This study which expanded on our previous study in 2015 to broaden the range of HIV-care providers to include regional and low-caseload sites, has again identified very high levels of retention in care PLHIV in Victoria, Australia. Some estimates of retention were in fact marginally higher than the estimates in 2015 [6]. We postulated that smaller and more remote sites may have lower levels of retention in HIV-care, but this was not the case. In addition, some measures of retention were in fact marginally higher than in 2015 [6]. It is also notable that the number of individuals that were considered to have disengaged from care (with unknown outcomes or had unconfirmed transfers) were consistently lower in this analysis. For example, the larger care sites in this analysis had a proportion of individuals with unknown outcomes before the intervention ranging from 0.7 to 2% as compared to 1.1–4.7% of those with unknown outcomes in 2015. The increased proportion with unknown outcomes seen in 2015 demonstrates that the intervention to cross-reference data between sites and contact trace individuals with unknown outcomes is more likely to lead to more accurate estimates of retention in HIV-care rates. In this study estimates of retention in HIV-care including confirmed transfers of care ranged from 80.9 − 98.3% which increased to 83.3- 100% following the cross-referencing data between healthcare sites intervention and contact tracing individuals with unknown outcomes. This was a numerical improvement when compared with estimates of retention in the original study, which were 85.9 − 95.8% pre-intervention and 91.4 − 98.8% post-intervention [6]. Our results align with those of high-income countries with similar quality-of-life indices and publicly-funded healthcare systems to Australia where HIV epidemics affect men, in particular MSM [7,8,9]. Interestingly, we found that study participants who identified as MSM were more likely to have outcomes that remained unknown post-intervention, when compared to other transmission risk categories. Other studies in the United States and Indonesia have found better or comparable rates of retention in care amongst MSM compared to other risk groups [10, 11], Data presented in this study suggests more detailed research beyond just a transmission risk category is important for determining what factors predict unknown treatment outcomes in PLHIV.

There are multiple possible explanations for maintaining or even improving such high levels of retention in care and reducing the number of people with unknown outcomes or unconfirmed transfers compared to the previous analysis. In the intervening period between the two studies there has been increasing importance placed on maintaining high levels of care engagement and the cascade of HIV care in Australia and globally [4, 5, 10, 11]. Our study highlights the need to identify PLHIV with unknown outcomes, and attempt to re-engage them in care to improve individual and population level outcomes for PLHIV. Our research may lead to HIV-healthcare centres initiating or expanding processes to track individuals missing scheduled appointments and perform their own contact tracing interventions to minimise the number of individuals with unknown outcomes. In addition, Australia maintains a publicly-funded healthcare model for PLHIV to access treatment, and there are mechanisms to obtain compassionate access to ART for those PLHIV who are ineligible for Medicare [12].

Our prior study classified individuals as retained in care if they underwent VL testing in a 9-month period, as it was agreed between the participating sites that 6 months was the longest accepted period between clinical review and VL monitoring for patients engaged in HIV-care [13]. Our follow-up study considered individuals to be retained in care if they had a single VL tested in each of 2016 and 2017. This methodological difference in definition between studies may contribute, at least in part, to the observed improvement in post-intervention retention rates in the current study. Notably, this change in definition of care retention could be considered a methodological advantage as it allows for monitoring over more time in the second follow-up period (i.e. 2017), thus increasing the chance of capturing VL testing data in this 12-month period compared with the prior study’s 9-month period. The main advantage of the current study however was the inclusion of more service providers, with different resources and frameworks for patient care [6]. The similar or even improved levels of retention seen in this current study is reassuring given the participation of smaller centres with diverse models of patient care. Another advantage of this study’s methodology to estimate retention is the use of individual-level data when compared to traditional measures relying on ecological data from observational cohort studies, such as national patterns of CD4 count testing in PLHIV [14, 15].

A limitation to our study is that not all HIV-care sites in Victoria were included in the study. Further, we did not investigate for a range of factors that could potentially predict disengagement from HIV-care. Although the proportion of PLHIV with potentially unknown outcomes who were later determined to be retained in care elsewhere in the network is high, the remaining PLHIV not able to be identified as retained in care could be receiving care elsewhere (interstate in Australia, or overseas). The number of such patients who are actually retained in care in this way in unknown, hence the measures of retention in care in this study might be an underestimate.

Risk factors such as psychiatric illness, NESB and ineligibility for Medicare were investigated again due to their significant findings in the prior study to predict disengagement from care [6] but these findings were not replicated. Previous studies have described that approximately 30% of PLHIV in Australia are not accessing treatment or appropriate care, which has been attributed to the complex interplay of emotional barriers such as stigma and fear, practical issues such as lack of knowledge and medical or service-specific barriers, among other reasons [16, 17]. Further studies are needed to investigate these factors to identify potential opportunities for interventions that may encourage retention or re-engagement in healthcare, or to prevent disengagement from HIV-care in the first place.

In conclusion, this study expanded on the work published in 2015 to include a greater cross-section of HIV-care providers and found similarly high retention rates and even lower numbers of people with unknown outcomes of PLHIV in Victoria compared to the first study. This data is reassuring as it demonstrates that retention in HIV-care in Victoria is high and at a level to meet the targets of the most recent Victorian HIV strategy aiming for 95% of people to be accessing treatment [5]. In addition, this work emphasizes the importance of our intervention to capture those who have transferred their care, in addition to implementing systems to trace individuals disengaged from care and attempt re-engagement in care to maximise the number of people in care with access to treatment. The intervention in our study also highlights the importance of keeping updated and accurate patient contact details to prevent loss to follow-up. Ongoing assessments of retention-in-care and determining outcomes for people disengaged from care, or that have transferred care will be critical to map a path to HIV elimination that maximises the number of people in care and able to receive effective ART for individual and public health benefits.