Tuberculosis and HIV co-infection remains one of the most public health challenges in Southwest of China. In the study, we found an overall TB treatment success rate of 89.5% for 3183 TB patients living with HIV in five years (2016-2020), which is higher than the national treatment successful rate of 76.0% in 2018, and is nearly in agreement with studies conducted in Asian countries like in Vietnam 74.0% ; in Indian 80.0% ; in Thailand 74.3% . However, this rate affects the target of achieving the 90% TB treatment success rate for TB patients set by Global Plan to stop TB 2011-2015 .
Based on their self-descriptions, the majority of the TB patients living with HIV were males which is in line with findings from other literature . Majority, at 42.3% and 39.3% of MTB/HIV patients were in the age groups of 21-40 and 41-60 years respectively. This report is also in agreement with studies by Mekonnen D et al . Most of the patients were of Han ethnicity and farmers. This study also revealed high proportions of MTB/HIV among new cases, diagnosed with PTB, sputum smear-negative TB, HIV antibody positive and received ART.
Univariate regression analysis showed that male, aged above 60 years old, of Han ethnicity, sought medical aid at the city-level of medical institute, EPTB, relapse or return treatment after default and positive initial sputum smear result were the risk factors for unsuccessful treatment outcome. However, the odds of gender and ethnicity were not statistically significantly different among MTB/HIV patients compared to the reference group in the multivariable regression model.
This study showed that patients aged exceed 60 years old had higher odds of developing poorer outcomes compared to other age groups. The effect of age on treatment outcome may be more sophisticated to explain. As a matter of fact, many studies have had a similar result that advanced age is associated with unsuccessful outcome in TB treatment . Not surprisingly, advanced age is a risk factor for mortality among TB patients with or without HIV. In part this finding could be contributed to age-related decreases in immunity , making a person more susceptible to infection, as growing older may lead to poor outcomes . In addition, this findings are based on secondary data from routine surveillance, so we could not control for the age-related confounding variables.
In this study, the medical institute where a MTB/HIV patient sought medical aid was found to be linked with unsuccessful outcome. The odds of having unsuccessful TB treatment outcome was 2.136 times higher among patients seeking medical aid at the city-level medical institutes than that at the county-level institutes. This is similar to earlier reports from a study conducted in Zambia  and a study done in northern Ethiopia . MTB/HIV co-infection patients who visit county-level medical institutions mostly seek medical advice after they have high-risk behaviors that may be infected with HIV, so that they can know their HIV infection status timely and be diagnosed early. Then they can receive antiviral and anti-tuberculosis treatment nearby. On the contrary, the patients who choose to seek treatment in municipal medical institutions might because their immune system has been severely damaged, and opportunistic infections or AIDS-related diseases are discovered when they seek medical treatment, which is late and severe, thus affecting the treatment effect of patients with dual infection. This is an area that needs to be studied in the future to see what risk factors exist in different locations that may put people at higher risk of unfavourable outcomes in the TB treatment.
The MTB/HIV patients on the relapsed or returned treatment after default category had a higher chance of unsuccessful treatment outcome than the new cases. This result was similar to that reported from Brazil . Mycobacterial resistance, a direct consequence of having been exposed to lack of treatment adherence or lost to follow up that contributes a lot to these unfavourable treatment outcomes. Hence, it should be aware of that adherence to treatment is one of the most important topics in the public policy agenda in view of the difficulty to manage the double burden of disease . Nevertheless, a study conducted in Nigeria did not find any association between new and relapse patients .
Regarding the site of TB infection in the NTSS, cases registered as EPTB were 111.5% more likely to develop unsuccessful outcome than PTB (p<0.05). Higher levels of immunosuppression increase the likelihood of EPTB or simultaneous EPTB and PTB, all of that are hard to cure . Another study showed that EPTB is more common in the HIV-associated TB population, it becomes increasingly prevalent with progressive immunodeficiency, and it contributes to unfavorable treatment outcomes .
Finally, our study found that the chance of unsuccessful outcome was higher among MTB/HIV co-infected patients with sputum smear positive compared with the smear negative. Similar findings were reported by other studies conducted in South India  and Eastern Ethiopia . In contrast, a study conducted in Mizan Tepi  demonstrated MTB/HIV co-infected patients with Smear positive PTB had a higher chance of successful TB treatment outcome.
A big strength of the study is that the large sample size allowed us to identify independent risk factors for unsuccessful treatment outcomes. In addition, the study was carried out under routine conditions, meaning the data were representative of the real situation, thus, the findings are generalizable to most of the populous province in China that accounts for a large proportion of PTB patients with HIV co-infected in the country.
Apart from such important findings, this study is not without limitation. One limitation is that the study included only patients who had an initial smear result of either positive or negative. And as common for secondary data based studies, important variables like CD4 level, distance to the health facility, level of education, BMI and economic status that could improve the model predictions were incomplete from the records. Another one is that we should acknowledge that there was a large amount of missing data regarding TB treatment outcome. These missing data could have biased our risk estimates. Bias is always a concern with secondary data sources, but the database of the NTSS has already served as a reliable source for several other population-based studies in China.