Since the advent of triple antiretroviral therapy in 1996, HIV infection has entered a new era of hope. Although no cure currently exists, antiretroviral triple therapy and prophylaxis for common opportunistic infections have helped reduce HIV-related morbidity and mortality, improve the quality of life and life expectancy of people living with HIV, and prevent HIV transmission [1]. AIDS-related deaths are estimated to have decreased by 54% since 2010, and 77% of all people living with HIV (PLHIV) are projected to have access to antiretroviral therapy (ART) by the end of 2024 [2].

To significantly reduce the viral load in the blood, initial antiretroviral therapy should ideally combine drugs that act against HIV through at least two different mechanisms of action [1]. A first-line triple therapy is a combination of two nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) with a third agent [3], which can be either a non-nucleoside reverse transcriptase inhibitor (NNRTI) or an integrase inhibitor (II). First-generation NNRTIs, namely efavirenz (EFV) and nevirapine (NVP), were the recommended first-line regimens, in combination with NRTIs such as lamivudine (3TC) and tenofovir (TDF) [4]. However, the prevalence of pre-treatment HIV resistance to efavirenz and nevirapine is gradually increasing among people starting ART. People with pre-treatment HIV drug resistance are less likely to achieve viral load suppression and have a higher probability of virologic failure, treatment discontinuation, and the acquisition of new resistance mutations if treated with NNRTI, so the use of NNRTI-sparing regimens has become a priority [5]. The WHO recommends dolutegravir (DTG)-based therapy as the preferred first-line treatment for adults living with HIV starting ART, and as the preferred second-line treatment for adults living with HIV who have failed non-DTG-based regimens, in low- and middle-income countries due to its high genetic barriers to resistance, fewer drug interactions, reduced side effects, higher viral load (VL) suppression rates, and cost-effectiveness compared to efavirenz [6][7].

The Multiple Indicator Cluster Survey (MICS) conducted in 2014-2015 showed that Chad is experiencing a generalized epidemic with an estimated prevalence of 1.6% in 2015 among people aged 15 - 49, and according to the Spectrum model, it is estimated at 1.1% [0.8 - 1.3] in the same age group [8]. In 2007, Chad made HIV care free of charge. This coverage includes antiretroviral drugs, essential biomedical tests, and medical follow-up.

In Chad, dolutegravir-based ART was adopted as a first-line treatment in 2019. The fixed-dose combination of tenofovir (TDF), lamivudine (3TC), and dolutegravir (DTG) (TLD) was gradually introduced in 2020 for new patients and, at the same time, gradually replaced older regimens [9]. Studies have demonstrated the superiority of DTG-based regimens over efavirenz-based regimens in suppressing viral replication, both as first-line ART [10]-[12] and as second-line ART [13]. DTG has demonstrated excellent efficacy and optimal tolerability as a first-line treatment. Furthermore, switching to a DTG-based regimen from any other antiretroviral treatment has demonstrated non-inferior efficacy [14][15]. The objective of the study is to contribute to the understanding of HIV viral suppression in patients treated with the DTG-based regimen and various other ARV treatment regimens and to identify associated factors.

The study shows that 36.8% of the expected target population underwent viral load testing. This result indicates low engagement among people living with HIV (PLHIV) in ART monitoring and could be attributed to insufficient communication between care sites and PLHIV and/or low enthusiasm among PLHIV for ART monitoring. Viral load testing is considered the preferred method for monitoring the effectiveness of ART, enabling early diagnosis of potential treatment failure and providing information on the development of resistance [18]. The study included 45.8% of PLHIV who underwent viral load testing during the study period. This result could be attributed to incomplete data provided by the investigators, which may have resulted from errors during data collection or entry, leading to the exclusion of incomplete cases and thereby reducing the sample size. Females were the dominant group (98.4%) compared to males (1.6%) in this study. Our finding can be explained, first and foremost, by the fact that the “gender” variable—which contained miscoded data, including missing values—was removed, thereby affecting the representation of males in the sample. Second, our result may be explained by the fact that women are more likely to seek care at health facilities when ill compared to men. Our result is comparable to that of Zhong et al. [19], where 89.1% of the study population was female. The 31 - 45 age group (51.9%) was the most represented. Similar results have been observed in other African studies [12][20][21]. This finding could be explained by the fact that young adults in this age group are sexually active and are at higher risk of HIV infection if preventive methods are not used properly; they are also more likely to undergo HIV testing during routine medical visits, thereby increasing their participation in the care protocol compared to younger and older populations. The most commonly prescribed treatment regimens were TDF + FTC + EFV (60%), followed by TDF + 3TC + DTG (27.8%). Our findings are comparable to those of the study by WHO (2014) [18], in which 33.3% of patients were on a DTG regimen and 66.7% on an EFV regimen. Our results differ from those of Ayal and Behra [22] and Dorward et al. [23], where, respectively, 77.1% and 68.9% were on a DTG regimen and 32.8% and 31.1% were on an EFV regimen. This finding may be explained by the fact that the TDF + FTC + EFV combination was a first-line ARV regimen prescribed as first-line treatment for HIV ART in Chad and was still widely prescribed at the start of the transition to TLD.

Overall, 83.3% of patients had viral suppression (viral load < 1000 copies/mL). Our result is higher than those reported by Asbagui [24]et al. and Fatoumata et al. [25], who achieved viral suppression rates of 54.60% and 73.8%, respectively, but lower than those reported by Analu et al. [26], in which 89.1% of patients achieved viral suppression. Moloko et al. [7] reported a viral load undetectability rate of 87.7%. When patients adhere to their treatment, antiretrovirals prevent HIV from replicating by disrupting the various phases of its replication cycle, resulting in viral load suppression.

The highest rates of viral suppression were achieved with the combinations TDF + FTC + EFV (85.1%) and TDF + 3TC + DTG (85.1%). The viral suppression rate observed with TDF + FTC + EFV (85.1%) is higher than the rates observed with AZT + 3TC + NVP and ABC + 3TC + ATV/R (75% each), ABC + 3TC + LPV/R (60%), and TDF + FTC + ATV/R (66.7%). Our results are comparable to those of the NAMSAL study [27], Ayal and Behra [22], Dorward et al. [23], and Zhong et al. [19], who found viral suppression rates of 74.5%, 69%, 83%, and 100% with the DTG regimen and 69.0%, 66%, 81.4%, and 97.3% with the EFV regimen without DTG. As shown in several other studies, our results demonstrated that regimens containing DTG and EFV lead to better viral suppression compared to other ARV regimens. This finding indicates that DTG was a viable alternative to EFV as a first-line ART.

Viral suppression was similar among patients who had been on treatment for less than one year (85.7%) and those who had been on treatment for 1 to 5 years (84.9%). Devendra et al. [28] reported a rate of 82.9% among children who had been on treatment for less than one year. This result is explained by the fact that at the start of ART, the viral load drops dramatically, demonstrating the potency and efficacy of ARVs in treatment-adherent patients. Non-adherence and potential HIV resistance to ARVs are thought to be responsible for the increase in viral load observed in PLHIV with a long duration of treatment.

By gender, women showed a slightly higher viral suppression rate (83.4%). Our result is comparable to that of Dorward et al. [23], who also observed significant viral suppression (84%) in women. However, our result is higher than those of Semengue et al. [12], Mmatsoku et al. [7], and Coulibaly et al. [29], who obtained results slightly lower than ours in women, but differs from that of Analu´ et al., where high viral suppression was observed in men (66.4%). Several hypotheses may explain the high viral load suppression in women: Women may have better access to ART than men; according to UNAIDS, women are more likely to adhere to HIV treatment than men; from a virological perspective, some studies highlight that women have a lower viral load in the early stages of infection, unlike men [30].

Our results show that viral suppression increased with age, reaching 92.3% among those over 60. Our results are higher than those of Dorward et al. [23], who observed a viral suppression rate of 84.2% among those over 55, but lower than those of Ayal and Behra [22], who found 100% viral suppression among PLHIV over 45. Our result can be explained by the fact that older adults have a better understanding of the disease, leading to good treatment adherence compared to children and adolescents, for whom adherence to ART may be challenging.

Depending on the treatment regimens, the best virologic response was observed with 2 NRTIs + 1 INIs (85.1%) and 2 NRTIs + 1 NNRTI (84.2%), and the multivariate analysis of factors associated with viral suppression showed no significant difference between these treatment regimens. However, compared to the 2 NRTIs + 1 NNRTI regimen, patients on 2 NRTIs + 1 PI had a lower probability of viral suppression. This result could be explained by the fact that PIs can cause gastrointestinal (diarrhea, abdominal discomfort) and metabolic side effects in patients on ART [31], and thus may lead to poor viral suppression in cases of poor adherence. Furthermore, PIs are no more effective than efavirenz, a NNRTI widely prescribed in our study, as shown in the study by Riddler et al. [32], in which the number of patients with an undetectable viral load after 96 weeks of treatment is higher with efavirenz than with lopinavir/r when each of these drugs is prescribed with two NRTIs [33].

Following Chad’s adoption of dolutegravir-based ART—specifically the TLD regimen—as first-line therapy, we set out to compare virologic responses among people living with HIV (PLHIV) between the new ARV regimen and the older ones. Our study showed that 83.3% achieved viral suppression; only 27.8% were treated with the TLD regimen; the viral suppression rate between TDF + 3TC + DTG and TDF + FTC + EFV was identical (85.1%) but higher than that of other ARV regimens. Regarding factors associated with viral suppression, no significant difference was observed between the 2 NRTIs + 1 INIs and 2 NRTIs + 1 INI regimens (p = 0.674), unlike the 2 NRTIs + 1 NNRTI and 2 NRTIs + 1 IP regimens (p = 0.006). DTG is a good alternative to other first-line antiretroviral therapy (ART) drugs, and it is necessary to assess virologic response in patients receiving a regimen that includes this drug.

Our study has certain limitations:

The cross-sectional nature of our study does not allow us to establish a cause-and-effect relationship, but rather statistical associations. Participants were included based on their presence in the collection areas during the study period, and incomplete data were excluded; consequently, our conclusions cannot be generalized to the entire PLVIH population.Data collection took place over a defined period and therefore does not allow for observation of changes in patients’ conditions over time. Initial data collection on viral load, measurement of treatment adherence, measurement of CD4 T-cell counts, and determination of ARV resistance profiles were not performed during this study and will be the subject of further investigations for the follow-up of PLHIV on ART at a later date.

We would like to thank the entire coordination team of the Sectoral Program for the Control of AIDS, Viral Hepatitis, and Sexually Transmitted Infections (PSLSH_IST) for authorizing the use of these data. We also extend our gratitude to people living with HIV (PLHIV) for their open cooperation.