of MDR-TB are concentrated in male and re-treated patients and those younger than 61 years. Therefore, MTBC screening in TB-designated hospitals should be considered in these groups in order to control the spread of TB more effectively.

The overall positive rate of MTBC was 14.5% and 13.5% in the newly diagnosed group, which is higher than the 55/100,000 people announced by the WHO in 2021 [1], indicating that the prevention and control of TB has a long way to go. The incidence of TB is significantly higher in males than in females, and in 2018, WHO reported that the global TB burden was 56% in adult males and 32% in adult females [23]. The male to female ratio of TB cases in our study was 2.7, which may be related to a wider range of activities, more physical exertion, and poor lifestyle habits among males [24]. The prevalence of MTBC in designated TB hospitals in the main urban area was mainly concentrated in the group aged > 60. In this age group, the urbanization process is accelerated, the aging population is serious, and more susceptible to TB because of factors such as low immunity and malnutrition [25, 26]. The opposite is true for county and township areas, where the higher prevalence of MTBC was in individuals aged 

The positive rate of MMCA detection was 81.0% in the smear-positive and 5.3% in the smear-negative patients. Molecular diagnosis is considered to be more time-efficient and has higher sensitivity and specificity than traditional methodology [27]. The recent widespread application of molecular detection techniques has sometimes resulted in their diagnostic role being over-emphasized, while ignoring their limitations, such as being susceptible to antimicrobial drugs and prone to false-positive results. Also, the commercial kit used in this study is not able to detect nontuberculous mycobacteria. This means that attention should be paid to combination of traditional and new methods for diagnosis and treatment of TB. In the smear-positive patients, the positive rate of MTBC was higher in the main urban area than in the county and township areas (91.7% vs. 74.9%), but in the smear-negative patients, it was lower in the county and township areas than in the main urban area (4.4% vs. 11.0%). This indicates that the medical institutions in the county and township areas had excellent performance for exclusion of TB, but there was a difference in the confirmed diagnosis of TB compared with the main urban area, so it is necessary to pay attention to the false positives of tuberculosis diagnosis for confirmed cases reported by smear-positive as a detection method in county and township areas.

The detection rate of MDR-TB in the main urban area was significantly higher than that in the county and township areas. Due to the particularity of medical policies (The registered permanent residence system in China has little impact on the treatment of confirmed cases), confirmed cases of TB in different residences, especially some complex, refractory and unsuccessful treatment cases were concentrated in the main urban area with relatively abundant medical resources, which is a major reason for the high MDR detection rate in the main urban areas [28]. In addition, high mental stress, poor medication compliance, irregular treatment, drug abuse, and direct spread of MDR strains [29,30,31] are all reasons for the high drug resistance of MTBC in the main urban area.

In 2019, there were 361,920 MDR-TB cases worldwide, and these may have arisen through secondary acquisition of resistance [32]. In our study, the MDR-TB rate in the local re-treated population was 45.2%, while it was as high as 79.3% in the main urban area. A history of TB treatment and irregular treatment resulted in higher detection of MDR-TB in this group compared with the newly diagnosed group [33].

The prevalence and drug resistance of TB vary regionally, with female and young groups at high risk of MDR-TB in some areas, while older and male groups are strongly associated with MDR-TB in other regions [15]. The detection of TB in the main urban area was concentrated in the 41–60 years age group, compared with 25–40 years in the county and township areas. Overall, individuals with a history of TB treatment, male sex, and age 

Our study had several limitations. First, study participation was voluntary, which may have led to missed detection of some hidden cases of TB or the failure of some patients to be fully monitored due to economic and other reasons. There were insufficient data for some particular groups of TB patients, such as older patients in remote areas, patients with poor economic conditions, and patients who have less understanding of TB and reluctance to visit the doctor. These factors could have led to bias in the study of TB in our area. Second, some sputum specimens were of low quality, which could have affected the final MTBC detection rate, and led to some false-negative results and a lower TB infection rate than is actually present.

Despite the shortcomings, we covered a wide area of Luoyang City, and we believe that our results do reflect the epidemiology of MTBC and its drug resistance characteristics in local urban and county and township areas. Our findings may be applicable to TB epidemics across the whole of China during the particular period of the COVID-19 pandemic but not in areas with high TB incidence, large-scale outbreaks, and poorly controlled TB.

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