Human immunodeficiency virus (HIV) disease is one of the most common diseases in the world. In 2022, 33.1 to 45.7 million people were living with this disease and 29.8 million people had access to antiretroviral therapy [1] . The Central and West Africa region was home to more than 12% of these patients [2] . In 2022, Chad had more than 82.000 people who were on antiretroviral treatment (ART) [3] and many of whom do not have access to viral load [4] [5] despite the relentless efforts of the government and its partners [6] . While viral load is used to measure the effectiveness of ART [7] , it is also an indicator to assess the third UNAIDS HIV performance indicator [8] . Monitoring viral load minimizes Treatment failures by adapting treatment according to the levels of treatment failure observed, which according to studies varies between 14 and 53% after 6 to 24 months of treatment initiation [9] . This makes it possible to reduce new infections as much as possible [10] or even the eradication of the disease [11] [12] , because the suppression of the viral load is synonymous with non-transmission [13] . However, treatment failure is defined as any viral load greater than 1000 copies/mL after at least 6 months of antiretroviral therapy [14] . It is also the lack of control of the virus that may be due to poor compliance or resistance of HIV to one or more antiretroviral molecules [15] . It should be noted that virological failure is a double punishment for patients. Antiretroviral drugs (ARVs), which are effective drugs against HIV, can also be harmful to the kidneys and liver [16] which over time, leads patients to problems of immune deficiency, metabolic diseases (kidney failure, metabolic hepatitis, etc.), among other things.

In Chad, given the absence of the genotyping test for the diagnosis of HIV resistance, clinicians rely mainly on virological failure criteria to better manage patients therapeutically according to the national protocol.

The objective of this study was to assess the level of treatment failure in person living with HIV on antiretroviral treatment who had achieved a viral load at the National Reference Laboratory for HIV and Hepatitis (LNR-HIV-Hep) in N’Djamena.

A total of 4890 patients were included in the study, of which 3443 (70.4%) were women and 1447 (29.6%) were men, for a female/male ratio of 2.4. The mean age was 38 years with extremes of (20 - 75) years.

Among of 4890 patients who achieved the viral load, 881 (18.0%) were in treatment failure (≥log3 or ≥1000 copies) according to the 2018 WHO guideline.

Table 2 describes the distribution of patients by viral load suppression, sex, and marital status.

The majority of patients were married (60.9%), followed by single (16.6%), divorced (13.9%) and widowed (8.6%). In terms of virological failure, 59.6% of patients with an unsuppressed viral load are married, 22% are single, 12.1% are divorced and 6.2% are widowed.

Distribution of patients according to treatment regimen, viral load suppression and gender

Table 3 describes the distribution of patients according to treatment regimen, viral load suppression and gender.

In terms of failure by regimen, 50.3% (444/881) were on TDF/FTC/EFV, 37.7% (333/881) were on TDF/3TC/DTG, 3.9% (35/881) on TDF/FTC/ATZ, 2.9% (26/881) were on AZT/3TC/EFV-based regimen, 1.9% (17/881) were on ABC/3TC/LPV-based regimen, 1.5% (14/881) were on TDF/FTC-based regimen, and 1.3% (12/881) were on ABC/3TC/ATV-based regimen.

Distribution of patients according to viral load suppression, gender and duration of treatment

Table 4 describes the distribution of patients by viral load suppression, gender, and duration of treatment.

The majority of patients had been on treatment for between five (05) and ten (10) years, respectively 52.7% (2578/4890) and 32.8% (1603/4890). 13.9% (680/4890) had been on treatment for fifteen (15) years and 0.6% (28/4889) had been on treatment for more than twenty (20) years.

In patients with virological failure, 0.5% (4/881) of patients with treatment failure had been on treatment for more than 20 years, 11.9% (105/881) had been on treatment for more than 15 years, 54.9% (484/881) had been on treatment for less than 10 years 32.7% (288/881) had been on treatment for less than 5 years.

It should be noted that all these patients should be switched to the dolutegravir-based regimen.

Allocation of patients according to viral load suppression, gender and adherence

Table 5 describes the distribution of patients according to viral load suppression, sex and adherence.

The non-compliance rate was 3.7% (179/4890) in all patients. It was 4.3% (38/881) in patients with treatment failure. 18.2% (892/4890) of all patients do not know whether they are compliant or not. Among those who failed treatment, 15.8% (139/881) did not know whether they were compliant or not.

The ratio of 2.4 shows that the number of women people living with HIV on ART in Chad was higher than men. This remark was also reported in the 2022 statistical yearbook of the Ministry of Health and Prevention. The average age was 38 years, which means that the Chadian population is very young and the disease mainly affects age groups that are very sexually active. This could explain the high percentage found among married patients (60.9%), followed by bachelors (16.6%). The low percentage found among divorced women (13.9%), followed by widowers (8.6%), and clearly confirms that HIV circulates in the sexually active young population. It is important to implement HIV eradication strategies adapted to the Chadian context within this population.

The treatment failure rate in person living with HIV in this study is 18.0% (881/4890). Similar results were reported by Endalamaw et al. 2020 [18] , Wadonda et al. 2012 [9] , and Lailulo et al. (2020) [4] . This could explain the high percentage found among married patients (60.9%), followed by bachelors (16.6%). The low percentage found among divorced women (13.9%), followed by widowers (8.6%) and clearly confirms that HIV circulates in the sexually active young population. It is important to implement HIV eradication strategies adapted to the Chadian context within this population. Inadequate overall management and neglect of the patients themselves could explain this high percentage. It should be noted that comprehensive management of HIV is based on an approach that combines blocking the development of the virus, strengthening the immune system and regular monitoring of viremia (viral load). This approach is difficult and costly for countries with limited resources and fewer qualified personnel. This is sometimes compounded by insufficient availability of drugs and reagents for immunological and virological (viral load) monitoring.

The main factors of treatment failure reported in the studies are age, adherence, anemia, treatment interruptions, education level, low CD4 count, treatment interruptions and virus resistance [19] - [22] .

The 59.6% virological failure in married patients is worrying, as it increases the risk of HIV transmission in married women when they become pregnant and has been very well monitored.

It should be noted that the treatment failure observed in patients on second-line treatment and in patients who observe could be due to a phenomenon of resistance of HIV-1 to treatment, which has also been reported in several studies [23] [24] . A recent study reported by Keita et al. 2020, established the existence of HIV1 virus resistance genes against non-nucleotide reverse transcriptase inhibitors (NNRTIs) and reverse transcriptase nucleotides (NRTIs) in Chad [25] .

However, the treatment failure observed in non-compliant patients could be explained by patient negligence or poor therapeutic education. This observation has also been reported by other studies [26] . Patients who do not know whether they are compliant or not may be classified as careless or in poor therapeutic education. With a non-compliance rate of less than 5%, Chad could achieve the 95% target of eliminating the patient burden if patient support and retention strategies are strengthened. It is therefore necessary to develop therapeutic education strategies for these patients and to provide psychological support.

Virological failure in patients on ART based on DTG 37.7% (333/881) for more than a year of treatment needs to be investigated and shed more light on the reasons, because in recent years, studies have reported resistance of the virus to integrase inhibitor molecules [27] [28] .

The rate of treatment failure observed in persons living with HIV on ART for more than 10 years is very worrying [6] , as these patients should be switched to the dolutegravir-based regimen. While virological failure is observed in patients on this regimen. Virological failure in person living with HIV on ART for more than 10 years is a catastrophe from a physiological point of view [29] , because liver or kidney poisoning is a real disorder for the body. This most often leads patients to other metabolic diseases with disastrous consequences.

The study showed that many of the patients have been on treatment for several years, but the treatment does not respond. The study of the resistance of the HIV1 virus to the molecules used in Chad and the implementation of resistance tests are necessary. It is also necessary to develop therapeutic education strategies and provide psychological support for non-compliant patients and patients who do not even know whether they are compliant or not.

Study conception and design: Hassan Mahamat Ali (HMA) and Seid Idriss Ahmat (SIA). Data collection and analysis: HMA. Coordination of the survey and correction of the manuscript: Chatté Adawaye, Tapsoba François and Savadogo Aly. All authors have corrected the final version.

The study was unable to determine the number of previous viral loads achieved by each patient in treatment failure, in order to understand whether the patient had already experienced a previous treatment failure. It was also unable to identify the factors contributing to virological failure.